r 0' > "oo^ vOO, V *■ <*,S ■** y ^ * -^ W .9* s s * * '* ; c- "^^ o o vS .-s 8 W X ^. <">, >- V V* V . cV ^> V Or- ** v C* V **% A x >V \ U ^. -A ■0 >0 • -P ^. r>\" ^%^ ."°;. ^0 o. ,-N° s ,0o. A*' -' U v, « V v.. -\\ •>- v ^ < .A v v " ,-0' \ ° V ,0o ^ '• , V * v> % ** V- ^ v4>\^" .0* « <■ -J 1 v5*2. Digitized by the Internet Archive in 2011 with funding from The Library of Congress http://www.archive.org/details/hydrologyfundameOOmead High Falls on the Peshtigo River, Wisconsin, before Development. ( E. C. Wild. ) The Hydro-Electric Development at High Falls. Building Located at Foot of I- ormer Fall. Power Transmitted to Green Bay, Wisconsin, a Distance of about Sixty-two Miles. HYDROLOGY THE FUNDAMENTAL BASIS OF HYDRAULIC ENGINEERING BY DANIEL W. MEAD Member American Society of Civil Engineers Consulting Engineer Professor Hydraulic and Sanitary Engineering University of Wisconsin McGRAW-HILL BOOK COMPANY, Inc. 239 West 39TH Street. New York LONDON: HILL PUBLISHING CO., Ltd. 6 & 8 BOUYERIE ST., E. C. 1919 Copyrighted 1917-1919 BY DANIEL W. MEAD OCi 2u 1919 Blied Printing company. Madison. A535 308 PREFACE In the following" pages the author has discussed some of the most important facts and principles of hydrology. The author believes, from his observations during more than 35 years of professional prac- tice, that more failures have resulted in various hydraulic engineering projects from lack of adequate conceptions, on the part of the design- ing engineers, of the fundamental principles of hydrology and of the importance of hydrological factors than from defects in structural design. In many cases the engineer has based his work on unwarranted assumptions and has not possessed sufficient knowledge even to ap- preciate the necessity of hydrological investigations. As a result of the lack of appreciation of the importance of the fundamental basis on which every sound hydraulic project must rest, numerous irrigation projects, water power plants and public water works have proved partial or complete failures for lack of adequate water supplies, life and property have been destroyed by failures of dams, inadequate reservoir spillways and protecting works, and drain- age and flood protection enterprises have been undertaken with no adequate knowledge of necessary flood capacities. In many ways un- necessary losses are frequently entailed which have been largely due to the fact that the importance of hydrological information has not been sufficiently impressed upon the minds of hydraulic engineers. The author has made no attempt in the following pages to furnish categorical answers to complex hydrological questions but has en- deavored to show that the answers to the same questions may be and sometimes are reversed under different local conditions, and are always greatly modified thereby. He has found it necessary in almost every chapter to warn the engineer against attempts to solve hydrological problems by formulas or rules of thumb of restricted application and to insist in every case upon the necessity of conclusions based upon the detailed consideration of all the local factors in each problem. While the author has emphasized the impossibility of a high degree of accuracy in the solution of most hydrological problems, he has also attempted to show that such problems are susceptible of a solution fully as accurate as in the case of most other engineering problems. While hydrology is by no means a new subject it has received far less study and attention than its importance warrants. Some of the phenomena have been discussed in treatises on water supply and sewerage, but the subject has been introduced as a separate technical study in engineering schools only within the last fifteen vears. vi Preface. In 1904 the author issued his "Notes on Hydrology" as a basis for a course of study at the University of Wisconsin but it was found to be not wholly satisfactory and has long since been out of print. The present work is the result of notes derived from both investigation and practice and has been prepared primarily for the author's classes in the University of Wisconsin. Nothing is introduced which the author has not found to be of practical importance in his own professional work, and much has been omitted on account of the necessary limita- tions of this volume. The literature on the subject is very extensive, and a carefully selected list of the most important sources of informa- tion has been added to each chapter. It is perhaps needless to call attention to the necessity of much further investigation and study in order to correlate correctly many of the intricate factors of hyclrological problems and to make their true relations manifest. On the subject of stream flow, one of the most intricate of these problems, the various methods of correlation which have been suggested by various hydrologists are shown in order to explain both their strength and weakness, and in order to indicate the desirable direction of further investigations. The methods used and suggested by the author for the solution of stream flow problems are not offered as final methods but simply as the best practical methods which in his judgment have been devised up to the present time. The author has endeavored to give credit to the source of all illus- trations and methods in connection with their presentation. He ac- knowledges his indebtedness to the technical press and to various reports, technical works and society proceedings to which reference has been made. His acknowledgments are especially due to Mr. L. R. Balch for material assistance in the preparation of this volume, particularly in connection with the editorial work. Acknowledgments for valuable suggestions are also due to the author's associates, Messrs. C. V. Seastone and F. W. Scheidenhelm. DANIEL W. MEAD Madison, Wisconsin, September, 1919. CONTENTS CHAPTER I Introduction Hydrology — Prevalence of Law in all Natural Phenomena — Hydrological Influence on Early Settlement — Effect of Development on Imporatnce of the Subject — Basis of Present Engineering Practice — Extent of Knowlelge necessary for Successful Engineering Work — Casualties Due to Lack of Hydrological Knowledge — Variations in Hydrological Phenoment — Factors of Safety in Engineering Work — Fundamental Laws — Complexity of Influences — Sources and Limitations of Hy- drological Knowledge — Determination of Hydrological Relations — Danger of General Conclusions — Purpose of the Study of Hydrology — Study of Hydrological Literature — References to Failures in Hy- draulic Engineering Works — Literature 1 CHAPTER II Water — Its Occurrence, Utilization axd Control Importance of Hydrological Conditions — The Occurrence of Water — Cir- culation — The Cleansing and Transporting Work of Water — Precipi- tation — Surface Waters — Ground Waters — Water Supplies — Control of Water — Necessity for the Study of Hydrology — Literature 23 CHAPTER III Some Fundamental Theories Growth and Development — Past Conditions and Their Evolution — Funda- mental Considerations — The Atmosphere — Atmospheric Tempera- tures — .Atmospheric Pressures — The Planetary Circulation — Litera- ture 43 CHAPTER IV Winds and Storms Permanent Winds — Peoriodic Winds — Non-Periodic or Irregular Winds — Cyclones and Anticyclones — The Translation of Storm Centers — Storm Movements — Local Wind Movements — Tornadoes — Hurricanes and Typhoons — Hurricane Movements — Cold Waves — Hot Waves — Hydrological Effects of the Winds — Weather Forecasting — Literature 59 CHAPTER V Hydrography Ocean Currents — Lake Currents — Vertical Lake Currents — Tides — Wind Tides — Seiches — Waves — Wave Motion — Height of Oscillating Waves — Length and Velocity of Oscillating Waves — Energy and Pressure of Waves — Effects of Waves — Literature 89 viii Contents. CHAPTER VI Atmospheric Moisture and Evaporation Atmospheric Moisture — Tension and Weight — Atmospheric Temperatures and Moisture at High Altitudes — Geographical Distribution of Nor- mal Atmospheric Moisture — Variation in Absolute and Relative Humidity — Interchange of Moisture Between Air and Land or Water Surface — Heat Changes Involved in Evaporation and Condensation — Evaporation — Factors of Evaporation — Vapor Tension — Tempera- tures — Wind Movements — Effect of Altitude on Factors of Evapora- tion — Evaporation of Snow and Ice — Evaporation from Land — Effects of Vegetation — General Principles — Measurements of Atmospheric Moisture and Evaporation — Importance of a Knowledge of Evapora- tion and Atmospheric Moisture in Engineering Studies — General Conclusions — Literature 112 CHAPTER VII Precipitation Precipitation — The Ultimate Source of- all. Water Supplies — The Practical Consideration of Rainfall — Causes which Produce or Influence Pre- cipitation — Sources of Atmospheric Moisture — Geographical and To- pographical Conditions Affecting Precipitation — Precipitation in Re- lation to Location near Bodies of Water and Tracks of Cyclonic Storms — Occurrence and Distribution of Rain Storms — Effects of Al- titude on Precipitation — Minor Influences — Rainfall Maps — Occur- rence of Precipitation — Rainfall Accompanying West Indian Hurri- cane — Rainfall Accompanying General Cyclonic Storms — Thunder Storms — Annual Expectancy of Storms — Artificial -Production of Rain — Literature 15G CHAPTER VIII Rainfall Measurements and records The Measurement of Precipitation, instruments Used — Exposure of Rain Gages — Location of Rain Gages of the United States Weather Bureau —The Effect of Wind— Records of Rainfall of the United States- Dependability of Precipitation Records — Estimating Rainfall on any Area — Literature 187 CHAPTER IX Annual Rainfall in the United States and its Variation Quantity and Distribution of Average Annual Rainfall — Variation in Annual Precipitation — Variation in Annual Rainfall in Limited Areas — Variation in Local Annual Rainfall — Detail Study of Local Variation in Annual Precipitation — Cycles in Rainfall — Extreme Variations in Local Annual Rainfall — Expectancy of Future Rain- fall Occurrences — Rainfall Data and the Law of Probabilities — Ap- plication of Probability Calculations — Literature 200 Contents. 1X CHAPTER X Seasonal Rainfall in the United States and its Variation Seasonal Variation in Rainfall-Local Variations in Seasonal Distribu tion of Rainfall— Mass Diagram of Rainfall— Seasonal Divisions of the Year for Agricultural .Purposes— Further Analysis of Rainfall for Utilitarian Purposes-Seasonal Rainfall as Affecting Stream Flow 220 CHAPTER XI Great Rainfalls Importance of the Study of Great Rainfalls-Great Rainfalls-Limita- tions of Information-Sources of Information-Frequency of Intense Rainfalls— Local Intensities of Short Duration— Frequency of In- tense Storms of Short Duration— Approximate Maximum Intensities of Short Storms-Studies of Local Intensity— Rainfall for Longer Periods— Intensity over Large Areas— Excessive Rainfall of the East- ern United States— The Application of Data— Frequency of Storms of Various Magnitudes— Time— Area— Depth Curves for Major Storms— The Study of Extreme Conditions of Rainfall— General Conclusions — Literature CHAPTER XII Rainfall and Altitude Importance of Subject-General Considerations— Factors Affecting Amount of Precipitation— Southern California— Southern Arizona- North Eastern Utah— The Relations of Altitude and Rainfall During Single Storms— Rules for Estimating Relations of Altitude to Rain- fall — General Conclusions— Literature 2S " CHAPTER XIII Geological Agencies and Their Work Hvdrological Influence of Topography and Geology— Outline of Causes Productive of Topographical and Geological Changes— Rock Structure and Texture— Erosion— Weathering— Corrasion— Erosion by Wave Action— Glacial Erosion— Movements of the Earth's Crust— Results of Erosion— Origin and Development of Drainage Valleys— Origin of Falls and Rapids— The Origin of Lakes— Permanency of Lakes- Changes in the Extent of Lands— Literature 309 CHAPTER XIV Geology Object of the Study of Geology— Rock Masses and Their General Classifi- cation—Historical Geology— Chronological Order of Geological Time— Division of Strata— The Precambrian Rocks— The Upper Mississippi Valley— The Cambrian Period— The Ordovician Period— The Silurian Period— The Devonian period— Carboniferous Period- Sedimentary Deposits of Later Periods— General Characteristics of x Contents. the Strata — Modifications of the Strata— iPre-Glacial Drainage — The Glacial Period — Work of Glaciers — Glacial Recession— Glacial Drainage — Post — Glacial Drainage — Hydrological Conditions — Gen- eral Geology and Physiography — Investigation of Geological. Con- ditions — Literature 352 CHAPTER XV Ground Waters The Importance of Ground Waters — Origin and Occurrence of Ground Water — Movements of Ground Water — Springs — Artesian Condi- tions — The Underflow of Streams — Temperature of Ground Waters — The Qualities of Ground Water — Velocities and Quantities of Ground Water Flow — Wells — Literature 390 CHAPTER XVI Stream Flow or Runoff Source of Runoff — Importance of the Study of Runoff — Occurrence of Runoff— Difficulties of the Problem— The Factors of Runoff— Pre- cipitation — Geographical Relation of Drainage Area — Topography and Geology of Drainage Area and Channel — Meteorological Condi- tions — Surface Conditions — The Character of the Storage on the Drainage Area — Artificial Use and Control of Streams — Conditions Favorable to Maximum Water Supply and Equalized Flow of Streams — Conditions Favorable to Minimum Runoff — Discussion of Extreme Conditions — Literature 432 CHAPTER XVII . Variations in Runoff or Stream Discharge Importance of a Knowledge of the Variation in Stream Flow — Considera- tion of Public Water Supplies — Consideration of Supplies for Power Purposes — Consideration of Supplies for Irrigation — Consideration of Supplies for Other Uses — Physical Variables in Engineering Prob- lems — Measurement of Stream Flow — Difficulties in Stream Measure- ments — Runoff Data and Their Use — Variation in the Discharge of the Same Stream — Seasonal Variations in Streams — Rainfall and Runoff — The Lag of Stream Flow — The Retardation of Flood Waves — Effects of Storage on Runoff — Variation in Annual Rela- tions of Rainfall to Runoff — Approximating Rainfall-Runoff Re- lations — Percentage Estimates and Empirical Expressions — Varia- tions in Periodic Rainfall and Runoff Relations — Rafter's Curves of Periodic Rainfall Runoff Relations — Discordance in Rainfall-Run- off Relations — Literature 473 CHAPTER XVIII Estimating Runoff Rational Methods of Estimating Runoff — Vermuele's Method — Justin's Method — Meyer Method — Basis of all Methods of Stream Flow Analysis — Runoff Problems — Runoff Problems with Large Storage Contents. xi (Flow Known — Runoff Problems with Moderate Storage (Flow Known) — Runoff Problems with Limited Storage (Flow Known) — Comparative Hydrographs with Large Storage (Flow Unknown) — Estimating Available Flow with Moderate Storage from Comparative Hydrographs — Literature 509 CHAPTER XIX Floods and Flood Flows The Importance of Flood Studies — Changing Conditions and Flood Ef- fects — Great Floods and Flood Loses — Floods of the Lower Missis- sippi Valley — Floods of October, 1911, in Wisconsin — Other Flood Problems of the United States — The Cause of Floods — Time of Oc- currence — Relative Time of Occurrence of the Flood Crest in Rivers — The Rise, Duration and Recession of Floods — Flood Fre- quencies — Are Floods Increasing in Intensity and Duration — The Effect of Storage on Flood Heights — The Intensity of the Flood Run- off of Streams — Runoff from City Areas — Flood Runoff from Drain- age Districts — Flood Flows of Small Streams for Determining the Capacities of Railway Culverts — The Derivation or Selection of Formulas for Flood Flows — The Economics of Flood Protection Work — Literature 544 CHAPTER XX The Application of Hydrology Fundamental Considerations — Applied Hydrology — Water Supply — Com- parative Sources of Water Supply — Factors for Water Supply In- vestigations — Irrigation — Irrigation Investigations — Water Power — Water Power Investigation — Internal Navigation — Investigation of Rivers, Canals and Harbors — The Sewerage of Cities — Factors of Sewerage Projects — Drainage — Land Drainage Investigation — Flood Protection — Flood Protection Investigation — Literature 597 HYDROLOGY CHAPTER I INTRODUCTION i. Hydrology. — Hydrology treats of the laws of the occurrence and distribution of water over the earth's surface and within the geological strata, and of its sanitary, agricultural and commercial relations. Hy- drology in its broadest extent treats of the properties, laws and phe- nomena of water, of its physical, chemical and physiological relations, of its distribution and circulation throughout the habitable earth, and of the effect of this circulation on human lives and interests. This cir- culation is one of the important influences on the growth and develop- ment, or the changes and evolution from past through present to future forms and conditions in the earth's history, and has a most important bearing on the geographic extent of human activities. This circulation of water above, on and within the earth's crust, is as important and necessary in geological change and development as is the circulation of blood in the animal body or the circulation of sap to vegetable life. The latter are also dependent on water, of which they are largely com- posed. The phenomena and laws of all sciences are so interwoven that it has been said if a student has a complete knowledge of any *one he will have a complete knowledge of all. In a practical way, this idea is true to the extent that no science can be satisfactorily acquired without trespassing to a degree on many other sciences. So in the study of Hydrology we must, to an extent at least, seek information from Meteorology, Geography, Geology, Physiography, Agriculture, Forestry, and from the field of Plydraulic Engineering of which Hy- drology is the basic study. Hydrology discusses Hydro-Meteorology principally in relation to the occurrence, distribution, variation and disposal of rainfall and the runoff resulting therefrom in drought and in flood. It discusses the modifica- tions of the runoff caused by evaporation, topography, geology, tem- perature, and various other factors, and the variations in runoff as these factors vary in importance with the location or with the season. The great variations in the unit runoff under similar rainfall conditions but 2 Introduction. different physical conditions, and under similar physical conditions but different rainfall conditions, are investigated, and the marked differ- ences which arise in different parts of the country with these differ- ences in conditions are discussed. The effects of storage, of cultiva- tion, of forestation and of other artificial physical modifications of the drainage area on the flow of streams, are also considered. Hydrology discusses Hydrography and Physiography in relation to the distribution and circulation of water over the earth's surface and the physical features that modify and influence such distribution and circu- tion. It discusses Hydro-Geology or the occurrence of water in the strata, and the laws of its occurrence and flow. This must presuppose or include a sufficient study of general Geology to give a comprehensive knowledge of the geological limitations which must be expected in hydrographic conditions and of the modifications due to geological changes. Water as a geological agent is discussed, and through such study a comprehension of the birth, growth, and the development of drainage systems and of rivers is attained. 2. Prevalence of Law in all Natural Phenomena. — The study of Hydrology demonstrates the prevalence of law in the occurrence of all natural phenomena. Rainfall and its accompanying phenomena are proverbially incon- sistent, but Hydrology shows that there are limitations to such in- consistencies and that those limitations are quite as narrow and exact as those that must be considered in other engineering calculations which must be cared for by the "factor of safety" which is simply a "factor of inconsistency" in the qualities or occurrences of conditions with which the engineer always has to deal. The study of the development of rivers demonstrates that the ap- parently lawless and erratic action Of streams follows laws more or less distinct, which must be studied and comprehended before intelligent river conservancy becomes possible. The laws which control the circulation of water, on which its pres- ence or absence depend, and which modify and define its occurrence, attract attention and become of practical importance only as comprehen- sion of them permits of such adaptation to human affairs as will reduce or eliminate the injurious results which may otherwise happen during the occurring cycle, or will modify or effect a controlling influence which will adapt the occurrence to useful ends. 3. Hydrological Influence on Early Settlement.— In primitive settlements, a profound knowledge of the detail of these laws and con- Hydrological Influence. 3 ditions was of small importance. Normal conditions might render a locality unsuited to human use. The land might be too dry or too wet for agriculture and it would not be utilized. It might be subject to overflow from the tides or the river floods and remain unsettled, or if an attempt was made to utilize or to settle, it was abandoned on account of the rare occurrence of overflow, with more or less resulting loss when such overflow occurred. As land was abundant and of but little value, the individual had but to choose the location where the conditions were best suited to his purpose. The first settlements of a new country have normally and perma- nently occurred where water for drinking and other domestic uses was readily obtained ; where the normal rainfall, both in quantity and dis- tribution, was adequate for agriculture ; where the land was free from both drought and overflow ; where intercommunication among settle- ments was readily accomplished; where the location was accessible to navigation ; and where water power could be cheaply and readily de- veloped for primitive manufacturing. All of these elements have had an important influence in the development of every country. The earlier civilization developed along those seas, lakes and rivers where navigation was possible and where other elements were favorable to settlement. As the art of navigation developed so that the ocean could be crossed, the early settlements in new lands were along the shore where good harbors were found and where safe and ready ingress and egress were assured. Exploration and settlements followed the lines of navigation, and in America, the St. Lawrence River, the Great Lakes, and the Mississippi and Ohio Rivers afforded the lines of least resistance to the explorer and the settler. The settlement of New York spread up the Hudson and along the tributary rivers because of accessibility together with other favorable conditions, and the Delaware and James Rivers and Chesapeake Bay had a similar influence on the settlement of Pennsyl- vania, Maryland and Virginia. As other methods of transportation have developed, interior towns remote from navigable waterways have resulted, but the larger com- mercial communities are still situated where navigation as well as other means for transportation is available. 4. Effect of Development on Importance of the Subject. — With the growth and development of the country, other hydrological factors exerted their influence. The water powers of Lowell and Holyoke were the prime cause of early industrial development at these places. 4 Introduction. The same influences prevailed at numerous other locations in the East. The growth and concentration of population soon affect land values, and lands at first unutilized, on account of unfavorable hydrological conditions, gradually attract attention on account of their favorable lo- cation, and the questions of their reclamation, protection and utilization become of increasing consequence. A knowledge of the conditions that influence such lands gradually became important. The limits and ex- tent of the unfavorable conditions were examined and considered ; primitive attempts were made at their reclamation, often with destruc- tive results because the extreme conditions were unknown or unrecog- nized. Mankind gradually determined, by dearly acquired experience, the necessary extent and limits- of its powers. In some cases limiting values required only small effort ; in others the values were so great that extensive efforts and expense were warranted. In early reclamation work only crude efforts were possible for no knowledge or precedent existed, but as the development proceeded, the principles underlying successful work were made manifest, the in- fluences of conditions were determined, and the results of similar efforts were more readily and certainly assured. 5. Basis of Present Engineering Practice. — Modern engineering endeavor is a development from the successful primitive efforts of the pioneer to better his condition, to make his home and prop- erty safe and accessible, and to secure and surround himself with the conveniences of civilization. From the experience of man in all climes and in all countries, have been established the principles on which the success of all engineering work depends. There is little essentially new or novel that is safe. The adoption or extension of past experience to new circumstances and conditions is the sound basis of successful work. Research alon'g new and original lines is but mod- erately productive and is seldom warranted in the solution of practical problems ; that 'is the function of the pioneer and the laboratory. The engineer with the great practical problem must call to his assistance the successful experience of the past, and must build along lines that do not admit the possibility of failure. It becomes therefore of funda- mental importance for the engineer first to recognize his problem, and all of the conditions and principles on which its solution depends, for the correct solution can depend on nothing less. 6. Extent of Knowledge necessary for Successful Engineering Work. — In the application of any science to practical ends, it must be remembered that for real substantial success a knowledge of many Hydrological Influence. 5 sciences and many facts is essential. Hydrologically, a water supply for any purpose may be satisfactory but it must be conserved and de- veloped by correct engineering design and construction to be an engi- neering success. Successful adaptation of sound engineering and con- struction may bring about satisfactory constructive results but still other things are needed for ultimate success. The legal aspect demands attention, the laws of the land must be observed, and the legal rights must be properly secured, but even more is needed. Business and financial conditions must also be considered. Can the proposition be made a commercial success? Will the use to which the project is to be put warrant the necessary financial outlay and produce a sufficient income to guarantee satisfactory results for the investment necessary for sound engineering work, under the laws of the land, and develop the hydrological resources to the extent required? For real success, each aspect is both independent and related to all others ; failure in one is failure in all. No one is the most important unless unrecognized, when its importance at once predominates. At least a limited understanding of hydrological principles is prerequisite to the successful solution of the simplest problems in hydraulic engi- neering. For the purpose of investigating the more complicated prob- lems, a more detailed knowledge of this science is essential, and the more extended the knowledge of this subject, the greater the assurance of the successful solution of all such problems. 7. Casualties Due to Lack of Hydrological Knowledge. — Failures more or less serious have resulted in every branch of hydraulic engi- neering from the neglect to investigate the fundamental hydrological conditions and to appreciate the importance of fundamental hydrologi- ical knowledge. Water power installations have been built without sufficient knowledge of the regime of the stream on which their success depends, resulting in failures of greater or less consequence. In many cases the deficient supply has resulted in financial failure, the plant being perhaps continued in operation after liquidation by the original investors. In some cases even more marked failures have resulted. A water power plant, taking its supply from a mountain lake, was constructed a few years ago in Virginia. The lake was drained by the plant soon after operation began, and the dependable supply was found to be so small that the plant was abandoned. A dam and power plant were constructed within the decade on a Wisconsin river which proved to have a normal flow so deficient in quantity that the dam was abandoned and the 6 Introduction. machinery moved to another location on a larger and more dependable stream. To the lack of proper geological knowledge and investigation must be attributed many expensive and serious failures. The failure of the dam at Austin, Texas, 1 was due to faulty foundation construction in the poor quality, open textured and faulted limestone. Similar con- ditions coupled with poor construction propably gave rise to the dis- astrous failure of the dam at Austin, Pennsylvania, in 191 i, 2 and of the Stoney River Dam in West Virginia. 3 Cities have been founded in needlessly exposed positions and left unprotected, or so poorly protected as to be subject to great financial damage and loss of life from floods. Extensive damages have also been caused to farm and agricultural communities from similar causes. The Passaic flood of 1903 4 resulted from an unusually large rainfall and from rapidly melting snow. From October 8th to nth, 11.74 inches of rain fell in the Passaic River basin. All storage on the basin was filled at the beginning of the storm, and in the resulting flood bridges were washed out, a large number of dams failed, many high- ways were destroyed, and much damage occurred to manufacturing plants and real estate. In the Kansas City flood 5 of the same year, a rainfall of five to ten inches occurred in sixteen days on the drainage area of the Kansas River, at a time when the river was above its normal flow and with the ground saturated. At Lecompton, the gage was twelve inches higher than any readings in twenty-two years. At Kansas City, the flood was fourteen feet above the danger line and two feet above the highest point reached by the previously highest recorded flood of June 20, 1844. The damage that resulted was very great. The Johnstown flood, 6 which occurred in 1889, was probably one of the greatest disasters of the kind on record. This disaster was due to the insufficient provision of spillway. Continued rains saturated the soil and caused practically all of the water of a succeeding heavy storm 1 Water Supply Paper No. 40, by T. U. Taylor. Eng. News, September 5, 1901; Eng. News, April 12, 1900. 2 Dam Failure at Austin, Pa. Eng. News, March 17, 1910. 3 Break in Stoney River Dam. Eng. News, January 22, 1914. 4 Passaic River Flood of 1903. New Jersey. U. S. G. S. Water Supply & Irrigation Paper No. 92, M. O. Leighton. 5 Kansas City Flood of 1903. Destructive Floods of 1903, by E. C. Murphy. U. S. G. S. Water Supply and Irrigation Paper No. 96.' ' 6 Johnstown, Pennsylvania, Flood of 1889. Eng. News, June 1, 8, 15 and 22; July 13, and August 17, 1889. Casualties Due to Lack of Knowledge. 7 to run off rapidly, raising the water in the reservoir and finally over- topping and destroying the earth fill dam, and releasing a great flood of water which descended on the unprotected cities and villages below with great loss of property and life. Over five thousand lives were lost in this flood, and the property damage amounted to many millions. The insufficient provision of capacity for passing flood waters caused the destruction of the reservoir dam at the Dells of the Black River in 191 1. 7 While the spillway of the lower dam at Hatfield was undoubt- edly adequate for normal maximum floods, the sudden discharge of some 14,000 acre feet of water into the lower reservoir, resulted in the water overtopping the earth fill portion of the lower dam. Perhaps 10,000 additional acre feet of storage were released from the lower res- ervoir, and the resulting flood destroyed the principal business district of the city of Black River Falls, Wisconsin, entailing a large loss of property, though fortunately no lives were lost. The great flood in the eastern United States in March, 1913. which caused a loss of perhaps four hundred lives and $100,000,000 in the Miami Valley alone, was due to an excessive rainstorm accompanied by other unfortunate physical conditions and so centered over certain drainage areas as to cause an unusual flood state. 8 These floods demonstrate the lack of fundamental data in regard to the possible extremes of such occurrences, and emphasize the necessity for more extensive investigation and observation of both rainfall and stream flow, and the effect of other physical conditions on these occur- rences. The loss of more than six thousand lives and over $17,000,000 in property in the city of Galveston, on September 8, 1900, 9 due to a West 1 Black River, Wisconsin, Flood of 1911. Eng. Record, October 14, 1911. s Wabash River Flood, March 21— April 2, 1913, by R. L. Sackett. Eng. News, April 24, 1913. Recent Flood at Columbus, Ohio, by Julian Griggs. Eng. News, April 10, 1913; see also Eng. Rec. April 19, 1913. Flood Devastation at Dayton, Ohio. Eng. Rec. April 12, 1913. Flood of March-April, 1913, on the Ohio River and its Tributaries, by John C. Hoyt. Eng. News, April 10, 1913. The Ohio Valley Flood of March-April, 1913, by A. H. Horton and H. J. Jackson. U. S. G. S. Water Supply Paper No. 334. 9 Galveston, Texas, Flood of 1900. The Encyclopedia Americana. Sci- entific American Compiling Department. The Lesson of Galveston, by W. J. McGee. National Geographic Maga- zine, Oct. 1900. 8 Introduction. Indian hurricane which drove the water of the Gulf of Mexico over the city, was a serious lesson on the protection of cities from unusual conditions which are not, and perhaps cannot always be foreseen or ap- preciated. The occurrence of a similar storm in 1915, 10 and the result- ing casualties show that Galveston and other cities along the Gulf of Mexico are frequently subject to such contingencies and have not as yet taken the precautions necessary for their safety. In the last few years, failures in various irrigation projects, due often to inadequate water supplies, have been numerous. In few cases are the facts available, for those who have suffered from such mis- takes have usually preferred to bear these losses quietly and not make public the cause of such failures. Only in the case of the work of the United States Reclamation Service are facts of this kind available. The Hondo Project 11 of the United States Reclamation Service in New Mexico, was designed to take, its water supply from the Hondo River. The river has an intermittent flow only, but based upon a study of rainfall records, together with a consideration of the possible runoff due to topographical conditions, the construction was under- taken with the expectation of operating on stored flood waters. The construction was completed in 1906, but since that time the runoff has not been sufficient to allow the storage of enough water for practical use. In very many cases in the past, public water supply systems have been designed and constructed to utilize supplies of water which have later been found much too limited for the purpose for which they were in- tended, and expensive changes in the works have thus been made nec- essary ; or such works have been constructed in locations where the supplies have afterwards been found to be polluted and undesirable, with similar expensive results. Iri a certain city in Illinois, a pumping station was located near a spring which was developed by means of a large masonry well. When pumping began, the well was soon emp- tied and the inflow was so insufficient that the well and station were abandoned and a new station was constructed in an entirely different locality. In another case, in a city of considerable size, a well was con- 10 Galveston's Sea Wall Checks Hurricane Devastation, by E. B. Van de Greyn. Eng. Rec. Aug. 28, 1915; see also Eng. News, Aug. 26, 1915, and Sept. 2, 1915. Effect of Galveston Storm on Sea-Wall and Causeway, by R. P. Babbitt. Eng. News Aug. 26, 1915. 11 Hondo Project. House of Representatives. Document 1262 (1911). 3d Session 61st Congress. Variations in Phenomena. 9 structed at a large expense into a gravel deposit which furnished a supply adequate in quantity but entirely unsatisfactory in quality. A limited investigation afterwards proved that the gravel stratum under- laid the thickly settled portion of the city and drained the vaults and cesspools of the unsewered area. Such examples were very numerous in the early days of the installation of water supplies, when limited knowledge and experience had not demonstrated the need of study and investigation. They are much too common even now when the experience of the past is available as a warning of the necessity of a full knowledge of these fundamental conditions. Great losses have been sustained, property ruined, and unsanitary conditions created by the overflow of storm water from sewers and drains of improper design. The records of almost every city will give examples of such occurrences. Unfortunately for the greatest success of future projects, mankind prefers to publish its successes and to conceal its failures, while fre- quently much more might be learned from the latter than from the former. Many of the unfortunate occurrences briefly described above have been due to the lack of investigation and of a thorough understanding and appreciation of the fundamental principles and knowledge of phe- nomena which it is the province of Hydrology to discuss. 8. Variations in Hydrological Phenomena. — Many of the funda- mental phenomena which must be considered in the problems of Hy- drology are exceedingly variable in occurrence as regards quantity, in- tensity and time, much more so, in fact, than the ordinary observer would suspect. It is a common idea that, taking the season through, the average rainfall is not greatly different from year to year either in amount or distribution, yet the rainfall at Madison, Wisconsin, has varied from a minimum of 1349 inches in the year 1895 to a maximum of 52.93 inches in 1881, and the variation in monthly distribution is still more irregular. A better knowledge of these variations is, how- ever, now becoming common through the valuable work of the United States Weather Bureau. The casual observer is not apt to realize the great variations that occur in the flow of streams, concerning which he has no means of exact information. His conclusions in regard to stream flow are usually drawn from personal observation, and his observations on sub- jects in which he has little personal interest are inexact and hence tend to error. Extended and exact observations will show that stream flow 1 Introduction. is subject to extreme variations both in drought and in flood, and the limits of these variations are even greater than those of the rainfall on which stream flow so largely depends. Floods similar to those of March, 1913, in Ohio and Indiana which surpass all previous records, give indications of the possibilities of ex- treme conditions which may occur beyond any which seem probable from the recorded data available. The maximum flood must result from the simultaneous occurrence of all conditions favorable to runoff, and it cannot be said, with the lim- ited records of such phenomena, that such simultaneous occurrence of favorable conditions has as yet been realized even in the most extreme recorded case. The uncertainty of many meteorological phenomena is proverbial. The great variation in the character of the seasons throughout a period of years is very marked. The irregularity in the occurrence of rain and snow, of storms and sunshine, is a matter of common observation. The observer is therefore naturally led to expect that other phenomena, dependent largely or partially on meteorological conditions, will be sub- ject to a similar variation, and be equally uncertain. On the other hand, a few casual observations in which these great variations are seen, might lead to the belief that meteorological phenomena follow no law, or at least follow laws so complicated and involved as to be hopelessly ob- scure. They might also lead the observer to the conclusion that no ascertainable relation exists between rainfall and stream flow, or be- i tween other interdependent hydrological phenomena. Accurate and continuous observations, however, show that while great variations ex- ist, they are limited in character and extent, and that the relations between the various factors of Hydrology and Meteorology, while com- plicated, are nevertheless fixed and by extended observation can be ren- dered sufficiently determinate to enable valuable deductions to be based on them. . It is most important that the engineer should realize both the great variations which occur in these phenomena and the limitations of such variations. The engineer is therefore frequently obliged to draw conclusions of greater or less importance, often from very inadequate data, as to the rainfall, the resulting ground water supply, runoff and their possible extremes from some given source or drainage area. In such cases, he may be obliged to estimate the probable and possible rainfall condi- tions from comparisons with other areas where such data, also fre- quently inadequate, are available, and which areas are similarly located Factors of Safety. 1 t geographically, topographically and meteorologically, and where, on 'account of such similarity of location and conditions, similar inten- sity and magnitude of rainfall may reasonably be anticipated. It is readily demonstrable that local conditions are never exactly du- plicated and that any comparisons, between apparently similar locali- ties are subject to possible errors of considerable magnitude. Hence, estimates of rainfall and runoff, and the design of structures based on such comparisons, must for safety be made with these probable errors in mind and must include factors of safety proportional to the possible errors involved and the serious nature of possible casualties which might result from designs based on such erroneous data. In considering these problems it is important to recognize the fact that general principles frequently are subject to wide variations, and even to marked exceptions, especially when relating to the compli- cated subject of meteorology. It is highly essential therefore in as- suming that any general principle may or will obtain in a given lo- cality to secure sufficient data to demonstrate that all conditions are favorable to the probable prevalence of such principles and the prob- able force or intensity of the phenomena resulting thereunder. It must also be remembered that only limited conclusions should be drawn from limited observations. In many cases, conclusions based on data for single months or years would be entirely reversed if based on observations for other similar periods ; and both would be altered if based upon the average and extremes shown by long series of ob- servations. 9. Factors of Safety in Engineering Work. — In all engineering work the contingencies to which any structures or plant will be sub- jected are of necessity more or less indeterminate, and the lack of exact information as to the actual conditions which will prevail, and which will influence the character and usefulness of a structure or plant during its life, require that, in order to provide for such unfore- seen conditions, a factor of safety shall be used and that the structure or plant shall be designed much stronger, larger or on different lines than the average condition would apparently make necessary. In the projects of hydraulic engineering, similar factors of safety must be ap- plied as in structural design. In hydraulic calculations, and in the cal- culations of the volume of flood and of low water flow, no large factors of safety are financially possible, and the supply or capacity of plants or works must be designed for essentially the results desired with only a small margin for safety. It will therefore be seen that, in carefully 1 2 Introduction. made hydrological calculations, the probable inaccuracies are, in spite of the great variations before noted, no greater than in other engineering works, and, although there is much need for extended ob- servations and research, yet the applied science of Hydraulic Engineer- ing is, in exactness, fully abreast with other branches of engineering. 10. Fundamental Laws. — Natural laws are always dependable and similar effects always result from similar causes. The difficulty of in- terpretation lies in the difficulty of differentiating and recognizing the causes to which the effect is due. Successful engineering work is the result of successful differentiation of the underlying facts and princi- ples, and the success of other work based on successful precedent lies in the ability to discern similarity of conditions, or to modify the de- tail so as to meet the new conditions involved. While the fundamental laws of Hydrology are unchanging, the factors which control their phenomena are so numerous that they result in wide variations in the relations of similar phenomena in different localities. As with all phy- sical phenomena, similar causes, when acting under similar conditions, produce similar results ; but the causes, and the varying conditions un- der which they act, must be carefully investigated and thoroughly un- derstood, in order that the result may be rightly anticipated. With the great variation in the circumstances of occurrence, it is therefore un- safe to apply data obtained from one locality, under one set of condi- tions, without modifications, to an entirely different locality' with rad- ically different conditions, and expect similar results. The laws of nature cannot be modified by human agencies, but such laws may be utilized under favorable conditions to accomplish results favorable to humanity. A knowledge of the conditions and of natural laws becomes of great irnportance when such adaptation becomes desir- able, and the degree of success assured in the desired adaptation corre- sponds with the extent of the knowledge possessed and applied. ii. Complexity of Influences. — Hydrological. problems are fre- quently difficult to solve on account of complexity of the influences involved. The geological, physiographical, topographical and mete- orological conditions vary to considerable extent, with every de- gree of latitude and longitude, and often with even less extended geographical differences. The meteorological conditions vary as greatly, and sometimes even more greatly with the change of sea- sons than with the change of locality. Each locality has therefore a combination of conditions more or less different and distinct from those of every other locality, however near or remote, and the laws Sources of Hydrological Knowledge. 1 3 which control the occurrence of local phenomena are more or less modified by such local conditions. Hence, the local conditions must be investigated and determined before correct conclusions can be drawn concerning the dependable occurrence of hydrological pheno- mena. There are, however, geographical limits within which similar physio- graphical and climatic conditions prevail, and where hydrological con- ditions are so similar that conclusions, based on the data of one locality, can be applied, with only slight modifications, to other localities within such limits. If this were not the case, a science of hydrology would be impossible. The greatest difficulties encountered in the study of this sub- ject are these variations and the determination of their effect on phe- nomena. For accuracy and exact determination, sufficient data are not always available, hence the available data become still more valuable and the extension of these data becomes of great importance. 12. Sources and Limitations of Hydrological Knowledge. — Our knowledge of hydrological phenomena is at the present day fragmentary and incomplete. While knowledge in the natural sciences has made great strides in the last two centuries, and our progress in many lines has been phenomenal, the value of a knowledge of the many hydrological data necessary for the satisfactory practice of hydraulic engineering has been but slowly realized. Rainfall observations have been made in a few isolated cases for perhaps 150 years or more, but anything like a systematic study of rainfall, even in the old countries of Europe, is of comparatively recent date. A few isolated rainfall observations, more or less continuous, were made in America in the iSth century. Several additional sta- tions were established and, although sometimes changed in location, have in this way been continuously maintained since early in the 19th century. By 1850, the number of stations at which such observations were made was considerably increased, and these stations were greatly extended when systematic work of this sort was taken up by the Sig- nal Service about 1870. The most of the precipitation stations have, however, been established since the organization of the Weather Bureau in 1891 ; but while these stations have already increased in number to 4,971, they are even now too limited to afford data for the satisfactory solution of many problems important to the hydraulic engineer. Where rainfall must be used as a basis for estimating the hydrological conditions for long periods in the future, it is evident that such data should be available for long periods in the past, and the com- 1 4 Introduction. paratively recent establishment of present stations, therefore, makes it clear that our knowledge in this regard is much too limited. On the subject of streamflow the data are still more incomplete. The measurement of flowing water is more difficult than the measure- ment of rainfall, and in very few cases have reliable observations of the flow of any stream been continued for half a century. About 1893, the United States Geological Survey began to accumulate data and to make observations on the flow of streams, and the published reports of the Survey are the principal source of information from which such data can be obtained. Owing to financial limitations, the extent of these measurements and observations is far more restricted than those of rainfall, and the stream flow in many locations and many stream- flow conditions remain essentially unknown and are still to be inves- tigated. In this connection the stream gage height observations collected and made public by the Weather Bureau afford valuable data from which, by comparison, more limited observations can sometimes be extended. Geological data from which hydrological conditions of under- ground water sources may be studied, have been accumulated rapidly in the last twenty-five years and are found in the numerous volumes published by the United States Geological Survey and by the geological surveys of the various states. The development of all of these branches of knowledge goes hand in hand with civilization and has been extended as settlement has ex- tended and as the prospective demand of civilization has pushed the frontier of knowledge farther and farther into hitherto unknown re- gions. The work of the hydraulic engineer is frequently required to make settlement possible, hence in many cases hydrological problems arise in regions where such investigations have never been made or have only just begun. The difficulties that arise in such cases must be known and appreciated in order that the work of the engineer may be conducted on conservative lines and result in developments whose ac- complishments will assure the success and permanency of social domin- ion over the new lands. 13. Determination of Hydrological Relations. — In considering the involved question of hydrology it is most important to disabuse the mind of personal bias and to leave it as free as possible to form conser- vative and logical conclusions from the best data available. It is a common experience that man}- men formulate an hypothesis Determination of Relations. 1 5 and gather data to prove it instead of first collecting the data and form- ulating an hypothesis therefrom. With sufficient bias almost any con- clusion can be reached to the satisfaction of the prejudiced investi- gator. All correct hypotheses must rest upon either or both inductive and deductive reasoning, and to the extent that the hypothesis fulfills the requirements of both methods it may be regarded as correct. Inductive reasoning consists in establishing a general law on many observations in which a certain effect is found to follow a certain cause. This process depends fundamentally upon eliminating so far as possible other contributing causes so that the effect in question may correctly .be attributed to the one contributing cause. As the factors become complicated, the results of such investigations become uncertain and can finally be demonstrated in a satisfactory manner, if at all, only by extended investigations and when the main cause is so predominating as to produce an effect in spite of other complicating factors. If, for example, it is desired to investigate the relations of annual evaporation from soil to annual rainfall (see Sec. 74), the results of a long series of observations, under conditions where other factors are as similar as possible, are platted with annual evaporation and annual rainfall as ordinates and abscissas respectively and the relations of these platted points are observed. (See Fig. 85, page 140). If the annual evapora- tion were essentially constant, regardless of the variation in annual rainfall, the observations would fall approximately on a horizontal line representing the mean annual evaporation. If, however, the an- nual evaporation increases with rainfall, as seems to be true, such fact will be indicated by the relative location of the points on the drawing ; and if the centers of gravity of the higher and lower groups of points respectively be determined, the location of such centers of gravity will indicate the direction of an inclined line which will more clearly rep- resent the mean annual relations of evaporation and rainfall. It will "be noted from Fig. 85 that for the two years in which rainfall was 23.5 inches, the evaporation was 13.9 and 22.2 inches respectively. This would seem to indicate that the general hypothesis is incorrect. The departures of the various observations from the line of mean an- nual relations so established do not, however, indicate that the hypo- thesis is incorrect but they show that other factors are present which frequently so influence and obscure the relations of the two factors ■considered that they may frequently overcome the general relations established. The relations of various factors in different phenomena may be in- 1 6 Introduction. vestigated in a similar manner and experimental curves 12 established showing the relations found which may be reduced to formulas more or less broadly applicable. The ultimate truth of any hypothesis ad- vanced or of any formula proposed is confirmed when it is always found to apply to extended series of observations in the investigation of which it can be consistently employed. Relations so determined are both quantitative and qualitative and are therefore of the greatest use to the engineer as a basis for his conclusions. Deductive reasoning is based on well established fundamental prin- ciples that are known to obtain from previous experiences. From these fundamental principles a certain effect is clearly deduced as a consequence of a certain cause. From such deduction, coupled per- haps with other fundamental principles, other results are found neces- sarily to obtain and the same process is extended until the ultimate conclusions are reached. Here too the process of reasoning is com- plicated by involved conditions which frequently lead to serious error unless every step is closely scrutinized. Deductive logic is the basis of all sciences and its methods are rigidly exact if correctly used. In hydrological problems the results of deductive reasoning are usually qualitative rather than quantitative. In complicated problems of hydrology, the investigator needs the aid of all possible logical methods, and even where every method of logic is applied it is frequently found that on account of limited or in- correct data and lack of knowledge of certain fundamental principles involved, the relations sought can by no means be definitely established. Indications may lead to certain general conclusions, and while such conclusions may be inexact they may be the best possible from the ex- perience and knowledge at hand. Under such conditions any con- clusions must be regarded as tentative only, utilized with caution, and final conclusions must be withheld pending broader observation and more extended experience. i- See Empirical Formulas, by Prof. T. R. Runney. John Wiley & Sons, Inc. 1917. Practical Mathematics, by Prof. F. M. Saxeby. Longman-Green Co., 1905, Chap. VIII. Methods for Determining the Equation of Experimental Curves, by H. S. Landsdorf. Jour. Asso. Eng. Soc. Vol. 32, p. 325, 1904. Determination of Experimental Equations, by L. F. Harza. Wisconsin- Engineer, Dec, 190S. Danger of General Conclusions. 1 7 14. Danger of General Conclusions. — In considering many of the simpler phenomena, the relations between cause and effect are so direct as to be readily understood and appreciated. The very simplicity of such relation is apt to be misleading when more complex phenomena are under investigation and, in consequence, undue weight is often given to some single influence that may be only one of many which modify or control the results under consideration. By complex phenomena are meant those in which the effect is modi- fied by numerous causes, each influencing the ultimate result not only in accordance with its own character and intensity, but also in accordance with the relative character and intensity of other co-ordinate influences. The effect in such cases may be regarded as the resultant of numerous factors, and the weight, importance and effect of each must be care- fully differentiated in order that its relative importance may be rightly understood and clearly appreciated. Most meteorological and climatic problems are of this class ; and many such problems are so involved in character, the factors that modify their occurrence are so complicated and so irregular, and they are often so modified by unappreciated, and perhaps by unknown causes, as to make their occurrence appear to the limited vision of the casual observer as devoid of law and beyond the possible knowledge of mankind. The first common error in the consideration of such problems is the assumption of a simplicity of the relations between cause and effect that is not warranted by fact. The second common error is the as- sumption that when a certain cause is operative under one set of condi- tions that it is operative to a similar degree under all other conditions. The third common error is due to the confusion of cause and effect, or in attributing the cause to the effect instead of the true relation of the effect to the real cause. The rapid advance in fundamental science and the development of many startling and hitherto almost unknown phenomena, applicable perhaps to new commercial development have, in cases, given the un- wary a basis for a belief in possibilities not yet developed, and in many cases, most improbable. This readiness of the public to anticipate great advancement in scientific achievements has been utilized by psuedo scientists to advance immature ideas as though they were established principles and to make unsubstantiated claims for personal or class reasons. In many cases such claims are advanced in good faith, based on only a partial examination of all the data of the problem. There are those who, even in the face of the vast number of almost Hydrology — 2 1 8 Introduction. unstudied influences that control the weather conditions and the al- most insignificant data yet available, still believe in the present possi- bilities of long advanced weather predictions. The foresters and their friends see in the planting of trees, which is only one of manifold active influences, the solution of flood troubles and low water conditions. Others, reasoning from cause to effect, assert material increase in precipitation to be due to forests or irrigation ; and in manifold other lines, marked influences on extended phenomena are declared due to limited developments in one of many controlling factors. The engineer must not be misled by psuedo-scientific argu- ment. His analysis must be complete, his conclusions conservative and limited to the case at hand to which his data apply ; and even in ex- tending his personal experience from one field to another, he must keep in mind the new factors which may always be present and which must modify the conclusions which, under other conditions, he has known to be definitely established. Experience is a most important teacher, and much of the knowledge of greatest value in practical life is acquired only by this means. Where certain local conditions in various parts of the world or even in the same country differ greatly, conclusions based on the conditions of one locality must be applied to any other locality only with great care. For example the ice conditions of the Arctic and Antarctic regions give rise to climate and physical conditions which are not fairly comparable with temperate regions where ice is a seasonal phenomenon. Rainfall in one country, or even in a part of the same country, may be well dis- tributed for agricultural purposes, while in another location even a greater annual rainfall may be so distributed as to occasion a serious shortage of moisture during the seasons of plant growth. Again, geological and topographical conditions may make certain phenomena largely local both in quality and intensity, and produce results from such causes which will be greatly different or absent altogether under radi- cally different conditions. The relation of the rainfall to the amount and distribution of water flowing from any given drainage area is a complicated problem. The flow from an area is so directly dependent on the rainfall thereon that it seems some simple and constant relation should be ascertainable between the quantities of each. A brief investigation, however, shows that the modifying conditions are manifold and that the relative im- portance of each influence varies even more widely than the apparent range in the conditions. These influences are so numerous, and their Study of Hydrology. 1 9 modifying effect on one another is so direct and important, that no general and constant relation exists between any one influence and the ultimate results. These facts have led to many misinterpretations and erroneous conclusions in the attempt to establish simple relations which from the nature of the case cannot exist. Many serious errors and resultant losses have been occasioned by the adoption of general con- clusions, based perhaps on an accurate analysis of one series of local conditions, but applied under other conditions where such conclusions- were not at all applicable. Conclusions from hydrological data must therefore be adopted with caution and should generally be confined to limited localities until experience warrants their extension to wider fields. 15. Purpose of the Study of Hydrology. — The purpose of the study of Hydrology is primarily to acquire a knowledge of the extent and limits of the variations in hydrological phenomena, to ascertain the effects on such phenomena of the various physical conditions that ob- tain in any locality, and to investigate the geographical limitations within which the observed phenomena may be applied with greater or less modifications, also to establish as far as may be, such laws as will aid in the determination of the effects to be expected from other physical conditions which are found to obtain. For these purposes the study of Hydrology must include : First: The study of the general physiographical, geological and topo- graphical features of the earth, the factors that have produced and are now modifying such features, and their general hydrological relations. Second: The study in a more specific way of these physical condi- tions and factors in relation to the area of the country to which the practice of the engineer will be largely confined. Third: The study in still greater detail of the hydrology of certain localities where certain important laws or relations are found to be best exemplified. It is the further purpose of this text to emphasize more particularly those lines of hydrological study that are most important, and the nec- essary and desirable direction in which hydrological investigation and study should be extended. 16. Study of Hydrological Literature. — Only a brief examination of the subject of Hydrology is necessary in order to appreciate the complexity of the subject and the extent of the field which must be ex- amined in order to secure the data to demonstrate the principles on which its application must rest. It at once becomes apparent that a 20 Introduction. single treatise can do little more than point out the main underlying principles, and illustrate the same with a few general data which will indicate the direction and extent of the variation which must be antici- pated and the character of the further investigations needed in the solution of local problems. In the actual application of these princi- ples to practical work it is evident that they must be studied in the light of a detailed knowledge of local circumstances and conditions,, and that in every case those principles which are to be directly applied must be considered in much greater detail than can possibly be done in any single volume. It is not the hope of the author to offer a complete treatise on this subject to the student or engineer, but only to point out the general relations that have been established, the general principles that are involved, and the necessity that exists for further research and study before any concrete problems can be solved even approxi- mately. There is now in existence an extensive literature on various hy- drological subjects, otherwise this book could not be written. While confining these pages to a brief consideration of the fundamental prin- ciples on which Hydrology rests it has also been the purpose of the author to point out, so far as possible, the source of the data which have been utilized and the further sources of information which are available for a more complete study of the various phases of the sub- ject. In the solution of any concrete problem, the various publications which are noted in the list of literature following each chapter must be consulted in detail, and conclusions offered by the author should be accepted only so far as the data on which they are based seem to war- rant. As noted in Section 14, general conclusions must be accepted with care and applied only when fully substantiated by all the local data which are available. Only by the greatest care can the correct conclusions be drawn for any specific hydrological problem, and even conclusions so reached are subject to various uncertainties. The broad- est investigation and study are essential to a sound conception of the various problems which the engineer must meet. 17. References to Failures in Hydraulic Engineering Works. — The student or reader should study one or more of the following failures, and prepare a statement concerning the cause and results of the failure, and the nature of the information which should have been acquired or investigation which should have been made in order to have assured success. Failures. 2 1 1. Johnstown, Pa. The Johnstown Disaster. Eng. News, June 1, 8, 15, 22; July 13; Aug. 17, 1SS9. 2. Austin, Texas. Failure of Masonry Dam. Eng. News, Feb. 22; April 12, 19; May 10; June 21, 1900; Eng. Rec. April 14, 21; May 2G; June 9, 30; Juiy 28, 1900. 3. Fishkill, New York. The Failure of the Melzingah Dams of the Fishkill and Matteawan Water Company. Eng. News, July 22, 1897. 4. St. Anthony Falls, Minn. Effects of Mississippi River Floods on the New St. Anthony Falls Dam at Minneapolis. Eng. News, May 13, 1897 5. Minneapolis, Minn. Failure of a Minneapolis Dam by Ice Pressure. Eng. Rec. May 13, 1899; Eng. News, May 11, 1899. 6. Collingswood, N. J. Standpipe Failure. Eng. Rec. Jan. 20, 1900. 7. Elgin, 111. The Failure of the Standpipe. Eng. News, May 3, 1900. 8. Providence, R. 1. The Failure of Two Earth Dams. Eng. News, March 21, 1901. y. Jeanette, Pa. The Failure of the Oakford Park and Fort Pitt Dams. Eng. News, July 23, 1903; Proc. Engrs. Club of Phila., July, 1904. 10. Cobourg, Ontario. Damage by Ice to a Standpipe. Eng. News, Aug. 18, 1904. 11. Phoenix, Ariz. Construction, Repairs and Subsequent Partial Destruc- tion of the Arizona Canal Dam. Eng. News, April 27, 1905. 12. Hauser Lake, Montana. The Break in the Hauser Lake Dam. Eng. News, Apr. 30, 1908. 13. Fergus Falls, Minn. The Failure of the City Dam. Eng. News, Oct. 14, Nov. 3, 1909. 14. Pittsfield, Mass. The Undermining of a Reinforced Concrete Dam. Eng. News, April 1, 1909. 15. Utah. The Failure of an Irrigation Dam. Eng. Rec. Sept. 18, 1909. 16. New Mexico. The Failure of the Bluewater Dam. Eng. News, Sept. 30, 1909. 17. Necaxa, Mexico. The Slide in the Necaxa Hydraulic Fill Dam. Eng. News, July 15, 1909; Eng. Rec. July 3, 1909. 18. New Mexico. Partial Failure thru Undermining of the Zuni Dam. Eng. News, Dec. 2, 1909. 19. Austin, Pa. Partial Failure of a Concrete Dam. Eng. News, Mar. 17, 1910. 20. Erindale, Ontario. Failure of an Earth Dam with Concrete Core Wall. Eng. News, April 14, 1910. 21. Austin, Pa. The Failure of a Concrete Dam. Eng. News, Oct. 5, 1911; Eng. Rec. Oct. 7, 14, 1911; Proc. Engr's Club of Phila., Jan. 1912. 22. Black River Falls, Wis. Failure of the Dells and Hatfield Dams and the Devastation of Black River Falls. Eng. Rec. Oct. 14, 21, 1911; Eng. News, Oct. 19, 1911. 23. Mineville, N. Y. Failure of the Dalton Concrete Corewall Dam. Eng. News, May 9, 1912. 24. Ohio River. Failure of Dam No. 26. Eng. News, Aug. 22, 1912. 22 Introduction. 25. Ontario, Canada. The Failure of the Dam of the Erindale Power Com- pany. Eng. Rec, April 27, 1912. 26. Winston, N. C. The Failure and Repair of the Winston .Water Works Dam. Eng. News, April 11, 1912. 27. Port Angeles, Wash. Washout of Base of Port Angeles Dam. Eng. Rec. Nov. 30, 1912. 28. Dam and Embankment Failures in 1912. Eng. Rec. Apr. 19, 1913. 29. Stony River, W. Va. Break in the Stony River Dam. Eng. News, Jan. 22, 1914; Eng. Rec, Jan. 24, 1914; Jour. Engr's Soc. of Penn., Apr. 1914. The Reconstruction of the Stony River Dam. F. W. Scheidenhelm. Trans. Am. Soc. C. E., Vol. 81, 1917, p. 907. 30. Tullahoma, Tenn. Failure and Reconstruction of a Small Dam. Eng. & Con., Nov. 11, 1914. 31. California. ' Wreck of the Otay Rock-Fill Dam. Eng. Rec. Feb. 12, 1916. LITERATURE Manual of Hydrology, Nathaniel Beardmore. Waterlow & Sons, London, 1862. Hydrology of New York State, George W. Rafter, Bulletin No. 85, New York State Museum, 1905. Hydrography of the American Isthmus, Arthur P. Davis. United States Sen- ate Document No. 124, 57th Congress, 2d Session, 22d Ann. Rept. U. S. G. S., 1900-01, pt. IV, p. 513. Hydrology of the Panama Canal, Caleb M. Saville. Trans. Am. Soc. C. E., Vol. 76, 1913, p. 871. Hydrography of Nicaragua, A. P. Davis, 20th Ann. Rept. U. C. G. S., 1898-9, pt. IV, p. 569. Elements of Hydrology, A. F. Meyer. John Wiley & Sons, New York, 1917. CHAPTER II WATER— ITS OCCURRENCE, UTILIZATION AND CONTROL 18. Importance of Hydrological Conditions. — The conditions of the occurrence of water have an important influence on the develop- ment of every country. A closer analysis will show that the occur- rence and conditions of waters have even a more important influence than has previously been indicated. Water is and always has been one of the most important, if not the most important, of the agencies of topographical and geological change. To a greater or less degree it dissolves almost every form of mineral matter from the strata, which action is accelerated by the chemical activity of matter held in solution and by increased temperatures. Its expansion as it changes to ice by reason of low temperatures is a power- ful mechanical agency of disintegration. Its erosive effect in its flow from the mountains to the sea, aided by the detritus carried with it, has been a most potent agent in topographical development, and the dep- osition of materials transported to lakes and seas has been a most im- portant agent in geological growth. Without water organic life cannot exist. It is therefore one of the prime necessities of all organic life, and it is the largest constituent of all animal and vegetable matter. Its action as a solvent is here again a most important property in both animal and vegetable physiological processes. About two-thirds of the average human food is liquid. The average adult requires about 4^ pounds of simple liquid each day, with about 2]/ 2 pounds of solid food, which is about half liquid, intimately commingled with solid matter. Nutriment and oxygen are taken up and distributed to the various tissues of the animal body by the agency of the blood, which, is ninety per cent, water, and which also removes the waste products from the system. Vegetation is equally dependent upon water for the solution of food, its distribution to the vegetable tissue, and the removal of waste. Water is not only necessary for the existence of life, but its occur- rence and condition have a marked effect on health. A super-abund- ance may destroy or be seriously detrimental to both plants and ani- mals, and its character as influenced by the matter held in solution or carried in suspension may also have a serious effect on health. Water 24 Water — Its Occurrence, Utilization and Control. draining from settled regions often receives and transports organisms which are prejudicial to the health of man if the water so polluted is Fig. 1. — Forest in the Olympic Foot Hills near Port Angeles, Washington. Annual Rainfall ahout 40 Inches (see page 25). Fig. 2. — Buckhorn Prairie Desert in Central Utah. Sage Brush in Fore- ground. Annual Rainfall about 12 Inches (see page 25). utilized for dietetic purposes. Water on account of its high solvent and transporting qualities, is constantly removing matter from the drainage area on which it falls and transporting it to other regions where it may Importance of Hydrological Conditions. 25 be either beneficial or detrimental. In some irrigated regions the in- troduction of water has made possible successful agriculture, but a too lavish use has frequently brought alkalies to the surface to the detri- ment of plant life, or has turned the desert into a swamp on which agri- cultural products can no longer be grown. For successful agriculture, about 24 inches of annual rainfall, prop- erly distributed through the season, seems to be essential unless an artificial supply of water is provided. About 15 inches of rainfall per year is required for vegetation, and the remainder of the rain- fall is dissipated in other ways. For intensive cultivation, an addi- tional supply can be used to advantage. Where less than 24 inches of rainfall is available irrigation becomes desirable, and with a considerable decrease becomes highly essential (see Figs. 1 and 2, page 24). Water has always afforded an important means for transportation. For foreign commerce and for domestic commerce between points on the coasts and between points on the Great Lakes, navigation offers the most economical method of transportation of bulky materials. In the early development of modern civilization and prior to the evolu- tion of railways, river navigation was highly important. In undevel- oped countries, internal navigation is still the most important means of transportation (see Figs. 3 and 4, page 26). Even with railways well developed^ river navigation may be found more economical than transportation by rail where a permanent market requires the constant movement ot a large amount of bulky freight between river points. Under some conditions, artificial waterways or canals have been found desirable and economical, but they have become less important with the development of railway transportation. Canals for large vessels are feasible only when limited i 1 First: To comparatively short connections between large and important bod- ies of water between which large traffic would naturally exist except for rapids or other natural barriers, as in the case of the Sault Ste. Marie Canal between Lake Superior and Lake Huron. Second: To comparatively short canals which save a very great sailing dis- tance, as in the cases of the Suez and Panama Canals. Third: To short canals connecting the sea with large commercial centers, as in the case of tb,e Manchester, England ship canal. The competition of long lines of canals with rail transportation is however no longer feasible under modern commercial conditions. 1 Preliminary Report of U. S. National Waterway Commission, (Washing- ton, 1910), p. 13. 26 Water — Its Occurrence, Utilization and Control. '\6\7\B\9 101 /;■ i , '3 4. l r, 7 8 9 10 II 12 1 2 3 4 . ' t r 8 9 10 II 12 70° 60° 50° 3 " s ~~-*-— 1. f< %' H ' ■^T^"~- '£& .yj i ""■^ ""^"•^i r*T 5 L-^' ^ | | s >' °a/ ,' ^ — . Fig. 12. — Mean Diurnal Changes in Temperature at Various Stations in the United States (see page 48). The heat changes at the earth's surface are of great importance. Practically all of the heat received at the surface is from the sun. Various rays from the sun received through the earth's atmosphere give rise to various colored light, produce certain chemical effects, and when stopped by opaque objects are converted into heat. ~-'-r /an Feb Mar -:w- ■,% /i -e Qua. :rcr V:. Dec Temp ■'..- Mc Mai/ \june ju!q O.J 7 5 •," ' Mo: :"e. 100° 80° 60° 40° 20° 10° 100° 80° 60* 40° 20° 10° n 0r£ o^-m^ n«® >^\^ 1U f M tig* \y S V * s ~s «i \y — ^ vy Fig. 13. — Mean Annual Variations in Temperature at Various Stations in the United States (see page 48). Atmospheric temperatures are the result of the heat received from solar radiation, both directly by absorption of heat from the solar rays, and also indirectly by contact with and radiation from the surface of the earth. While it is generally believed that the earth's interior still remains at a high temperature, the earth's crust is such a poor con- ductor of heat that this interior heat has very little effect on surface tem- peratures or surface radiation, and the temperature of the earth's sur- 48 Fundamental Theories. face and of the atmosphere is therefore controlled largely by solar radiation. Even in midsummer with the sun at the meridian, its rays reach the earth's surface in polar regions at a considerable inclination, while between the tropics the inclination is comparatively small. The distance of the earth from the sun and the altitude of the sun at the meridian therefore vary least during the year at the equator and most at the poles. In consequence the greatest difference in tem- 70 Dec Jan. Feb. Mar. Apr. May June Ju/y Aug. Sept. Oct. Nov. Dec. Fig. 14. — Variations in Temperature of Air, Water and Earth at Hamburg, Germany (see page 49). perature between day and night occurs at the equator and the least at the poles ; while the greatest annual variation between winter and summer occurs at the poles and the least at the equator. The conditions above described give rise to diurnal (see Fig. 12, page 47) and annual (see Fig. 13, page 47) changes in atmospheric and surface temperatures. Of the incident solar heat, the atmosphere absorbs an average of about 76 per cent, about 50 per cent being absorbed by a cloudless and practically all by clouded atmosphere. 3 Of the solar heat reaching the earth's surface, four times as much is absorbed by the land as by the water surface. The solar rays falling on soils and rocks are absorbed and converted into heat, the effect or warmth depending on the specific heat of the substance and its conductivity which vary greatly with different depos- its. Loose, porous, air filled soils conduct heat slowly, while solid clay soils especially when saturated with water convey heat very rapidly. 3 See Descriptive Meteorology, W. L. Moore, p. 78. Atmospheric Temperatures. 49 The latter are therefore readily heated and quickly cooled and are sub- ject to a great range of temperature. The former warm but slowly and retain their heat which during radiation is replenished from the lower strata ; hence such soils or substances have a small range of tem- perature. The immediate surface areas of the earth undergo the great- est seasonal variations in temperature. As the depth below the surface increases, these variations decrease until a constant temperature prevails which is the balance between the average external and the internal tem- peratures (see Fig. 14, page 48). Water is diathermanous, and the absorption of solar heat takes place only gradually from the surface to considerable depths. Its specific heat is very high, hence it has the capacity to absorb and give off great quantities of heat. This results in reducing the range of temperature variation over a sea as compared with the land. Sea water also de- creases in specific gravity with a rise in temperature which tends to cause the warmer waters always to lie at the surface. In the .case of fresh water, however, the temperature of greatest density is 39. i° Fahr. The snow and ice covering of the higher latitudes obliterates the dif- ference between land and sea. Snow contains a large amount of air and is in consequence a poor conductor of heat ; hence the range of temperature is considerable but is limited in its rise to the melting point. In the temperate zone the snows of winter delay the warming of the soil in spring inasmuch as heat is absorbed by the melting of snow and in its evaporation. The greatest seasonal differences of temperature be- tween sea and land occur in intermediate latitudes where the summer heat is intense. The annual variations in temperatures of the air, of the waters of the River Elbe, and of the earth to a depth of 16.4 feet at Hamburg, Germany, are shown in Fig. 14, page 48.* The surface temperature of the ocean is considerably disturbed and modified by ocean currents but in a general way these temperatures may be stated as follows : SURFACE TEMPERATURES OF OCEAN (MOORE) Geographical Location Annual Change At Equator 82° 84° Fahr. 2° At Latitude 35° N. or S ■. 50° 68° Fahr. 18° At Latitude 70° N. or S 35° 45° Fahr. 10° The net result of the various factors above described is to produce a 4 Ibid, page 91. Hydrology — 4 50 Fundamental Theories. 6C SO' Fig. 15. — January Isotherms (see page 51), 90' GO' W Fig. 16. — January Isobars (see page 51). Atmospheric Pressures. 51 somewhat irregular distribution of temperatures on the earth's surface. This distribution throughout the world for the months of January and July is shown by the isothermal lines on Fig. 15, page 50 and on Fig. 18, page 52, respectively. These lines represent the mean isotherms for the respective months and are modified from year to year by meteorological conditions. They are also modified locally by the passage of storm centers and by anti-cyclonic movements. 33. Atmospheric Pressures. — The heat acquired by land and water surfaces is in turn radiated into or through the atmosphere, thus in turn affecting atmospheric temperatures. Atmospheric temperatures and their variations are the direct cause of atmospheric pressures and '///////////////////////A?//////////////////////////////////////^^^ Heated Area- Fig. 17. — Circulation Due to Heated Area. their variations. The expansion of the atmosphere 6y heat causes an overflow from above the heated area, a local or planetary circulation in accordance with the extent of the heated area (see Fig. ly), and a con- sequent decrease in surface pressure on the heated area. In conse- quence of this law and the relative gain and loss of heat by the ocean and land areas at various seasons, the land areas attain their maximum pressure in winter and their minimum pressure in summer, while these conditions are reversed on ocean areas. (See Fig. 16, page 50 and Fig. 19, page 52, in which the lines represent mean atmospheric pressure for the respective months in terms of inches of mercury. These maps should be compared with the maps showing the isothermal lines for the same period which are shown just above them in Figs. 15 and 18 respectively). For the same reason there is a daily fluctuation in the local barometric pressure, the minimum occurring shortly after the maximum heat of the day. (See Fig. 20, page 53 and Fig. 21, page 54.) These fluctuations 52 Fundamental Theories. 120' iSO f Fig. 18. — July Isotherms. izo' i5d!_ iaoi iso ijtf so' Fig. 19. — July Isobars (see page 51). are often obscured by non-periodic changes caused by the passage of cy- clonic centers or anti-cyclonic centers of disturbance. Normal atmospheric pressure should be symmetrical and practically the same in all places having a common altitude, for the pressure should Atmospheric Pressures. 53 Ch/caao,I//. /SPA Month 1 I t\l t*> * *> Vfc K Fig. 25. — Typical Areas of High and Low Pressures 3 (see page 64). of the earth, similar to the vortex formed in water running out through an orifice in the bottom of a shallow basin. 2 In the northern hemi- sphere, this circular motion is counter-clockwise, but has the reverse direction in the southern hemisphere. The area within the cyclone, where the barometric pressure is less than that in the surrounding area, is called the "area of low pressure." It is the center of the storm and marks the area of ascending air currents. At and near this center there is a calm area of greater or less extent, depending on the •dimensions of the cyclone. In the region of maximum pressure the air does not descend in a vast uniformly flowing mass but in extremely variable, somewhat lo- 2 See Ferrel's Law, Sec. 33, p. 57. s Figs. 25 to 30 inclusive are taken from Bulletin No. 20, U. S. Weather IBureau on "Storms, Storm Tracks and Weather Forecasting." 64 Winds and Storms. calized descending currents, some of them of strong intensities and some weak. The stronger of these movements, which occur around the outer areas of maximum pressure, strike the earth and because of the friction of the earth surface and of the effect of the* earth's rota- tion are deflected to form eddies in the atmosphere of high pressure called anti-cyclones. The atmospheric movements due to the pressure variations are relatively light and the consequent anticyclonic circu- lation is slow. The result is that such systems do not endure for any WM Pig. 26. — General Paths of Atmospheric Pressure Transition 3 (see page 65K considerable period but are constantly being dissipated and recon- structed. After their formation they break away from the main areas of maximum pressure and are carried eastward with the general east- ward drift of the atmosphere and in their translation become an active factor of variable winds. 39. The Translation of Storm Centers. — On every weather map are shown areas of high and low pressure produced by conditions that have already been discussed. The low pressure centers are called the storm or cyclone centers ; the high pressure centers are called anti- cyclone centers, and the winds blow around these centers in the gen- eral direction of the hands of a clock but less distinct than in the cy- clone (see Fig. 25,* page 63). Inside the area covered by the closed isobars of the cyclone, the circulation is upward as well as counter- clockwise, while on the area covered by the closed isobars of the anti- Translation of Storm Centers. 65 cyclone, the atmospheric movement is downward, bringing cold air from high altitudes. Between these centers is an atmospheric pressure gradient of greater or less magnitude, which causes the air to flow from the high areas to the low areas with an intensity depending on the difference in pressure between these two centers of atmospheric action. In addition to the atmospheric movement, there is also a movement of these centers on more or less definite paths across the country from.' west to east. The anticyclones or high centers enter the country dur- Fig. 27. — Divisions of the United States for the Study of Storm Movements ing the winter in general from the northwest. In the summer months the high areas enter the United States from the Pacific and pass south- easterly to Florida or, after entering the country northerly along the Columbia River, they follow easterly to the Gulf of St. Lawrence From October to March, many areas of high pressure enter the States near the one hundred and fifteenth meridian and either follow along the mountain slope to the southern route or turn abruptly eastward over the lakes to the New England States. The general routes de- scribed are shown in Fig. 26, page 64. Storm centers or centers of low area are of more general and local origin. The United States Weather Bureau has adopted nine districts in its study of the local origin of cyclonic storms, and Fig. 27, page 65, shows these districts, the number of storms which were first observed therein and the gen- Hydrology — 5 66 Winds and Storms. eral direction or path of translation of the storms that formed in each district during the ten years' time from 1884 to 1893, inclusive. 40. Storm Movements. 4 — The points at which storms originate and their paths, as previously indicated, vary with the seasons. The origin and paths of storm centers, with the number of storms that originated in each district for each month of the year during the ten-year period from 1884 to 1893, inclusive, are shown by Figs. 28, 29, 30, pages 67, 68 and 69. The actual daily barometric conditions which ob- tained during the passage of certain storm centers for the period of March 20-23, 1913, are shown on the four diagrams of Fig. 31, page 70. These storms originated in the northern Pacific district, passed southeasterly through Colorado, thence northeasterly over the Great Lake region, leaving the country from the extreme northeast. The storm, which was centered over Lake Michigan on March 20, lost its force during the following twenty-four hours and was dissipated. The storm center, which was centered over the southwestern plateau region on the 20th, developed rapidly in intensity and moved northeastward across the Great Plain and was centered on the 21st over the Great Lakes. It was accompanied by strong shifting gales and widespread precipitation, and was followed by a cold wave of unusual severity for March. On March 22, this storm had reached the mouth of the St. Lawrence, but rain was still falling in the Eastern States. On March 23 a third widespread storm had moved forward from Nevada to Colorado and was moving toward the Great Lake region with increas- ing intensity. The above conditions were those which preceded the heavy rains of March 23-27, 19 13, which produced abnormal floods in the Ohio Valley and the northeastern United States, and the further progress of this storm is illustrated- by the four maps shown in Fig. 146. 41. Local Wind Movements. — As shown by Fig. 23, page 60, the United States is in the belt of prevailing southwesterly winds, and the general drift of the atmosphere is toward the northeast, as shown by Figs. 27 to 30 inclusive. The prevailing winds of any locality may however vary greatly from this general direction, and the passage of storm centers will in each case give rise to radical variations in the local wind direction for the reasons described in Section 38. Local winds are greatly modified by local topographic conditions and the relative heating of land and water surfaces; they also increase in 4 See Bulletin No. 20, U. S. Weather Bureau, "Storms, Storm Tracks, and Weather Forecasting." Storm Movements. 67 V, s, -J^ rX ^^7\> 1 D (0 §sg ^J^f^ = ~> r\°l V^ 1^ Ti w ^|>ol f J -c N \^ O-L - A^rtT 1 -A«\ '113- VV/Tg"P_ "h ^W 7/1 MX 1 f 1 jj \ VAn^ / / !v y JO p- /?y /// K 1 &r 1= p^n Aw R^ / >/" H/C i PT ■TJ (7 ^ $ i/~ «m "5 1 «» 68 Winds and Storms. 0) V« c % ,„ ? ° tf V V if^Nr Nh--i t> ** J^ uL kv° 7^o>— % y/^ 1 r l« £ -^\ V-Vw^~4S*p' 1 w \y \ ^>H \ p \ ,3j> tj 7 s V 13 f/j \ -7 ^s^ ^ ? f/v >r * A ~~i£ i /' / :^ ^hxi 15' $) /> / *V ■/ 1 / ^"y 1 Jpr 1 /^ "^tl^ T^ /\^£^^^ r3^p-20f ^ W//> s\\ 1 J&S-. ^ i^ »c ( ^^L^-^^C n" -?^Y^/i?r ¥^i ^-^ ^- — aST^ _^ Ti-3 Fr!?V/0 j ' v v\ ^^662 ror+At / 31 K C SH f^rP^Tt/ "~~y* //5 ^£^_ PMk F§1 fci>S ^7e? eee^ =^Ef3 ^0^^% "~5r- ^=5?^^ - Local Wind Movements. 71 intensity, with the elevation above the ground surface and near the ground surface with the daily advent of the sun's heat (see Fig. 32, page 71). At stations of high elevations and at all high altitudes the change in the velocity of the wind with the advent of day is reversed from that at stations of low elevation, and the velocities of the wind at night exceed those of the day. (See Fig. 33, page 72). The in- crease in the wind's velocity with the height above the earth's surface 0-M. Noon p.m. Z 3 A 5 6 7 8 9 /O // 12 / 2 3 A 5 6.78 9 10 1 1 Fig. 32, -Diurnal Variation of the Wind near the Earth's Surface, Atlantic City, N. J. 5 is less where the station is located near level water or prairie surface and greatest near broken and forested portions of the country. The average hourly velocity of the winds in various parts of the United States, estimated for elevation of ioo feet above the ground, is shown in Fig. -34, page J2, and the diurnal march of the wind veloci- ties near the earth's surface at both low and high altitudes is shown by Figs. 32 and 33. While the direction of the local winds varies from day to day and even from hour to hour, due to the passage of storm centers, certain 5 Figs. 32 to 36 inclusive are taken from the Year Book, Department of Ag- riculture, 1911. See article on The Winds of the United States and their Eco- nomic Uses, by P. C. Day, p. 337. 72 Winds and Storms. a.n Moon P.M. 12 3 4 5 6 T 3 9 10 1/ 12 I 2 3-456 7 8 3 10 // /2 23 / — I — 1 — 1 — 1 — Jonc/ory 27 I - 28 - i 1 — (_ 1 1 4. Q tfH? 5>Q i \ ^< ,r^ *if i^ , f]C tf K 2 ^ r i^ 5 \24 ~(n t -^ \. ? 3 I 1 r «B 1 ^- s i£ ^ /i i ^'n ' ^h.i, \ J r%~ ^P V /5 . i f \ A 'ws 23 '.*tf2^ ^,*~ ^ ** 1 ■^-T 1 \ lit ^ -hi \ ;,v ^-5 ^ U r-" •5 ^5 | /7„__ — — 1 24 1 s i 1 Fig. 33. — Diurnal Variation of the Wind at High Elevation. Pike's Peak, Colorado (see page 71). Fig. 34. — Average Hourly Velocity of Wind Estimated for Elevation of 100 feet above Surfaces (see page 71). Tornadoes. 73 prevailing directions are established by the continuous observation of the Weather Bureau for each locality. The prevailing direction of the local winds of the United States for January and July, respectively is shown in Figs. 35 and 36, page 74. From these maps the various monsoon effects of changes in temperature of the land and sea, due to the season, are well illustrated by the changes in the Eastern States from the prevailing northwesterly winds of winter to the prevailing southwesterly winds of summer. Table 2 gives the average number of storms originating in each dis- trict (see Fig. 27, page 65) annually during the period from 1883 to 1894. TABLE 2. Number of Storms Originating in Each District During the Years 1SS3-1894 District Average Annual Number of Storms Northern Pacific 18.4 Southern Pacific 2.3 Northern Rocky Mountain 9.9 Alberta 42.7 Colorado 12.5 Texas 10.9 Central '6.3 East Gulf 3.0 South Atlantic 2.9 West Indies 4.4 Average Number of Storms per Year 113.3 42. Tornadoes. — The tornado is more liable to occur in certain parts of the United States than in any other portion of the world (see Fig. 37, page 75). These are storms of the smaller extent and of the most violent type, and in proportion to their size are the most disastrous. They are limited in extent to a width of from fifty feet to about a quarter of a mile and their path seldom exceeds fifty miles in length, whereas the great cyclonic storms which are continually passing across the country are often a thousand miles or more in diameter and their paths can frequently be traced from the Pacific to the Atlantic Ocean. The tornado may occur in any month of the year, but is more common during the period from March 15 to June 15. 6 They occur during the hottest portions of the day and are always associated with violent e Moore's Descriptive Meteorology, pages, 237, 238. 74 Winds and Storms. t I t ^^U^ — J t f N K, > \) x -i- Fig. 35. — Prevailing Direction of the Surface Winds of the United States in Januarys (see page 73). Fig. 36. — Prevailing Direction of the Surface Winds of the United States in Julys (see page 73). Tornadoes. 75 thunder storms, heavy precipitation and usually with hail. Tornadoes usually form in the southeast quadrant of low pressure cyclonic storms during conditions of great humidity and after a morning temperature of 6o° to yo°. They are believed to be the result of rapid local heating of the lower atmosphere, accentuated by southerly winds which create unstable conditions, most frequently resulting in the establishment of somewhat local circulation and consequent thunder storms ; but occa- Fig. 37. — Geographical Distribution of all Recorded Tornadoes in the United States frofn 1794 to 1881 (after Greely — American Weather). sionally there is created a limited vertical whirl which develops the great vortical energy of the tornado. Before the formation of the funnel cloud, which is characteristic of the tornado, the clouds have a greenish black appearance and appear to rush together with a great violence. The black funnel then appears,, drops lower until it reaches the ground surface, when it enlarges some- what, rises and sways from side to side and sometimes jumps a space and strikes the ground farther on. The destructive effect of the tor- nado seems to be occasioned both by the heavy wind pressure and the high vacuum which obtains at the storm center and which frequently causes walls to fall outward and buildings to explode, apparently from the outward pressure of the air within. While the conditions favor- able to the formation of tornadoes may be foretold, it is not possible 76 Winds and Storms. with the present knowledge to forewarn the communities -in the exact location where tornadoes may occur without falsely alarming many towns within the district which will be entirely free from such visits. In general, the country 300 miles southeast from the main cyclonic center is in the region of greatest danger. 7 43. Hurricanes and Typhoons. — Hurricanes and typhoons are more limited and more violent cyclonic disturbances than the normal cyclone Fig. 38. — Mean Paths of West Indian Hurricanes during different Months 1876 to 1911. Short arrows indicate tracks of greatest deviation from the mean, the numbers are the year of occurrence (after Garriott). (see page 78.) previously considered and result from a more perfect system of vor- tices in the atmosphere. The tornado and water spout are of the same character and differ only in more limited dimensions and more intense action. Apparently the deflecting force, due to the earth's rotation, is essential to the formation of the vortex motion which gives rise to cyclones and tornadoes, for no such storms occur in the equatorial belt, although convectional action is there most powerful. The tropical hurricanes and typhoons, which occur in considerable numbers along the polar margin of the equatorial belt, are generated at the time this belt has migrated farthest from the geographic equator. These storms do not occur far out in the open sea, as the powerful Milham's Meteorology, page 236. Hurricanes and Typhoons. 11 80° SO" 100° 110" 120° 130" Fig. 39. — Mean Tracks of East Indian Typhoons s (see page 78). 140° trade winds prevent an invasion of their territory, except near the land where the trade winds are weakened by temperature and topographic causes. The origin of hurricanes is probably due to the planetary cir- culation, modified by the rapid heating of the lower atmosphere, which rises and is replaced by a more dense stratum from above. This, under s Figs. 39 to 41 inclusive are taken from Cyclones of the Far East by Rev. Jos6 Algue\ 78 Winds and Storms. the proper conditions, causes an intense local circulation which creates secondary vortices of the tornado type. In the tropics these follow the general westerly motion of the trades, traveling along the margin of the belt in which they originate, until a weak condition in the west wind zone allows their entry into the regions of western variables. Such storms are exemplified by the West Indian Hurricanes (see Fig. 38, page j6), and the East Indian Typhoons (see Fig. 39, page yy), which occur chiefly in August and September. In the southern '-■'F 5 Tf ■F-J5 ..,: Tota/^± -eauency clc ni •s fe* -*^*' ' — ^ /; -': /' A- tphot m Jlun n r, "• •icai vs\ \\ Ian Feb Mar Apr May June July Aug Sept Oct Nov Deo. Fig. 40. — Mean Monthly Frequency of Tropical Storms. s Atlantic such storms are unknown and they are rare in the southern Pacific. In the northern Indian Ocean, on account of its relation to the land, the planetary system of circulation is greatly modified, but cyclones similar in type to the typhoons frequently take place in the Bay of Bengal. In the South Indian Ocean, hurricanes of similar origin are generated in March and April east of the Island of Madagascar. The mean monthly frequency of tropical storms is shown in Fig. 40, and the annual occurrence for each year from 1876 to 19 10 is shown by Fig. 41, page 79. The hurricanes are of greatest interest to the hydraulic engineer on account of their influence on rainfall and on harbor and land pro- tection in the areas in which they occur. 44. Hurricane Movements. — In Fig. 38, page 76, are shown the mean paths of West Indian hurricanes during different months from Hurricane Movements. 79 1876 to 191 1. On this map the short arrows represent tracks of storms of greatest deviation from the mean and for the year indicated. West Indian hurricanes are the most severe of any general storms that visit the United States and occasionally, on account of the tremendous winds, the heavy precipitation and the high tides and waves which accompany their advent into the country, cause great loss of life and properly. On the night of September 8, 1900, one of these storms of tremen- dous force reached the Texas coast near the City of Galveston and 1876 J878 7880 08Z J884 1886 /S88 1890 /89Z 7894 7896 7898 1900 19QZ 1904 1906 1908 /9/0 !Fig. 41. — Annual Frequency of Tropical Storms: A — West Indian Hurri- cane. B — Cyclones of Bay of Bengal. C — Typhoons of Western Pacifies (see page 78). caused a loss of over 6,000 lives and of about $30,000,000 in property in the City of Galveston alone. About fifteen years later, on August 17, 1915, a similar storm visited the same locality but with less serious results, largely on account of the precautions which had been taken after the tragedy of 1900 and the warning of the United States Weather Bureau. The loss in this storm, however, amounted to about 275 lives and probably more than $5,000,000 in property. In the interval of fifteen years between these two great storms no severe hurricane visited the Texas coast, except one that passed south of Gal- veston on July 21, 1909, which caused severe northerly gales and some consequent damages to structures along the shores near Galveston. As the tides were low no lives were lost. The path of the storm of 1915 80 Winds and Storms. -5° c3,C\ ^o v jj>s 5 ^^\V r^ 1 ■^ *\ ^ -4 yN^, I \P M \ "* o \J Lrr— -^\ Vi/V "jr ^\< ~v^ — ^ •kj^—jl *3 V\/ fc 'CkY / h$l^^ //C^— 5$( 1 N / M -B- A i i /( T % if - ■lJt~ / 1 /'J)0 / / [ ~^' Sr\ o /oyr--^^ „ fe^t^ r^-yi 3( ^o /3^ Is -^^//_^-^ ^~Vf v *- ~~^^l • L ^- / "' i\~ A <3 ^-lA <*> ^Sf- ^cxirv ^ \ ^)ib 1 ^^^^r-^-^^X-L^-^p^--^^^ ^ \ X VJ ^1/^^N^\ ^ IC^^^uy^C^ v. # IU^WaN AM-— J l\ - {^0\ A~^ciyf /V 1 / W \ P* ^ Vy ">^r*? e ^^ i 7^\_- r __ J l/j?* ; 9 i > ' ^ J^^Xu^^^'If / f^l^jAjS^ H^J^jlJ" yjlJ ( "l // */£>!/# 1 °J i JL-t^ s> ^T^-— ' — "^-~>K ^^3*3 '^j\j^ ° )S^r^—^) ~~ ~^3v v S^^^^ ^(^C^-^ -^ v<^<\ !V vi^ 1 ' ^ s ^ 3 § S* "^N ^u """ "I^T 7x' > V -t a!a o^-V *5^ wV^. v_/ 1 ; "^-t4 ) A^U^ S3 /\\j i ~7 /r —\ V * ft 7^VyC# ^-« / V 7 1/ 7/ r° /$% — ^N r-: — 4/^ V r rnfum SK t ~ 3^V ^ i y^i \\ (1 Mi ^ / / i \ Y Vn>^ Si 7-J- -./ /r H^t "5 // / _^// ' J l\ J ^~T\ ^/C v? Xc / ° . /\ /\,96Z r* / J ----^ 7 yyCmoTfy^ "V ^< /-.^ . ^ /ir Cold Waves. 8 and the barometric conditions which prevailed throughout the United. States for the period August 15-21 are shown in Fig. 42, page 80. Figure 43, shows the air pressure changes at Galveston and Houston, Texas, during this storm. On the map for August 21st are also shown the path of the September, 1900, hurricane and the path of the hur- ricane of September, 1909, which produced high water conditions near the mouth of the Mississippi River and caused a loss of about 350 lives and a loss of approximately $5,000,000. A similar hurricane also Au gu-5 1 16 August 17 — - ._ ' — ~. -_ ■\ ^ r») if X s / > .. / / \ 1 ' 1 \ 1 v. 1 / 30.4 30.2 30.0 29.8 29.6 29.4 29.2 290 28.8 28.6 28.4 282 6 a 10 XII Z 4 6 3 10 M Z 4 6 8 10 XII Z 4 6 8 10 M 8 ° Fig. 43. — Barometric Pressures in Inches at Galveston and Houston during Hurricane of August, 1915.9 visited the region of New Orleans on September 29, 1915, and oc- casioned a somewhat similar loss of life and property. 45. Cold Waves. — From the best available data it appears that the lowest temperatures in the Northern Hemisphere are found, not at the north pole, but in a belt that crosses the Continents between latitude 50 and 70° north, and that the lowest known temperature, — 90.4 , was experienced in Siberia in latitude 6y° 5' north. This cold belt, which lies next to the Arctic region on the south, is broken where it crosses the water surfaces of Behring Straits and the seas east of Greenland, and is also modified by the influence of the eastern atmos- pheric drift from the seas over northern Europe and over the western region of the American Continent. The principal track of high barometric centers in North America 9 Monthly Weather Review, August, 1915. Hydrology — 6 82 Winds and Storms. lies south of the 50th parallel and their passage disturbs the North American cold belt and draws southward masses of cold air that con- stitute the cold waves of the United States. These movements some- times reduce temperatures to — 40 or even — 6o° in the west part of the extreme northern portion of the Central United States, with a min- imum of — 63. 1 ° at Popular River, Montana 10 (see Fig. 44). The passage of these high areas frequently draws cold air far to the southward, and occasionally during a long term of years temperatures Fig. 44. — Minimum Temperatures in the United States. 10 are reduced to the freezing point even as far south as the southern lines of Lake Okeechobee in Florida. The barometric changes and the temperature effects due to advance of one of these cold waves which produces freezing in all of the Gulf States are shown in Fig. 45, page 83 11 which shows the temperature and barometric condition for each of the four days from December 26 to December 29, 1894. On the 29th the temperatures at several points in Southern United States were as follows : Mobile 16° Jupiter 24° Jacksonville 14° Tampa 19° Key West 44° 10 See Bulletin Q, U. S. Dept. Agriculture, Weather Bureau, "Climatology of the United States," by A. J. Henry. 11 See Bulletin P, U. S. Dept. Agriculture Weather Bureau, "Cold Waves and Frost in the United States," by E. B. Garriott. Cold Waves. 83 ^°e •£i2f , •m/ '-»r~ /^Ckw °°^ £j£rM V \ / ^g/T /-\ "°\ V^ ^ Yn ) y\ *o IV /HV—- °o\ (*\ i y \ /- \ ~Tn>; ^ ^ )''yr • v J* /ys^-. —i-lyy 'J ■^ 7 // \ \h~A-~ *' ~*^Z\-t^ fizyr^f \ i^Y'' / /K ,-^/> yyr— £09 / ?v^kL ImXj ■ ) '"f^y\^-^/ .rev ^ "VJj/ '/ ''/STST* ^-fer^ — ■ H~t^j€^ '^yj-'f 1 ■jO£/^S 30%^ "^^s^ r~*r <5 v {'(po/ Sis s . m p aj +j crt -u 7J Tj CU ->-> Pi t» y-iP^ 84 Winds and Storms. 46. Hot Waves. — The movements of barometric pressure centers as indicated in Fig. 26, page 64, represent average conditions from which great variations sometimes obtain. During the summer season periods of stagnation occur in the movements of these centers. When at such times a center of high pressure rests over the southern Atlantic Ocean, with low centers over the northern Rocky Mountain region or along the northern border of the United States, the pressure dis- tribution will normally produce high temperature conditions in the Mississippi Valley and the Atlantic States due to the southerly winds which cause a continuing flow of heated air from the Gulf of Mexico and Southern Atlantic over these regions. The series of maps, Fig. 46, page 85, show the conditions for July 1-4, 1901, and illustrate the pressure, temperature and wind conditions during an extreme hot weather period. It may be noted that at 8 A. M. on July 2, 190 1, the thermometer stood at 92 in Philadelphia, 90 in Baltimore and 88° in New York City. Figure 47, page 86, shows the maximum recorded temperature in the United States. 12 47. Hydrological Effects of the Winds. — A study of the character of the winds which occur in any locality is of importance to the hy- draulic engineer on account of their effect on both precipitation and water levels. These atmospheric movements transfer such vapor as may be taken up from bodies of water, moist earth areas or areas of vegetation and deposit them again wherever the conditions are favor- able for precipitation. The passage of atmospheric currents that have been relieved of their moisture, on the other hand produces evapora- tion and adds to aridity. Hence the normal and possible movement and paths of cyclonic storms and the resulting direction of the wind, together with the character of the surface over which the winds have passed, materially affect their rain bearing qualities. These conditions will be further considered in future chapters, as will also the subject of normal stream flow and the occasional extreme flood conditions to which they give rise. The direct effects of the passage of storm centers on the elevation of surface waters by wind tides and storm waves are also important mat- ters to engineers in charge of construction on or in the immediate vicinity of large bodies of water and will be considered in the next chapter. 12 See Bulletin Q, U. S. Weather Bureau, "Climatology of the United States," by A. J. Henry. Hot Waves. 85 -^ "^-l 5fg& cvi^^Pur S^%% ^ ^sP^^ §W^'/^ ^ Pe^^Qt ^^B32i^?U V N rv 5) ) ' ^^ —T^^L / £^SO k (T^" 1 ~/n^ = y^ A. ?i\lr \ SyA ( A i'n'TN f \^ Hi \lr / ? "TA^ v^^b=_XNA VlA^^^^^i / t "°\\y ( --£---_ 5$ ^Vt s=: ^i/1 -frrWt to* )\L7 ol vw—/' TyyK—f rE<~^i W rf^-n i ■ 1 -^ — \ x «/ — y\ S^ r-t^s pras^ 1 \ , /^ .s JMteH T^oiyMtf^liK^—Al ( ^K@\x yZ^ fej- » £ s=i~-i-> I'o y\^s r- V ^:f__i/~ ' t-IVTH i NX $ $ vs ~V^P^~ S vl VVJyTN? >P $J>^SS-^<£2ra£p^\ ^ . v , \?"\r y ^te&-- %l\ ^---y ) V\| nV3< [ l,-^'" 1 "^Viiii?^ Mf^ ^\fe^^ a \ / ^V:'l^^fe^ l\ K ~'~T^7 i~T fW ^J^^^^nLA- \Jb ^^^Q\ Kr^* : Kj*r ^^P^C^S^S ?Pr o^$£% -V^Stt2*C_ 1\ w>«^»- N >j'-\ ^^A»* ^7"V/|\Li? fwS/ ^3 % 03 K >> Wl ^2 Pi Sh a Pi •e - CQ CQ *% ■=£>/ J4 C^^fT\\ ', fr|=EEi Hi Iv^^h^i Xyjlj- ^^^^"^ 1/ X oL-^T'c' 1 \" / ~* ' \ ^vSii i^Lfvf "j-£XvK Or^ |yv/ / NT/^JM \ >C%^/^ htt\l r^CE^ / \ v O ?/ °o ^-i v« ovj3 ^^ V\ V V^rtA^ 3 ° c. t CO - 2&ii^v/~ ii ?rA o °9= s i s> ^HAm/^^-''^ ^S?=^ & ^■?7^ -^X^r^Vv r -ij"/ — ZSHTirt>-L r^" u oi — o °° °^, U, 3g\ fe^^fc/ l'X / J\\J ^) irj^^^<^ = '4\r CO 4^^^)r L -fiiY Q5 ~l > "^ T^ — ? 7 °o / /a^ r*S i: !eSr~. I / ^-i< ^y ^&Z^^ \i ^~- % 12 pq *J *H s 0J p d Pi fe o O S 0) 86 Winds and Storms. 48. Weather Forecasting. — The study of the preceding sections of this Chapter should give a fairly good idea of the basis of weather forecasting. The data from which the daily weather map is made are taken each morning at 8 o'clock, 75th meridian time, which is ap- proximately equal to 7 o'clock at Chicago, 6 o'clock at Denver and 5 o'clock at San Francisco. The various observers at some 200 stations in the United States and the West Indies, after taking the observa- tions for air pressures, temperatures, humidity, precipitation, wind Fig. 47. — Maximum Temperatures in the United States is (see page 84). direction and cloudiness, send these observations to Washington. Cer- tain important stations also receive observations from such other sta- tions as are required for local forecasting. In the Forecast Division at Washington, these data are assembled on various charts, including charts showing : 1st. Changes in temperatures during the preceding twenty-four hours. 2d. Changes in barometric pressure. 3d. Humidity of the air. 4th. Cloud areas. 5th. Air temperatures and pressure, velocity and direction of the wind, character and amount of precipitation since last reports, and cloudiness. 13 TJ. S. Weather Bureau Bui. Q, by A. J. Henry. Weather Forecasting. 87 On this chart, which is the general weather map familiar to the pub- lic,- isobars and isotherms are drawn, the former indicating the centers from and toward which the air movements must take place. From years of experience the forecaster knows : i st. That high and low pressure areas drift across the country from the west toward the east in periods averaging from three to four days each and at a speed of about 600 miles per day. The average speed of movement is about thirty-five miles per hour in winter and twenty- four miles per hour in summer, for the lows, and about thirty miles per hour in winter and twenty-two miles per hour in summer, for the highs. 2d. That the lows, as they drift east, bring warmer weather and often rain or snow, while the highs which follow will bring cooler and prob- ably fair weather. 3d. That occasionally there are periods of stagnation in the drift of the high and low areas, and that at such times there occur abnor- mal conditions of cold, heat or precipitation. 4th. That about forty per cent, of the storms come from the north- west and pass easterly over the Lakes and New England, usually pro- ducing but scanty rainfall. 5th. That about twenty-one per cent, of the storms come from the arid regions of the southwestern states and in their northeastward movement can usually be depended upon to produce considerable rain. 6th. That the most severe general cyclonic wind and rain storms in the United States originate in the West Indies, travel in a northwest- erly direction until they reach the South Atlantic or Gulf Coast, and then recurve to the northeast and sweep along or approximately paral- lel the Atlantic Coast, their path being determined by the position and intensity of pressure centers to the north. 7th. That under the known conditions that exist at the time of ob- servation the storm movements will in general follow well established paths and give rise to conditions in the next twenty-four hours that are fairly determinate. 8th. That at times accelerating forces, not indicated by the daily observations which are taken only at the bottom of the great air mass, develop unexpected energy, cause the pressure centers to pursue paths not previously indicated, or gradually dissipate the energy of the storm in a manner not foreseen in the previous daily forecast. After the data are duly correlated on the weather map, the fore- 88 Winds and Storms. caster notes the changes and movements in the air conditions during the preceding twenty-four hours, and from these data he estimates what the weather will be in the different sections of the country the following day. LITERATURE A Popular Treatise on the Winds, Wm. A. Ferrel, 1899. The Weather and Practical Methods of Forecasting It, E. B. Dunn, Dodd, Mead & Co., 1902. American Weather, A. W. Greely, Dodd, Mead & Co., Philadelphia, 1888. Annual Reports, U. S. Weather Bureau. Monthly Weather Review, U. S. Weather Bureau. Storms, Storm Tracks and Weather Forecasting, Frank H. Bigelow. Bulle- tin 20, U. S. Weather Bureau, 1897. Cyclones of the Far East, Rev. Jose Algu6, S. J. U. S. Weather Bureau, 1904. Climatology of the United States, A. J. Henry. U. S. Weather Bureau, 1906. Cold Waves and Frosts in the United States, E. B. Garriott. U. S. Weather Bureau, 1906. West Indian Hurricanes, E. B. Garriott. U. S. Weather Bureau, Bulletin H, 1900. Hurricanes of the West Indies, Oliver L. Fassig. U. S. Weather Bureau, Bul- letin X, 1913. Cause of Trade Winds, F. A. Velschow, Trans. Am. Soc. C. E. Vol. 23, 1890, p. 106. Presents views at variance with usual accepted theory. CHAPTER V HYDROGRAPHY 49. Ocean Currents. — The circulation of the water of the ocean is caused by the heating at the tropics and cooling at the poles, which induces a general surface motion poleward and a motion in the depth toward the equator which is more or less modified by the continental masses and irregularities and by the difference in the velocity of rota- tion of the earth at the equator and the poles. The results of these causes are ocean currents more or less restricted in the limits of their surface activity (see Fig. 48, page 91). The ocean currents have an indirect effect on the temperature and rainfall of the various land areas eastward of the courses in which they flow. The warm ocean currents on their poleward flow increase the temperature of the superincumbent atmosphere which in drifting eastward, warms the northwestern shores of the continents. As the cold returning currents wash the eastern shores they can have practically little effect on those shores, except through their modification of the tem- perature of occasional ocean breezes. The modifying effect on the land temperatures of the eastward drift of the atmosphere from the ocean to the land is well illustrated by Figs. 15 and 18, pages 50 and 52, showing the isothermal lines of the Northern Hemisphere for January and July, respectively. The lines on the west coast of both Europe and North America are carried northward, while those of the eastern shores of Asia and North America are carried southward. The latter effect, however, is not due to the cold ocean currents but is a result of normal continental temperatures, the effects of which are in fact extended far to the east- ward over the oceans by the normal atmospheric drift. The effect of the ocean currents is less marked in the Southern Hemisphere due to the greater amount of water area and the conse- quent greater regularity in the courses of the currents and to the fact that the greater water area tends toward a more uniform distribution of heat. 50. Lake Currents. — Various factors will create currents more or less distinct in inland lakes. Among these are : 1. The general trend of the waters toward the outlet. 2. The inflow of water from streams. 90 Hydrography. 3. The winds. 4. Variations in air (barometric) pressures on different portions of the lake. 5. Variation in temperature at different depths. ■ These factors normally result in : a. A main current toward the outlet. b. Surface currents due to wind and barometric gradients. c. Return currents due to the escape of water temporarily banked up by winds or by air pressure. d. Vertical currents caused by temperature changes. In general, the body of water of a lake is so large relative to its out- flow that the main lake currents are often obscured or reversed by winds and barometric effects. These currents are seldom so persistent and intense as to "assure the continuous passage of water, with any material it may carry, in a single direction although under certain cir- cumstances such conditions may obtain for the greater part of the time. The subject of lake currents is of particular interest and importance in the study of the distribution of polluted waters from rivers or sewers relative to water supply intakes from the same bodies into which such polluted waters are discharged. 51. Vertical Lake Currents.- — In temperate climates, except during the period when lakes are ice covered, the temperature of the surface waters varies with the mean atmospheric temperature. From the breaking up of the ice in the spring, the surface waters begin to increase in temperature until about midsummer, after which they begin to cool until they reach 32 ° : Fahrenheit in the fall with the freezing of the sur- face. On account of the greater density of water at 39. i° Fahren- heit, when the temperature of the* surface water reaches that stage it begins to sink allowing warmer or colder water to take it's place until there is an adjustment of the whole body of water in accordance with its density and so far as it can be affected by changes in density. In shallow lakes less than 20 feet in depth, this vertical circulation of water is continuous except when the surface is frozen. In large and deep lakes there is but little vertical circulation as water of maximum density rests on the bottom at all times. In lakes of intermediate depth there are two periods of vertical circulation namely in the spring and in the fall when the surface temperature changes through that of maximum density and also two periods of stagnation, namely during the summer and winter periods. This circulation is of importance relative to the Lake Currents. 92 Hydrography. temperature and quality of water supplies which are affected by these periods of circulation and stagnation.* 52. Tides. — A periodical movement of the sea water which is not primarily circulatory is caused by the attraction of the sun and moon. This movement, which is manifested as a progressive wave called the tide, takes place essentially simultaneously on opposite sides of the earth. The effect of the sun is about forty per cent, of that of the moon. Due to the difference in the differential attraction of those two bodies, when the sun and moon act together upon one portion of the earth's surface, the high or spring tides occur and the low or neap tides result from the sun and moon acting in opposition, each condi- tion taking place twice in each lunar month. The problems and con- ditions presented by the tides are of importance in many affairs, such as improvement of harbors and other coast work, determination of mean sea level datum, determination of the mass of the moon, rigidity of the earth and other geodetic research. The investigation of the problem of the tides is exceedingly com- plex, since the influence of many conditions must be considered. Thus the height and speed of progression of the tidal wave are affected by the laws of wave motion, and attraction and motion of the moon, the attraction of the sun, the rotation and revolution of the earth, the in- ertia of the mass of water, the viscosity of the water, the friction of the water against the bottom, the irregularity of contour of the bottom, the interference and reflection of the wave due to the irregular land masses and other conditions. According to the law of wave motion as shown by Prof. G. B. Airy, the speed of progression of the wave depends directly upon the depth of water when the length of wave fr.om crest to crest is large in com- parison with the depth, and is the same as that which a free body would acquire by falling from rest through a height equal to half the depth of water. This law is mathematically expressed as (l) v=vFd where v represents the velocity of propagation g represents the acceleration due to gravity d represents the depth of water The wave can theoretically progress in synchronism with the ap- parent motion of the moon only when the depth is more than thirteen *See Miscroscopy of Drinking Water, by G. C. Whipple, Chap. V; also The Temperature of Lakes, by Desmond Fitzgerald. Tid es. 93 or fourteen miles, and since there are no such depths in the ocean the wave is forced to lag behind the point which is under direct attraction of the moon because of friction on the bottom of the sea. This lag is further augmented by the inertia and viscosity of the water itself. Considering the great variability in contour of the bottom and the consequent changes in the amount of friction, it is easily understood that unknown and very complex factors are introduced into the prob- lem, and the influences are rendered still more complicated by the land masses which interrupt and reflect the wave. Fig. 49. — Range of Spring Tides in and near the Bay of Fundy. In the open ocean, the tidal wave is three or four feet in height. As a wave passes from deeper to shallower water, the increased friction tends to decrease the height of the wave, while the expenditure of the same amount of energy on the small mass of water conduces to in- crease the height, the total result being to produce a higher wave. Under favorable conditions, the increase in height is very pronounced. Perhaps the best example of the great range in tides caused by the peculiar relation and configuration of the land and the increase toward the head of an inclosed body of water is found in the Bay of Fundy. Figure 49, shows the range of the spring tides along the coast of Nova Scotia and the State of Maine, and the increased height toward the head of the Bay of Fundy, where an extreme of 50.5 feet is reached in Noel Bay, Minas Basin. 94 Hydrography. In the Gulf of California the rise of spring tides is about six feet at Alata near the mouth and thirty-one feet at the mouth of the Colo- rado River at the head of the Gulf. "In Bristol channel the rise of spring tides at the mouth is about eighteen feet, at Swansea about thirty feet, and at Chepstow about fifty feet." x Under certain circumstances, obstructions at the mouth of an estuary present a condition causing the tide to enter as one or more waves, Fig. 50. — Hangchow Bore at Harming on the Tsien-tang River, China.2 known as the eagre or bore. Examples of this state are furnished by the Amazon River, which the bore ascends in three great waves thirteen to twenty-three feet in height. Figure 50, from a photo- graph, shows the bore in the Tsien-tang River at Harming, . taken in 19 14. The crest of water was vertical and about sixteen feet in height, with a second wave four feet in height so close behind that it cannot be distinguished in the picture. The river at Harming is about a mile in width and the water continued to rise for thirty minutes after the crest had passed, finally reaching a height of twenty-eight feet. The wave traveled with a high velocity. In seven minutes after it could be distinguished on the horizon the wave had passed. 2 Thus it is seen 1 See Professional Paper No. 31, Corps of Engineers, U. S. A., p. 90. 2 Photograph and data furnished by Mr. E. C. Stocker of Shanghai, China. Tides. 95 96 Hydrography. that the height- and amplitude, as well as the speed of progression of the tidal wave, are subject to great variations and complications, be- cause of the many complex influences exerted by the great variety of existing conditions. These complications are so great as to prevent a. general solution of the problem of the progress of the tide. At any certain place the height and occurrence of the tides are pre- dicted with a considerable degree of accuracy after the data of ob- servations for a year or more have been collected and correlated. The accuracy of such predictions becomes more nearly exact as the more or less local influences of winds, configuration, etc., become of rela- tively less moment and the transit of the sun and moon bear more di- rectly upon the time of occurrence. The . computations entailed in- predicting the tides are now accomplished by a complicated mechanical device known as the tide predicting machine, the latest one of which provides for thirty-seven components. 3 Fig. 51, page 95, is a map reproduced from an article on "CotidaL Lines for the World," by R. A. Harris. 4 The lines on the map are sup- posed to represent the lines of simultaneous high water at each hour Greenwich time. Mr. Harris says : "It will be noticed that there are several points from which the cotidal lines for all hours seem to radiate, and so must be points where the range of tide is zero. These points and radiating lines are caused by the overlapping of systems, by progression due to secondary or de- pendent bodies of water into which a free wave progresses, and by the necessity of a gradual change between adjacent regions whose tides are not simpultaneous. * * * "It has been supposed that the tides of the ocean advanced westward around the globe, endeavoring to 'follow the moon in her apparent diurnal course in the heavens. A westerly progression was especially looked for in the southern areas where a continuous zone of water en- circles the earth. What have we in reality? A remarkable eastward progression in the Pacific Ocean due to the opening between Cape Horn and Graham Land forming a break in the rigid boundary which con- stitutes the eastern support of the South Pacific oscillating system." It is probably true that the tidal motion of the water in ocean basins is an eastward and westward swinging motion rather than a series of progressive waves as seems to be indicated by the map. 3 U. S. Coast and Geodetic Survey Tide Predicting Machine No. 2, by E. G.. Fischer, Eng. News, July 20, 1911. 4 National Geographic Magazine, Vol. 17, p. 303, June, 1906. Tides. 97 Numerous other examples of the profound effect of continental configuration upon the progression or height of the tidal waves exist ' y among some of the most striking may be noted the case of New York Bay. The high tide at the western end of Long Island is some three hours later than that at Governor's Island in New York Harbor. This condition is produced by two waves, one of which progresses around the eastern end of Long Island and the other up East River. The meeting of these waves produces such an effect that the time of high tide differs by as much as an hour for points within a mile of each other. Another case of complication is that of Lynn Canal, Alaska, near Sitka. This canal is about ioo miles in length and extends in a north- ward direction. The time of high tide occurs at the upper end at about the same time as that at the mouth. This occurrence is attrib- uted to reflection of the wave from the inner end. Table 3 gives the range in spring and neap tides at various impor- tant points throughout the world. TABLE 3. Tide Table. Range of Tides. AMERICA Spring. Neap. St. J ohns, Newfoundland 3.3 1.5 Halifax, Nova Scotia 5.2 3.2 Pubnico, Mouth, Bay of Fundy 12.0 8.9 Noel Bay, Minas Basin Head, Bay of Fundy 50.5 37.4 Rockland, Mouth, Penobscot Bay 11.0 8.2 Bucksport, Penobscot River 12.5 9.4 Bangor, Penobscot River 14.9 11.1 Boston, Navy Yard 10.9 8.1 Pleasant Bay, Cape Cod 4.1 2.9 New York, The Battery 5.3 3.4 Philadelphia, Pennsylvania 5.6 4.9 Washington, D. C 3.3 2.4 Old Point Comfort, Virginia 3.0 2.6 Cape Hatteras, North Carolina. 4.2 3.1 Miami, Key, Biscayne Bay, Fla 1.3 0.9 Key West, Florida 1.6 0.9 Tampa, Florida 2.9 1.4 Port Eads, Louisiana .2 .1 Galveston, Texas 7 .4 Havana, Cuba 1.3 0.7 Colon, Panama 1.1 0.6 Balboa, Panama 16.2 8.7 Maraca Island, Brazil 30.0 14.3 Entrance, Amazon River, Brazil , 14.3 6.8 Altata, Mouth, Gulf California 5.8 1.4 Hydrology — 7 98 Hydrography. TABLE Z.—Tide Table— Continued. Range of Tides. Spring. Neap. Mouth, Colorado River, Head, Gulf California 31.5 7.3 San Diego, California 5.2 2.3 San Francisco, California (Presidio) 4.9 3.1 Columbia River, Bar 7.6 4.4 Seattle, Elliott Bay 9.1 5.9 ASIA Nagasaki, Japan 8.4 3.4 Yokohama, Japan 4.8 1.9 Shanghai, China, Wusung Bar 9.2 4.9 Hangchow Bay, China 13.7 7.2 Amoy, China 15.6 9.8 Hong Kong, China 4.4 2.1 Bombay, India 14.2 11.2 EUROPE Aberdeen, Great Britain 12. 10. Avonmouth, Great Britain 38. 28. Belfast, Great Britain 9.5 7.5 Bristol, Great Britain 33. 23. Cardiff, Great Britain 36.5 27. Cork, Great Britain 12.7 10. Dover, Great Britain 18.7 15. Glasgow, Great Britain 12.2 9.2 Hull, Great Britain 20.7 16.2 Liverpool, Great Britain 27.5 20.2 London, Great Britain 20.7 17.2 Queenstown, Great Britain 11.7 9. Southhampton, Great Britain 13. 9.5 Bordeaux, France 15.5 12. Calais, France 21. 17.5 Antwerp, Belgium 16.7 Rotterdam, Holland 7. Hamburg, Germany 6.2 5.5 Christiana, Norway 1.5 Gibralter 3.2 2.5 MISCELLANEOUS Alexandria, Egypt 1. .3 Zanzibar, Africa «. 15. 10. Natal, Africa 6.5 3.7 Honolulu, Hawaiian Island 1.5 0.8 • Manila, River Entrance, P. 1 1.8 0.9 53. Wind Tides. — The directions and intensities of the winds have an important influence on tides, waves and consequent water ele- vations. The effects of easterly and westerly winds on the surface of Lake Erie, the longitudinal extension of which lies in the direction of the easterly path of storm centers (see Fig. 52, page 99) is to produce at times great variation in the surface elevation at the easterly and westerly ends of the lake (see Fig. 53, page 100) . 5 The intense winds s Bulletin J, U. S. Weather Bureau, "Wind Velocities and Fluctuations of Water Level on Lake Erie," by Prof. A. J. Henry. Wind Tides. 99 known as hurricanes and typhoons that occur in the West and East Indies, respectively, occasionally greatly endanger the safety of cities and farm lands which are exposed to such effects. The effects of the West India hurricane of 1909 on the elevation of the water surface in the lakes and bayous of southern Louisiana near the mouth of the Mississippi River are shown on Fig. 54, page 101. Much of the loss of life and property in the hurricanes of Sep- tember, 1900, and of August, 1915, at Galveston (see Fig. 42, page 80), and along the coast of Texas, was due to the high wind tides Fig. 52. — Map of Lake Erie. that were caused by the passage of these storms. The tremendous direct attack of the waves accompanying these high tides can be re- sisted only by the strongest class of masonry construction. The high waters in the interior rivers, bayou and lakes can often be overcome by levee construction, properly protected at points exposed to wave wash. In the storm of November 21, 1900, the wind at Buffalo attained a maximum velocity of 80 miles per hour and the lake level rose to 120 inches above zero while at Amherstburg, Ontario, near the western end of the lake, the water level reached a stage 33 inches below zero. 54. Seiches. 6 — Seiches are oscillations of the water surfaces of lakes above and below mean lake level. They have an amplitude of from a few inches to occasionally several feet, and are supposed to be occasioned by changes in barometric pressure. Small rythmic oscilla- s See Notes on the Hydrology of the Great Lakes, by P. Vedel ; vol. 1, Jour. Western Society of Engineers, p. 426 et seq. ; see also Enc. Brit, article on lakes. 00 Hydrography. tions of a few inches in amplitude frequently occur on Lake Superior within a period of about ten minutes ; on Lake Michigan similar oscilla- tions from the east to the west, with a period of about fifteen minutes, are frequently observed. The periods of these oscillations are too short for transition from shore to shore across the lake basins, but oscil- lations of longer periods and of greater amplitude have been observed 72 4-8/2 4 8 12 4 8 12 4 8 12 4 8/248/24 8/24 8/24- 8/24-8/2 Hour A/or 19 20 21 22 23 Day Fig. 53. — Wind Velocities and Water Level Fluctuations on Lake Erie, No- vember, 1900 (From Bui. J, U. S. Weather Bureau) (see page 99). between Milwaukee and Grand Haven where such oscillations have oc- curred eleven times in twenty-four hours. 7 These oscillations were extensively studied early in the nineteenth century in connection with the Swiss lakes. 8 Seiches of unusual height have occasionally been observed. One seiche was observed in Lake Geneva in October, 1841, which was seven feet high, and in Lake Superior, in I854, a seiche of unusual height was said to have left the St. Mary River nearly dry for about an hour. On August 16, 1886, a similar series of oscillations occurred in Lake Michigan, caused by an area of low pressure passing over the lake and continued for about 24 hours. An automatic gage record of the varia- 1 See Annual Report Chief of Engineers, U. S. A. 1872. s See Nature, p. 18, 1878. GUI.? Fig. 54. — Hurricane Tide Effects in Southern Louisiana, 1900 (from a map by Mr, A. M. Shaw, published by the U. S. Dept. of Agriculture) (see page 99). 02 Hydrography. tions in the lake level at Chicago on this elate was published in the report of the Survey of the Waterway from Lake Michigan to the Illinois River by Major Marshall. The curve shows regular 15 to 20 minutes oscillations the amplitudes of which are a few inches, but combined with these oscillations are others of a larger amplitude with a period of about 40 minutes. Twenty-six waves occurred in an 18 hour period, the greatest waves having an amplitude of two feet ten inches, the surface falling this distance in 15 minutes. The largest seiche in Lake Mich- igan occurred on April 7, 1893, and was noted simultaneously at Chi- cago and St. Joe, Michigan, rising to heights of from four to six feet. Fig. 55, 9 is the record of an automatic U. S. L. S. gage located at the head of the St. Clair River and at the outlet of Lake Huron, Datum Line ^Elevation 57767 feet above mean tide at New YorK. Fig. 55. — Seiches on Lake Huron. and illustrates the occurrence of seiches caused by barometric pressure changes on the southern end of Lake Huron. 55. Waves. — On account of the characteristics of mobility and vis- cosity a disturbance to any one of the particles of a body of water is transmitted to contiguous particles and thence to others more remote, causing ripples, oscillatory movements or movements of translation known as waves. The wave is a disturbance of the surface in the form of a ridge or depression and is propagated by certain forces which tend to restore surface equilibrium. In general the particles of water do not advance materially with the wave. Ripples are the smallest class of waves in which the surface ten- sion of the water is the principal motive force of restoration of the particles. Oscillatory waves are similar to ripples, except that the motive force of restoration is principally due to gravity. These waves always occur 9 From Report on the North and Northwestern Lakes, by Col. G. J. Lydecker. Appendix 111, Report of Chief of Engineers U. S. A. for 1900. Wave Motion. 1 03 in groups and are raised partly above and are partly depressed below the undisturbed water level. Waves of translation are wholly raised above or depressed below the undisturbed water level. Those raised above the general level are termed positive waves and those depressed below this level are termed negative waves. Such waves are propagated as a single hump or hol- low passing over the still water surface. In this wave there is not only a progressive movement of the wave form, but also a translation of the particles of water for a short distance in the direction of motion. Waves may be classified as wind waves, tidal waves or those produced by sudden disturbances, such as by earthquakes. The great waves sometimes caused by earthquakes are the most serious in the'ir destruc- tive effects but are too uncertain in their occurrence, extent and action to admit of investigation. 56. Wave Motion. — A ship at sea which encounters great waves moving at a high velocity across its course is not appreciably moved from its course but simply rises as the wave crest passes and then sinks in the trough which follows. Floating objects near the land rise and fall in the same manner as the wave passes, move in or out with the tide, or in the direction of local currents, showing that wave motion is quite different from the motion of the water in which it moves. "If a body floating upon the surface of the water be observed care- fully, it will be seen to rise, move forward, and sink when on the upper portion of the wave, and to continue to sink, move backward, and rise again when on the lower portion of the wave, but without appreciable movement in the direction of wave travel, except such as may be due to the action of wind or of currents. Each particle moves about its position of rest in a closed orbit, in a manner consistent with the move- ment of all other particles in the wave. How this is accomplished is shown in Figs. 56 and 57, page 104, which are modifications of Webers* diagram of an oscillatory wave; the particles moving in circular orbits in the same direction as the hands of a clock, and the wave advancing in the direction shown by the arrow, a, b, c, d, e, f, g, h, etc., Fig. 57, represent horizontal, and k, I, in, n, 0, p, a, etc., vertical filaments of water' in a state of rest. The positions of the corresponding filaments during the passage of a wave are shown in Fig. 56. In this figure the filament a is represented by the common cycloid, and all other hori- zontal filaments by prolate cycloids. The dimensions of the orbits of the particles decrease rapidly below the surface, as indicated by the limiting lines rx and rzv in the figure. 304 Hydrography. "Those particles which lie in the same vertical filament when at rest, arrive at the lowest point of their orbits at the same instant when wave motion is in progress, taking the position shown at q. When the wave advances, the filament takes successively the positions p, o, n, etc., the upper portion bending over toward the wave crest until at k, directly under the crest, it becomes vertical. After the crest has passed, the filament again inclines toward it until the next succeeding trough arrives, when it again becomes vertical. Fig. 56 Fig. 57. Wave Action. io '""When the wave occupies the position shown in Fig. 56, all parti- cles between the filaments xx' and nn f have motion in the direction of wave travel, and those between nn' and ii f in the contrary direction." "Shallow water waves" are those that occur in water of a depth less than half the wave length. In such waves the orbits of its par- ticles are elliptical instead of circular. In very shallow water the rellipse approaches a straight line in form." 10 57. Height of Oscillating Waves. — The height of a wave is the •vertical distance from its highest to its lowest point. Oscillating waves will attain their maximum only in waters of adequate depth and no -such wave will reach a height greater than the depth of water through which it passes. Mr. Thomas Stevenson established from numerous •observations a formula for the height of wave in feet relative to the "fetch" or distance in nautical miles 11 to the windward shore as fol- lows : (2) h = 1.5vT ^vhere h = height in feet / = fetch in nautical miles. 10 See Professional Paper No. 31, Corps of Engineers, U. S. A., by Capt. D. D. Ctaillard. 11 The nautical mile = 6,080 feet = 1.15 statute miles. Height of Waves. 105 It is .evident that the maximum storms may not come from the di- rection having the maximum fetch and that, therefore, calculations based on the maximum fetch are often greater than will be realized. It must also be noted that heavy rollers as they approach a shore are deflected by the retardation due to shallowing water and become more nearly parallel with the shore or even change their direction entirely through the influence of islands or headlands. As the height of waves seldom exceeds forty-five feet, there is evi- dently a limit to the influence of the fetch, which in this case would correspond to 900 miles, while the width of the ocean may be several thousand miles. From the previous chapter it is evident, however, that, as most ocean winds have a rotary direction, it is seldom that violent winds follow approximately a straight course of more than 900 miles. For short distances (of perhaps two miles or less) and violent squalls, Stevenson proposes the formula (3) h = 1.5Vf + (2.5 — v'fT Hawksley 12 determined by observation that the height of waves in feet, h produced in large reservoirs by the heaviest gales in England could be represented by a formula that reduces to (4) h = .025Vl where / = the fetch in feet, or (4a) h = 1.95Vf 58. Length and Velocity of Oscillating Waves. — The length of waves seems to be related to the fetch, but is independent of the wave height. Waves in the Atlantic are said to be 500 to 600 feet between crests, and in the Pacific occasionally reach 1,000 feet. Lieutenant Paris of the French navy found the ratio of length to height of wave -j— was on an average 39 in light seas, 21 in rough seas and 19 in heavy seas. In deep water the velocity of the wave is independent of the depth and is essentially equal to that acquired by a body falling through a height eight per cent, of the wave length and is given by the formula 13 /gl (5) v= / = V5.121 = 2.26V1 V 2tt Rankine states that in shallow water (i. e., water of a depth less than one-half the wave length) the velocity is equal to that of a body falling 12 Proceedings Inst. C. E., Vol. XX, page 361. is See "Wave Action" by Gaillard. 06 Hydrography. through a height equal to half the depth d of water plus three-fourths of the wave height h and is given by the formula 13 (6) v= /2g|— H V \2 (d 3h\ = 4.012 V 2d + 3h Gaillard found this formula to give results considerably in excess of the observed velocities. The agreement of the calculated with the observed height of waves is shown by Table 4. It should be noted that the storm observed may not have been the maximum storm which might be expected, hence the observed height may not be a maximum. TABLE 4. Comparative Observed and Calculated Wave Height. ™- u Fetch in Location. nautical miles. .375 .428 .641 .748 .916 . 1.086 1.3 1.923 Observed height. 1.5 2.3 2.0 3.8 2.0 3.0 1.8 4.5 11. 7.0 15.0 16.5 23.0 4.0 8.2 15.0 22.6 Calculated height by formula. (2) (3) (4) 2.6 1.2 2.7 1.3 2.8 1.6 2.9 1.7 2.9 1.9 3.1 2.0 3.0 2.2 3.4 2.7 9.7 5.0 16.2 13.6 24.1 4.5 8.2 19.3 30.0 *Duluth Basin *Duluth Basin *Duluth Basin *Duluth Basin *St. Louis Bay *Portage Lake Firth of Forth *St. Louis Bay *Stannard Rock 41.45 San Pedro Bay, Cal 15.64 Marquette, Mich 116.63 *Portage Break Water 82.50 *Duluth Canal 258.62 Clyde 9.0 Lake Geneva 30.0 Sunderland 165.0 Petershead 400.0 *Lake Superior. Cunningham also gives the following as the recorded height of waves in heavy storms : Lake Geneva 10 feet German Ocean 12 to 15 feet Mediterranean Sea 15 to 20 feet Bay of Biscay 25 to 30 feet Atlantic Ocean 30 to 40 feet Pacific Ocean* 50 to 60 feet * Off Cape Horn and Cape of Good Hope. A wave encountering a current in the opposite direction is increased in height ; so also is a wave advancing in a channel either of uniform depth and decreasing width or of uniform width and decreasing depth. The effect of decreasing breadth and depth is well illustrated by the 1* See "Harbor Engineering" by Cunningham. Oscillating Waves. 1 07 increase in the tide wave in bays and channels like the Bay of Fundy or the Gulf of California, where the rise in tide at the head is several times greater than the rise at the mouth. When a wave travels from deep water into water the depth of which is gradually decreasing, a change in form takes place. Due to fric- tion upon the bottom, the velocity and length of the wave decreases, while the wave height for a time increases. The front of the wave be- comes gradually steeper and the velocity of its lower portion decreases until the greater velocity of the particles at the crest carries them forward, and the crest falls over, breaking into a foaming mass of water. In such cases the wave is transformed from a purely oscil- latory to a wave of translation, and the forward motion of the parti- cles is equal to the velocity of the wave. Under these conditions the wave exerts its maximum power. The height reached by waves breaking against headlands and struc- tural or protecting works rises by impact to much greater heights than those estimated above. Cunningham gives the following observations on such waves : The Hague 75 feet Bell Rock 100 feet Eddystone Lighthouse 150 feet S. W. Coast of Ireland 150 feet The element of waves, often of greatest importance in connection with engineering works along the oceans and lakes, is the height to which they will rise above mean still water. For this height Gaillard gives the equation h h 2 (7) a = — + C 1 — 2 1 in which a is the height of the wave above mean still water, h the total wave height, / the wave length, and C is a coefficient, found to be about two for a mean depth of twenty-six feet in the Duluth Canal and believed to be constant for any particular location. 59. Energy and Pressure of Waves. — The total energy £ of a wave exerted throughout its entire length (in foot pounds) and for one foot in breadth is equal to h 2 (8) E = 81h 2 (l — 4.9 — ) 1* The maximum pressure P of a water jet impinging against a square foot of area is wv- (9) P = c 2g 1 08 Hydrography. in which w equal the weight of a cubic foot of water and c is a co- efficient having a maximum value of not exceeding 2. For sea water w is approximately 2g and c may be taken as 1.6; hence Equation 9 becomes (10) P = 1.6v 2 For breaking waves Galliard found that the velocity of the waves was increased by the orbital velocity of surface particles so that under these conditions the pressure would approximate (11) P = 2.3v 2 Galliard measured with dynamometer pressures as high as 2,370 pounds per square foot at the end of the Duluth Canal in Lake Su- perior. Cunningham gives the maximum pressure of sea waves actu- ally recorded by dynamometer as three and one-half tons per square foot. 60. Effects of Waves. — The effect of ocean waves depends upon the exposure of the location to extended seaway over which heavy windstorms sometimes occur. Professor G. B. Airy shows that in the open sea when the depth is great in comparison with the length of the wave, the motion of the water at considerable depth below the surface decreases in geometrical progression and at depths equal to the length of the wave is less than .02% of the surface movement. When, however the length of the wave is great in comparison with the depth, as in the case of tide waves, the horizontal motion is the same from the surface to the bottom. The perceptible agitation sometimes extends to depths of almost 100 feet. It is asserted by pilots and mas- ters of vessels that in times of storms off Nantucket Shoals the sea frequently leaves sand on deck, although the depths are from seventy- five to ninety feet. The presence of mud in the bottom is a clear indication of the ab- sence of wave action, as mud is readily eroded and washed away by such action. The absence of mud is not an indication of wave ac- tion as conditions may not have been favorable for its formation. In various lake harbors in the United States Galliard states that the mud bottom of the deeper water changes to sand at the following depths : Duluth, Minnesota Lake Superior 55 to 60 feet Chicago, Illinois Lake Michigan 40 to 45 feet Milwaukee, Wisconsin . . . Lake Michigan 40 to 45 feet Cleveland, Ohio Lake Erie : 33 to 38 feet Any construction or barrier exposed to the attack of waves must be strong enough to resist them and to withstand the energy developed Literature. 1 09 when the wave progress is arrested wholly or in part or its destruc- tion will ensue. The force of the waves is the most severe of any force of equal intensity to which a structure may be subjected, for as Galliard states it is exerted and transmitted in the following ways, viz. : First. — By static pressure due to the head of the column of water. Second. — By the kinetic effect of the rapidly moving water. Third. — By the impact of bodies floating upon the surface and hurled by the wave against the structure. Fourth. — By the partial vacuum due to the rapid subsidence of the wave, producing sudden pressure from within. The effects of these shocks may be transmitted through joints or cracks, first by hydraulic pressure, second by pneumatic pressure, and third by vibrations of the material in the structure. In the Wick breakwater, concrete blocks weighing from 80 to 100 tons and lying from five to ten feet below low water, were swept away, while eighty ton blocks lying ten to sixteen feet below low water were unmoved. At Coos Bay, Oregon, blocks of stone weighing over ten tons have been washed off the jetty above high tide by storm waves. LITERATURE OCEAN CURRENTS Ocean Currents, James Page. Nat. Geog. Mag. April, 1902. Origin of Gulf Stream and Circulation of Waters in the Gulf of Mexico, W. B. Sweitzer. Trans. Am. Soc. C. C, Vol. 40, 1898, p. 86. Reviews causes, course and velocity of current with discussions by others. Ocean Currents. Marine Engineering, Jan. 1903. Discussion of Trade Winds, Gulf Stream and construction of charts. Physical Geography of the Sea, M. F. Maury, Harper & Bros., New York, 1857. Geography — Structural, Physical and Comparative, J. W. Gregory. Ten pages on causes and effects of currents. Map of location and sources of currents. Theory of Tides, A. dePreaudeau. Eng. News, Dec. 25, 1886. Explains solar and lunar effects on retardation of tides. See also Proc. Inst. C. E., Vol. 86, 1885, p. 422. Theory of Tides and Prediction of Heights, E. A. Gieseler. Jour. Frank. Inst. March and October, 1885. Illustrated mathematical discussion of tides. Range of Tides in Rivers and Estuaries, E. A. Gieseler. Jour. Frank. Inst. Aug. 1891, p. 101. Discussion of ranges on east coast of United States. Theoretical Amplitude of Tidal Oscillations, L. DAuria. Jour. Frank Inst., Vol. 131, 1891, p. 350. Mathematical discussion. Also Jour. Frank. Inst.,. Vol. 123, 1887, p. 331 and p. 409. Hydrography. Yearly Tides, W. S. Auchencloss. Proc. Engr. Club of Philadelphia, Vol. 9, 1892, p. 343. Tides and Tidal Scour, Joseph Boult. Van Nostrand Mag. Vol. 28, p. 148, 1883. Observations and statistics on force of tides and tidal currents. U. 8. Coast and Geodetic Tide Predicting Machine No. 2, E. G. Fisher. Eng. News, July 20, 1911. Description of the latest computing machine for predicting tides. Effect of Wind and Atmospheric Pressure on Tides, P. L. Ortt. Proc. Inst. C. E., Vol. 129, 1897, p. 415. Also Nature, May 27, 1897. Limitation of the Present Solution of the Tidal Problem, J. F. Hayford. Proc. Inst. C. E., Vol. 138, 1898, p. 535. Also Science, Vol. 8, p. 810. Dis- cussions as to methods of study, partly theoretical. Atlantic Coast Tides, M. S. W. Jefferson. Nat. Geog. Mag. Dec, 1898. Tide Phenomena at Galveston, H. C. Ripley. Trans. Am. Soc. C. E., Vol. 25, 1891, p. 543. Data and discussions of effect of jetties. Tide Indicators, Vidal & Kauffman. Proc. Inst. C. E., Vol. 164, 1905, p. 458. De- scription of apparatus. Tidal Instruments, Sir Wm. Thomson. Proc. Inst. C. E., Vol. 65, 1880, p. 2. Illustrated description of instruments. Indicating and Recording the Tides, D. A. Willey. Sci. Am. Apr. 12, 1902. Illustrated description of instruments. Pacific Coast Tides and Determination of Mean Sea Level, W. P. Dawson. Eng. News, June 28, 1916. Discussion of subject on west coast of Can- ada. Practical Manual of Tides and Waves, W. H. Wheeler, Longmans, Green & Co., London, 1906. Tidal Researches, Wm. Ferrel, U. S. Coast Survey, Separate publication, 1874. Cotidal Lines for the World, R. A. Harris National Geog. Mag. Vol. 17, p. 303, 1906. Force and Action of Waves, J. G. C. Curtis. Proc. Inst. C. E., Vol. 6, 1847, p. 127. Discusses proper form of sea walls. Force of Waves: Sea Walls near Edinburgh, W. J. M. Rankine. Proc. Inst. C. E., Vol. 7, 1848, p. 187. Observations of the effect of wave force. Movements of Waves, J. H. Muller. Proc. Inst. C. E., Vol. 21, 1861, p. 470. Practical details of works to resist waves. Wave Action in Relation to Engineering Structures, Captain D. D. Gaillard. Professional Papers No. 31, U. S. Army, 1904. Abstract in Eng. News., Vol. 53, p. 189. Wave Impact on Engineering Structures, A. H. Gibson. Proc. Inst. C. E. Vol. 187, 1912, p. 274. Report of investigation and conclusions. The Proper Profile for Resisting Wave Action, Robt. Fletcher. Trans. Am. Soc. C. E., Vol. 36, 1896, p. 514. Discussion of different types of sea wall profiles. Practical Manual of Tides and Waves, Wheeler. Descriptive treatise on waves and wave action. Longmans & Green & Co., 1906. Literature. 1 1 1 'Theory of the Water Wave, Morton F. Sanborn. Trans. Am. Soc. C. E., Vol. 71, 1911, p. 2S4. Conclusions from study of vertical circulation of water. Littoral Movements of Neio Jersey Coast with Remarks on Beach Protection and Jetty Reaction, Lewis M. Haupt. Trans. Am. Soc. C. E., Vol. 23, p. 123, 1890. Discussion of velocity and action of waves. Nature of the Tidal Wave, A. Cialdi. Proc. Inst. C. E., Vol. 47, 1902, p. 365. General discussion of subject. Tidal Waves and the Mascaret, E. S. Gould. Van Nostrands Mag. Sept. 1884. Mathematical review of paper in the French, discussing tidal waves, bore, etc. Ocean Waves and Wave Force, Theo. Cooper Trans. Am. Soc. C. E., Vol. 36, 1896, p. 139. Discussion of theory and results of investigation. A Resume of our Present Knowledge of Wave Motion. Scientific Am. Sup. Nov. 19, 1887. Memoir an the Experimental Study of Waves, M. L. R. Bertin. Van Nos- trand Mag., Vol. 8, 1873, p. 491. Discussion of relation between theory and actual results. Tidal and Storm Waves, W. H. Wheeler. Engr. London, Apr. 17, 1903. Con- siders causes of abnormal solitary waves. Progressive and Stationary Waves in Rivers, Vaughn Cornish. Engineering. July 26, 1907. Discussion of flood and tidal waves. Action of Waves as Affected by the Form of the Bottom, D. A. Stevenson. Proc. Inst. C. E., Vol. 46, 1875, pp. 7, 19. Explains increase in wave force due to submarine canyon. Excavating Power of Waves, South Coast of Ireland, G. H. Kinahan. Proc. Inst. C. E., Vol. 58, 1878, p. 281. Discusses transporting effect of waves and beach building. Magnitude and Telocity of Waves at Sunderland, J. Murray. Proc. Inst. C. E., Vol. 8, 1849, p. 200. Observations on height and velocity of waves. Telocity of Propagation of Waves, M. Laroche. Proc. Inst. C. E., Vol. 47, 1902, p. 363. Brief abstract from L. Academie des Sciences, Vol. 83, p. 74. Principles and Practice of Harbor Engineering, Brysson Cunningham, J. B. Lippincott Co., Phila., 1908. Notes on Geology and Hydrology of the Great Lakes, P. Vedel. Western Soc. Civ. Engrs., Vol. 1, 1896, p. 405. Illustrated discussion of climatology, fluc- tuations and geology. The Temperature of Lakes, Desmond Fitzgerald. Trans. Am. Soc. C. E., Vol. 34, 1895, p. 67. Illustrated discussion of lakes, and circulation in lakes. Lake Currents, W. H. Hearding. Jour. Asso. Eng. Soc. Vol. 11, 1903, p. 363. Effect of barometric changes in producing lake level fluctuations. Fluctuations of Water Level on Lake Erie. U. S. Weather Bureau, Bulle- tin J, 1902. Miscroscopy of Drinking Water, G. C. Whipple, Chap. 5, John Wiley & Sons, 1899. Sewage Disposal, Geo. W .Fuller, p. 280, McGraw Hill Book Co., 1912. CHAPTER VI ATMOSPHERIC MOISTURE AND EVAPORATION 61. Atmospheric Moisture — Tension and Weight. — The atmos- phere always contains moisture or water vapor which unless condensed as fog, clouds, etc., is transparent like the other components of the air. The maximum amount of vapor which can be contained in a cubic foot of space is limited by and increases with the temperature. At any given temperature a cubic foot of space or of air will hold only a cer- tain maximum amount of moisture, under which conditions it is said to be saturated. The weight of moisture contained in a cubic foot of space expressed in grains is termed the absolute humidity. The relative hu- midity is the percentage of saturation, complete saturation being ioo per cent. The amount of vapor in a cubic foot of space is independent of the presence of air except as the circulation of air accelerates or retards its formation. As moisture is received into the atmosphere a portion of the air is displaced thereby and the combined weight of air and vapor is less than the weight of dry air. A certain amount of vapor in a given space will possess a certain tension (or produce a certain pres- sure) according to the temperature. The weights of a cubic foot of dry air, of a cubic foot of saturated space, of a cubic foot of the air in a mixture of air and saturated vapor, and the corresponding weights of the mixture, together with the vapor tension and pressure of the air in a mixture of air and vapor are shown in Table 5, page 113, and the same relations of weights are shown graphically in Fig. 58, page 114. Vapor tension is not a measure of the total amount of water vapor in the atmosphere overhead, but indicates the amount of water con- tained in the air. For complete saturation the relations between the weight of moisture in the air (w), in grains per cubic foot, to the vapor tension (p) in inches of mercury at any given temperature (t) above the freezing point (32 F.) is given by the formula reduced from Regnault's experiments by Broch. 1 11.73 p (1) w = .9347 + .00204 t Below the freezing point vapor tensions do not agree with Regnault's experiments but have been determined by Marvin. 2 1 See Smithsonian Meteorological Tables, p. XXXVII. 2 See Smithsonian Meteorological Tables, p. XXXVI. Atmospheric Moisture. 113 TABLE 5. Weights of Air, Aqueous Vapor, and Saturated Mixtures of Air and Vapor at Different Temperatures, Under the Ordinary Atmospheric Pressure of 29.921 Inches of Mercury Weight of cubic ft. of Dry Air at Differ- ent Tem- peratures, Lbs. Elastic Force of Vapor Inches of Mercury MIXTURE OF AIR SATURATED WITH VAPOR. Tempera- ture Elastic Force of the Air in Mixture of Air and Vapor Inches of Mercury Weight of Cubic Fool Mixture op Air and OF THE Vapor Degrees Fahr. Weight of the Air. Lbs. Weight of the Vapor, Lbs. Total Weight of Mixture Lbs. .0864 .044 29.877 .0863 .000079 .086379 12 .0842 .074 29.849 .0840 .000130 .084130 22 .0824 .118 29.803 .0821 .000202 .082302 32 .0807 .181 29.740 .0802 .000304 .080504 42 .0791 .267 29.654 .0784 .000440 . 078840 52 .0776 .388 29.533 .0766 .000627 .077227 62 .0761 .556 29.365 .0747 .000881 .075581 72 .0747 • 785 29.136 .0727 .001221 . 073921 82 .0733 1.092 28.829 .0706 .001667 .072267 92 .0720 1.501 28.420 .0684 .002250 .070717 102 .0707 2.036 27.885 .0659 .002997 .068897 112 .0694 2.731 27.190 .0681 .003946 .067046 122 .0682 3.621 26.300 .0599 .005142 .065042 132 .0671 4.752 25.169 .0564 .006639 .063039 142 .0660 6.165 23.756 .0524 . 008733 .060873 152 .0649 7.930 21.991 .0477 .010716 .058416 162 .0638 10.099 19.822 .0423 .013415 .055715 172 .0628 ' 12.758 17 . 163 .0360 .016682 .052682 182 .0618 15.960 13.961 .0288 .020536 .049336 192 .0609 19.828 10.093 .0205 .025142 .045642 202 .0600 24.450 5.471 .0109 .030545 .041445 212 .0591 29.921 0.000 .0000 .036820 .036820 The ratio — is practically constant for small ranges of temperature but varies for temperatures from -20 c to ioo° F. as shown graphically in Fig. 59, 3 page 115. The relations of absolute and relative humidity to the temperature and weight of moisture in the air are given in Fig. 60. From this dia- gram the relation of absolute moisture to absolute or relative humidity at various temperatures can be determined. For example : if air at ioo 01 F. contains six grains of vapor, it is practically thirty per cent, saturated. If the temperature of the air falls to 72 F., the percent- age of saturation will reach approximately seventy per cent, and if the 3 The ratios of weight to vapor tension (Fig. 59) and the weights of sat- urated vapor per cubic foot of air (Fig. 60) are calculated by Formula 1 for temperatures above 32° F. and are taken from the tables of the Weather Bureau (Psychrometric Tables, Table XII, p. 83, by C. F. Marvin. U. S. Weather Bureau W. B. No. 225) for ratios below 32° F. Hydrology — 8 114 Atmospheric Moisture and Evaporation. temperature falls to 62 °' F. the air will be over saturated, the dew point will be passed and condensation will begin. When air is partially sat- urated and its temperature is reduced, the percentage of saturation will increase, and when the saturation reaches 100 per cent, the invis- ible vapor will begin to condense into visible moisture. Under these conditions the corresponding temperature is called the dew point. 02 Pounds /oer Cubic Fbor. 04 06 OS 200 \ \ nC \ ■p) \ $ \ ^ \ £ \ 1 \ t 0/ ^ \ § 1 1 $ \ 7 Si\ / <&A v \o 1 ■> 1 / S^C * 1 K 50 /OO 300 400 Grains per Cubic Foot. 500 600 Fig. 58. — Weight of Air and Saturated Aqueous Vapor at Normal Sea Level Pressure for Various Temperatures (see page 112). The dew point may therefore be defined as the temperature of the at- mosphere at which, with the amount of vapor it contains, it will be- come saturated. 62. Atmospheric Temperatures and Moisture at High Alti- tudes. — In general the temperature of the atmosphere at all seasons of the year decreases with the altitude (see Sec. 32), except at moder- ate elevations (below 10,000 feet) where atmospheric disturbances sometimes cause a temporary reversal of this condition (see Fig. 61, page 116). Fig. 62/ page 117, illustrates the temperature gradients as they commonly exist during summer (Curves 1 to 4 inclusive) and winter (Curves 5 and 6). The straight line numbered 8 shows the * See Bulletin Mt. "Weather Observatory, Vol. II, part 1, 1909, p. 4. Temperatures and Moisture. 115 adiabatic gradient for dry air and line 7 shows the temperature gradient for saturated air, starting with an assumed summer sea level tempera- ture of 68° F., while lines 9 and 10 indicate the same gradients for Fig. 59.- u 13 12 " /o o so eo /oo 40 60 -Ratios of the Weight of Vapor in the Atmosphere to Vapor Tension at Various Temperatures (see page 113). .00/ / = bor?o , £ per Cu6/c 002 Foo? 003^, 004 100 * y & & s* t$ ^ '0 u- •.;" ^ T22 oZ 9^ 80 -<; X?. "r^ H)& ^ -• fidiabatic •> ■■ Pru V \ \ i V T / i \ 1 i { «\ ft \ \ \ i* \ \ // 1 ■r \ i i l f / / J? > fa V / 4 yy / / # / / )* / Js / 37l I^S /, 7/ j£p /fo $r ./ & $\ / s # / / A 4o ■' / r j> A ?/ / / 7/ 9 / / f i /V f ft' I /> /[ 7 * \ / f \ /j> \ i IS V w \ 70 60 50 40 30 20 /O O -/O SO ~30 -40 SO -GO -70 SO 7~em / oerarure. fat?re/7/7eir Fig. 62. — Vertical Temperature Gradients in Free Air (see page 114). Atmospheric Moisture and Evaporation. 20 / j / / V^/ tf / V $ &L M M $7 M f $/ H I- / \° W t ' 4 4 fi/ t (V- r ^ S/ I $[.; ft \y ..yUf \i ^ 1 * / •> * n - 'it /§ k V /* i/f ij° 7(3 S3 50 ^(3 30 30 /(3 -10 -20 -30 Temperature -Fahrenheit Fig. 63. — Theoretical Temperature Gradient and Decrease in Mean Annual Temperature with Altitude (see page 116). 40000 36000 36000 34000 320OO 30000 X Z8000 .5 260OO ~*% 24000 ^tzzooo ^ZOOOO \ /8000 b 16000 ■S § /4000 < I20OO IOOOO 1 ; 1 » j|". 'I 1 ! A \\\ \\\ , \ \ \ \ \ \ \ \ \i? ^ \ >»\ \-t-."^ ^%j ^-, &-- s^ "-*--. "■■^ A t ^ ^ -N \ -*-*., \ 1 -r "s \ " -„ 6000 4000 zooo °0 I Z 3 4 5 Wafer Vapor - Gra/ns per Cub/'c fbor Fig. 64.— Vertical Distribution of Water Vapor on Clear Days (see page 119). Distribution of Atmospheric Moisture. 9 facts agree with the theory is made evident by Fig. 64, 6 where the actual vertical distribution of vapor for various seasons of the year is shown. The quantity of vapor in the atmosphere decreases with the increase in altitude more rapidly than the pressure decreases, as will be seen by reference to Fig. 65, in which the decrease in vapor tension and 30000y 25000 20000 •% /5000 /OOOO sooo O 20 40 60 60 Percent of ToM Pressure of>5eoL.eve/. Fig. 65. — Decrease of Vapor Tension and Pressure with Increase in Altitude. in atmospheric pressure is given in percentages of such tension and pressure at sea level. 7 Vapor tension is practically proportional to quantity of vapor, hence the diagram shows the relative vapor content of the atmosphere at dif- ferent elevations. About one-half the total moisture is contained in the atmosphere below an elevation of 6,500 feet, about three-quarters below 13,000 feet, and about nine-tenths below 21,000 feet. Hence on a clear day in winter with an absolute humidity of one grain per cubic foot at the surface of the earth, the total moisture in the atmosphere distributed over the surface of the earth would equal about .25 inches ;. while in summer with six grains of moisture per cubic foot at the sur- e See Bulletin Mt. Weather Observatory, Vol. 4, part 3, 1911, p. 128. 7 See Handbook of Climatology by Dr. Julius Hann. Translated by Prof. R. De C. Ward, 1903, p. 286. i 20 Atmospheric Moisture and Evaporation. Fig. 66. — Average Distribution of Atmospheric Moisture in the United States for January. (Grains of water per cubic foot of air) (see page 121). Fig. 67. — Average Distribution of Atmospheric Moisture in the United States for July. (Grains of water per cubic foot of air) (see page 121). Distribution of Atmospheric Moisture. 21 face, the total atmospheric moisture if so distributed would equal about 1.5 inches. 63. Geographical Distribution of Normal Atmospheric Mois- ture. — The moisture of the atmosphere is the result of vaporization from water surfaces, from vegetation and from other moist surfaces and is therefore usually found in greater absolute and relative quanti- ties near the sources from which the moisture may be derived. On Fig. 68. — Average Annual Relative Humidity in the United States (percent- age). the ocean in the Doldrums the air is always near saturation. This is due to the Trade Winds which, flowing over the warm surfaces of the ocean with slowly rising temperatures as they advance, are continually supplied with vapor and maintained in an almost saturated condition. Over the deserts where the supply of moisture is very small the quan- tity of vapor in the atmosphere is far below its capacity. In general, the amount of moisture decreases toward the center of a continent, but this is modified by normal rainfall conditions, by the presence of large lakes, extensive forests and swamps and by prevailing wind move- ments. The average distribution of atmospheric moisture in the United States in January and July is shown in Figs. 66 and 6j respectively, page 120, and the average annual relative humidity in the United States in terms of percentage of saturation is shown by Fig. 68. 22 Atmospheric Moisture and Evaporation. 64. Variation in Absolute and Relative Humidity. — Absolute hu- midity will vary at every locality from hour to hour and from day to day with atmospheric temperature, pressure, wind movement and re- sulting evaporation. Relative humidity will vary to a still greater ex- ■RELAT/VE HUM/D1TY r \ k y- \ n aP ^ ->"N k / \ h K ~Z V J v> /v /' \ I \ V *- p? r V V rz ( \ / K \ / \ LZ \y \ / ^60 \ s \j f \ J f 40 1 V 1 V TEMRERA TURE X *~\. •*"> A / > \ > / \ l\ r v \ / V L / \ J a / L y v / / "V / /V^ \ A / v. r^ ^ ^J f J \- -w' ► "«— ^ ' fiO ■ — . s ^ ABSOLUTE HUM/ D /TV %/2 » 1 $0 / / \ is 1 I- ; V A / \ /\ / RAINRALL 76/£6/*76/a6M6/2 6M Aug.2. Aog.3. Aug 4. Aug 5 Aug 6. Fig. 69. — Relative Humidity, Temperature, Absolute Humidity and Rainfall from Midnight, August 1 to Midnight, August 6, 1916, at Madison, Wis.* tent, as with the same moisture content the degree of saturation will vary with the hourly variations in temperature. Both absolute and relative humidity will vary in still greater degree in different localities. The variation in temperature and both relative and absolute humidity from hour to hour at Madison, Wisconsin, for the period August i to 6, 1916, are shown in Fig. 69, page 122. The amount of precipitation during this period and the consequent changes in atmospheric mois- ture during this period are of interest. The variation in absolute hu- midity from month to month at various typical stations in the United States is shown in Figs. 70 and 71, page 123. Compiled from data furnished by E. R. Miller. U. S. W. B. Sources of Atmospheric Moisture. 123 65. Interchange of Moisture Between Air and Land or Water Surface. — The moisture of the atmosphere is furnished by evaporation from water surfaces which cover nearly three-fourths of the earth's surface. The oceans, lakes, swamps and river surfaces, therefore, furnish the largest portion of atmospheric moisture. Additional sources are the ground surface, which is usually somewhat moist, and the transpiration of plants and animals. Vegetation through its roots, which often penetrate the soil to considerable depths, draws from the ground storage moisture which would otherwise remain as ground water. It is apparent that the wind will carry some of the vapor from i 8 •3 O ^t Jan Feb Mar. Apr. Mai/ Jun Jul fluq Sept. Oct Nov Dec Fig. 70. — Variations in Average Ab- solute Humidity at Various Sta- tions (see page 122). 0\ nr •■:e *>- v $/ ^10 \8 I r !« <§ Jan Feb. Mar Ppr Mau Jun Jul fiuq. Sept. Oct. Nov. Dec. Fig. 71. — Variation in Average Ab- solute Humidity at Various Sta- tions (see page 122). 1 aw — ' & v) ffi ^x; 2£2-~ [ j/y$ s in Franc tis yy^> <^ the continent to the sea and some of the vapor from the ocean to the adjacent continents. Bruckner s has estimated that the net results of this interchange of vapor between the oceans and land is that only seven per cent, of the precipitation of the land comes from moisture received directly from the sea. The author believes, however, that this estimate is too small. The moisture of the air over continental areas is most largely drawn from the inter-continental water surfaces of lakes, swamps, marshes and streams, from moist earth areas and from the transpiration of forests and other vegetation and probably does not receive more than from twenty-five per cent, to thirty-five per cent, from the oceans. (See Table 13, page 165.) Evaporation is continually taking place from a moist surface when- ever the water is above the dew point temperature of the air which is in contact with it. Whenever the water or other surface in contact with moist atmosphere falls in temperature so that the air in contact is reduced in temperature below the dew point, condensation occurs s The Relation of Forests in the Atlantic Plain to the Humidity of the Cen- tral States end Prairie Regions, by Dr. Raphael Zon. Science, Vol. 38, p, 69. 24 Atmospheric Moisture and Evaporation. and dew is formed on the exposed surface. There is therefore a con- stant exchange of moisture between the air and moist surface, some- times by evaporation from the water to vapor and sometimes by con- densation from vapor to moisture. The observed evaporation from water surfaces is the net result of this interchange of moisture. 66. Heat Changes Involved in Evaporation and Condensation. — As water increases in temperature it must absorb heat, as in the case 3000 zaoo tZ600 M Z400 \ZZOO -8 ^ 2000 | 1800 \l600 %I400 \ ^1200 k/ooo zoo o Ms/finq fblnt 1 MeUing\ Paint. \ / r / / a / »5 7 / f \ / , / ■A f / , / '/J i ' W i i , t 1 ,.<■ *y b 5 -4- ?w u T^ - 2540 2340 2140 1940 1740 1540 % 1340 \ 1140^ 940% 740 %■ 40O 300 /zoo mo Heof, Brifish Thermal Unih. 540 340 2/Z 140 3Z -260 -460 K. Fig. 72. — Relations of Heat Energy in Water.* of all other bodies. When however water changes its physical form from solid (ice) to liquid (water) or from liquid to vapor, a large amount of heat is absorbed and becomes latent. The heat necessary for the increase in temperature through a wide range is shown by Fig. 72, page 124. In this diagram the amount of heat required to raise the temperature of water is compared with the amount of heat necessary to raise the temperature and to melt gold and steel. The latent heat of melted ice and of vaporized water, which is not manifest by an increase in temperature, is shown by the horizontal lines of the diagram. From this diagram it becomes evident that when water is evapo- rated, a considerable amount of energy must be absorbed from some source. This energy may be obtained by the reduction of temperature in the water itself or of the body in which it is contained or by radiant energy from the sun or from adjacent bodies. In the same manner Lecture by G. H. Babcock. Sci. Am. Sup. Dec, 1887. Heat Changes in Evaporation and Condensation. 1 25 condensation is accompanied by a transformation of latent to percep- tible heat which is delivered to the atmosphere and has an important effect on the dynamics of storms. Dew and frost are caused by the radiation of heat from the earth's surface into a clear atmosphere, the reduction in the temperature of the adjoining air below the dew point, and consequent condensation. Low foe"s are the result of a similar radiation and reduction of tern- Fig. 73 — Relative Annual Evaporation from Free Water Surfaces in the United States. perature in the lower atmosphere. High fogs and clouds are the result of dynamic cooling due to expansion of rising vapors. The condensed particles of moisture which make up clouds and fogs are very small, varying from .ooi to .00025 inch in diameter, and they are maintained in suspension in the atmosphere by ascending air currents. As a drop of water .001 inch in diameter would fall at the rate of less than two inches, per second, 9 it requires a feeble upward current to maintain it in suspension. 67. Evaporation. — Evaporation takes place from moist surfaces and from the water surfaces whenever such surfaces are in contact with unsaturated air. Fig. 73, is a map showing roughly the annual evaporation which takes place from water surfaces at various points within the United States. This map and the table of monthly 9 See Meteorology, by W. I. Milham, 1912, p. 232. 1 26 Atmospheric Moisture and Evaporation. evaporation in the Appendix are taken from data given in the Monthly Weather Review of September, 1888. The Weather Review observa- tions were deduced from readings of dry and wet bulb thermometers as observed at various signal Service Stations in 1887 and 1888. These deductions were supplemented by observations at several sta- tions by means of the Piche evaporimeter. This map (Fig. 73) shows the annual evaporation rates in the greater portion of the United States to be equal to or greater than the local annual rainfall. The total annual evaporation as shown by the map is, however, based on free water surfaces only, and evaporation from ground surfaces .takes place only from occasional moist surfaces which exist after rains. While evaporation, like rainfall and other meteorological phenomena, varies from year to year in accordance with the variation in the con- trolling factors, yet this variation is apparently much less than the variation in most other meteorological phenomena such as rainfall, temperature, etc. This map and the table therefore indicate relative conditions at the various stations and roughly the evaporation from free water surfaces. The comparative monthly evaporations at sixteen stations distributed throughout the United States, and based on these tables, are shown graphically by Fig. 74. At a number of places in the United States evaporation observations have been made for a number of years and from the data thus collected a general knowledge of local variations that occur in evaporation can be obtained. 10 When the amount of evaporation becomes an important element in engineering problems, a study must be made in detail of the local conditions which modify its distribution and total amount. 68. Factors of Evaporation. — Evaporation at any time or place will depend on various physical and meteorological conditions most of which will vary from time to time. The meteorological conditions frequently vary with considerable rapidity from hour to hour (see Figs. 21, 32 and 69). The principal meteorological factors are: vapor ten- sion, temperature and wind movements in which the variations are con- siderable and cannot be forecast with any degree of certainty, except as to monthly average which can be foretold only within certain rather definite limits. In consequence these factors must be considered broadly for practical purposes. The physical factors to be considered are : altitude and nature of the surface from which evaporation occurs, and the subsurface so far as it affects the amount of evaporation. In general, the surface condi- tions may broadly be divided into land and water surfaces. 10 See Literature at end of chapter. Factors of Evaporation. 27 Dec Jan DecJan Dec Jan Dec North Atiantic New Haven Connecticut South At /ant, Austista. Ga St Lawrence Onto ffiver Detroit. Mich Cincinnati. Ohio Jan Dec Jan Dec Jan Dec Jan Dec Missouri Driver Topeka. h(an Heiena. Mont F?ed Ffiver Mooreheaa'. Minn North facific Oiympia. Wash Jan Dec Jan Dec Jan Dec Jan Dec Co/umbia /-fiver South D^acific Co/oraaio Driver Great Gas/'n 3/Dokane. Wash Dacramenfo. Ca/ Yuma. Ariz. Winnemucca. Nev Fig. 74. — Monthly Evaporation from Free Water Surface at Sixteen Stations in the United States (see page 126). 1 28 Atmospheric Moisture and Evaporation. The body of water from which evaporation takes place may be small or large, exposed or protected from the wind, it may be shallow or deep, it may be free or filled with more or less vegetation. If exposed to wind movements, if small, shallow or filled with vegetable growth, evap- oration will be increased. In the summer when evaporation is at a maximum more water will evaporate from small and shallow bodies than from deep and large bodies on account of the increased temperature in the small bodies of water. The presence of vegetation will also add to the amount of water loss as evaporation will be augmented by the trans- piration of the growing plants. Evaporation from ice surfaces while comparatively small is still a factor not to be ignored. The evaporation from land surface normally depends upon the amount, intensity and distribution of the rainfall and also on the moisture conditions of the surface. Light rains may be evaporated from the surface while much of a heavy rainfall will percolate into porous soil beyond the reach of evaporating influences. Land surfaces may be saturated, moist, dry, frozen or covered with snow or ice. They may be of loam, sand, clay or rock of varying characters and underlaid with various materials in endless varieties and of varying porosities. The surface may also be bare or cultivated ; it may be covered with crops of various characters ; it may be grass land or forests. The exposure to winds is also important. It is evident that comparatively more evaporation will take place from wet than from dry land and that in the latter case no evaporation will take place unless the capillarity of the soil or the roots of plants draw the water from lower levels. It is apparent therefore that the whole question of evaporation from any drainage area is a very complicated subject that can be ascertained with no great degree of accuracy but which nevertheless must be in- vestigated and understood so far as practicable in order that many im- portant problems of hydraulic engineering may be solved with as great a degree of certainty as the conditions permit. 69. Vapor Tension. — The rate of evaporation at any time depends not on the relative humidity which varies rapidly with atmospheric temperature, but on the vapor tension due to the temperature of the water surface (V) and the vapor tension in the layer of air in contact with the water surface (v). If this difference be large, evaporation will be rapid, while evaporation will decrease with the difference and will change to condensation when this difference is negative (see Fig. 75, page 129). Vapor Tension. 129 Just how these vapor tensions should enter into a correct formula for evaporation has not yet been accurately determined, although a number of such formulas have been proposed. The experiments of b 8 • \ 5)) o 1 1 8 • o/ s£ • 'Si o° /f Q S0 so / / —/- *f' / 5/ 4' ' if\ A/r //7 5ur? - r ■P- VVarerjCL'. Tonk--^ \ \ \ ^N \ / 2 7 JO 3-456 7~/rr>e JD&ys Fig. 76. — Average Daily Temperatures for Ten Consecutive Days, beginning August 24, 1905, at Arlington Heights. ture variations relative to exposure in sun and shade and between moist and dry soils are shown in Fig. y6. lz The waters of lakes, reservoirs and canals, in which the determina- tion of the amount of evaporation becomes of importance to the en- gineer, are in general exposed to the sun and weather, and while their temperatures do not vary hourly and daily directly with the tempera- ture of the air, there is a more direct relation between the average monthly temperature of air and water in any locality. The investigations of Dr. Fortier 14 do not indicate any constant re- 13 Bulletin 177 U. S. Dept. Agriculture, Evaporation Losses in Irrigation, by Dr. Samuel Fortier, p. 42, Fig. 17. 14 ma. Temperature. 13 too *§ 90 S> 80 I 40 30 o o . fi JOO ^.90 Si S 60 I ! ^ 40 30 „ y s°o o r^ O 2 4 6 6 /O t2 /4 £vcrpor-0'//os? J //7c/?es per /for?r/? SerAe/ey, Co///br/7/a 100 . . 30 \ $ 70 \50\ K AO 30 o o t> , /i 6 } 6> / s Q ' o 2 4 G 8 /O 12 14 f'voporof/o/? /r?c/?es per fflorrrfr r^Of7?or?cr C&//for/7/a O 2 4 6 8 /O /2 /4 {Tyt3po/-0'r/Gr?, //?c/?es joer Man//?. Ch/co. Ca//forn/a /OO 90 i ISO I 70 t \ 60\ I k 40 30 /OO 1 \"> \?o K 40 30 o o f o c o o I r?. //7c/?es per A7o/?rh Ccr/ejr/co. G <&y /(s^ *p yy «& M V r . ^-ku pr iw ^ w$& 'X*r\ atfPZZ&se* h^ *!bji£ $s, i&x ps N^ SO 30 90 100 40 50 60 70 QO Wean A y 7o/7/ , /?/y Temperas are, r~a/?r-e/7h&/r Fig. 79. — Relations between Mean Evaporation and Temperature at Various Stations (see page 132). atmospheric pressure ; hence at a given temperature evaporation should increase directly with the reduction in barometric pressure, due to al- titude. In Fig. 82, page 137, the theoretical evaporation at various eleva- tions is shown relative to sea level under similar conditions of (mean monthly) temperature, wind and humidity, in accordance with the above law. On this diagram is platted the increase in evaporation with altitude and constant temperature of the station previously con- sidered in Fig. 81. The discordant results indicate that the wind movements or relative humidity at the higher altitudes have had a de- cided accelerating effect on evaporation. 73. Evaporation of Snow and Ice. — Snow and ice exposed to at- mospheric agencies decrease in volume by sublimation due to the same 136 Atmospheric Moisture and Evaporation. SI o t.5 ZO 25 Depth of Weekly Evaporation -Inches Fig. 80. — Influence of Altitude on Evaporation on Eastern Slope of Mount Whitney, Cal. (see page 133). 5O0O — 40 50 ■ r 60 V ~7C J- ■80 ^■fl/boguergue 7 \ L 1 j t ,v i -60iL 70fi SO .Elephant Butte. 4000 1 _ \ ElPaso SO* 60 '• 1 70°- do 90°' p / \30OO 1 / ■50° / ecfi <90"j Si % Carlsbad / r -vl / r « S / j / \zooo 1 I / / * 1 / / £ / / $ 1 / 1000 l£0°—t 'SO' ' ' re* •[ t/G v'jr ^bus. Ohio. 50° 60° ,%o nenasha, Ufa Up j 70° 6V° 30°""\"'"'' """** 1 1 L * ' • d 7sfon. Efass 2 4 6 8 tO 12 14 Depth of Monthly Evaporation /n Inches. Fig. 81. — Relations between Evaporation and Temperature at Various Alti- tudes (see page 134). factors which cause evaporation from moist land and water surfaces. With the thermometer below the freezing temperature, the wind is ap- parently the greatest factor in this phenomena. The information on this subject is fragmentary and the loss difficult to determine on account Evaporation of Snow and Ice. 37 of varying conditions even within limited areas. Fitzgerald 20 found that average evaporation from snow was 6 inches per month and con- cluded that evaporation from ice is nearly twice as rapid as from snow, and might equal six inches per month with a 12-mile wind. Lee 20 es- timated the loss from snow field on the highest mountain areas (the Sierra Nevadas) at y.y inches (of water) per season. Lippincott' 1 estimated the season's loss on the high mountains of the San Bernardino Valley at 14 inches of water. Baker' 2 made various experiments at A> dOOO 6 6000 ijj 4OO0 / / 1 1 \ / / / 1 f / / 1 ' / f \ / / / / 1 / / / / / / 1 1 / / f 1 / / 1 1 / / h \ ! 1 ' '/ r'/ / / y :' \ / / / / , '[' ■ \ / / ' \ / / 1 ' \ O 2 4 6 8 !0 12 /4 16 18 20 22 Depth of Month 1 1/ Fi/aporaf/o.i in Inches Fig. 82. — Relations between Evaporation and Pressure (see page 135). the Utah Experimental Station which are shown relative to the simul- taneous temperature in Fig. 83, page 138 on which are also plotted Lippincott's observations, all reduced to monthly rates of evaporation. The wide departure from a curve drawn through the centers of gravity of the various groups of ten points shows the influences of wind, vapor tension, etc. The effect of forests in decreasing sublimation seems largely to be 20 Evaporation, by Desmond Fitzgerald. Trans. Am. Soc. C. E., Vol. 15, p. G10. Water Resources of a part of Owens Valley, Cal., by Chas. L. Lee, Water Supply Paper No. 294, p. 50. 1 Water Supply of San Bernardino Valley, by J. B. Lippincott, Nineteenth- Annual Rept. U. S. G. S. Part 4, p. 624. : - Some Field Experiments on Evaporation from Snow Surfaces, by F. S. Baker. Mon. Weath. Rev. July, 1917, p. 363. 138 Atmospheric Moisture and Evaporation. due to their influence in checking wind velocity, thus affecting drifting and erosion, and in shading thus diminishing the direct insolation. On the other hand these effects may be offset, particularly in the case of coniferous forests, by the lodgment of snow on the trees themselves 40 8 K I i 20 ) 1 o ( i A Ql/ A o o J o < :> ° o O j o u o o o I 1 6 f" o o & i l"o o / o o o / o * o o u O Individual Observations - Baher X ffverage of group of '/O points- o I Hrrowhead tres. C& / Ubsen /ano/73 - L/p p/r;c •on. o ♦ ,0 / 2 Evaporation from Snoyv-fncnes per Monfh. Fig. 83. — Observations of Evaporation from Snow. which increases the area exposed to evaporative action. This subject becomes of special importance in connection with the study of the rela- tion of mountain snowfall to water supply for cities, irrigation and water power. 74. Evaporation From Land. — The character and depth of the soil or other surface material, the condition of the surface, whether bare, cultivated or with vegetation, its composition and underdrain- age as well as the various factors hitherto discussed, all have import- ant influences on the amount of evaporation from the land. Evaporation From Soil 139 V. 3.6 S^ %3.e $3.0 •^ 2.8 !** ^? £ 76 %'■' \ QS %06 ^ Q4 ^ o 4.2 4.0 I 3.8 3.6 Al -D/ckenson and 7-vans 7Txp. / 835-/ 8 75 A_ A c $ W< y J1 v : 1 4 if' \ //1/c f \ ; ,-'\ t '// f -V- \ / ft, 4i • \ V JFMAMJJA 5 O N D < ^3.4 %3.2 %2.8 £ /S C * 0.6 X 0.4 ^ 0.2 O 06 04 02 4.2 4.0 3.8 3.6 3.4 3.2 30 28 26 2.4 22 20 /8 76 74 1.2 70 Q8 0.6 0.4 02 MAMJJA5 07VD °JFrtAMJJASOA/D Fig. 84. — Evaporation from Soils (see page 141). c -Re )//?< 7ms fee ' Experiments J 8 7 Hi 930 \ \ \ ^\ V \ o<" A // \\ .1 : FT I V, P- $ > . * i s ^o c /a I- v /O (5 s. je 34 32 30 23 I /a ^ A? I'" x a /5 - <5 reave -s- t>' o o ^•' ^0. , * r7r?" Tz 0, >o o A/ /?_ o 1 c o o o o o > o o ■ if 1 ' o 9 4 4 1 *- n& 1 1 6 — 2 4 6 8/0/2/4/6 /8 20 22 24 26 28 30 32 34 36 38 40 42 Annua/ /Rain fa// - Inches Fig. 85. — Relations between Rainfall and Evaporation (see page 141). Evaporation from Land. 141 The various experiments on soil evaporation made in the past are all subject to various experimental errors but these errors are much less in magnitude than the differences that will occur with various conditions of soil, so that they may all be regarded as fairly illustra- tive of the various divergences which will be found to exist in differ- ent locations often on the same drainage area. In all of these exper- iments the annual rainfall was measured and compared with the amount of water which percolates through the soil. The difference between these two quantities was estimated as soil evaporation. In some cases different soils were compared with each other and with the water evaporating from free water surfaces, and in one case also from a shaded water surface. The average results of each series of experiments are shown in Table 7. Fig. 84, page 139, shows the relative rainfall and evaporation as determined from experi- ments : (A) by Dickinson and Evans at Hertsfordshire, England ( 1835-1875) ; (B) by Charles Greaves at Lee Bridge, England (1860- l &75) '> (C) by Gilbert and Lawes at Rothamsted, England (1871- 1890) ; and (D) by the Geneva (N. Y.) Experimental Station (1883- 1887). In these diagrams should be noted the differences in evapor- ation between a free water surface, grass covered soil and sand (B), the increased evaporation from soil 60" deep as compared with soil 40" deep (C), and the difference in evaporation between grass cov- ered soil, bare soil and bare cultivated soil (D). The relations of annual rainfall to soil evaporation under various conditions are shown in Fig. 85, page 140. In each of these cases the annual rainfall is showm as abscissas and the corresponding evapora- tion by ordinates ; and if the annual evaporation were constant and approximately equal to the average, they would fall approximately on a horizontal line. These experiments show by their greater ap- proximation to the inclined lines, for each of which a mathematical expression (or formula) in terms of rainfall and evaporation can easily be derived (thus, the equation of the line A. B. (Diagram B) is E = 4 + .575 R) that in general soil evaporation increases with rainfall, which would normally be expected as the soil would as a rule be wet for a greater proportion of the time.* *It should be noted that the extension of the line shows an evaporation of 4 inches with zero rainfall which is evidently incorrect. A curved line passing through the origin of co-ordinates and approximating the line through the centers of gravity would agree better with theoretical conditions. 142 Atmospheric Moisture and Evaporation. «, K) »-« ^ 7 1 10 o3 t— t- * £o.2 p o B a* . 2 "3 .3 m ~ > IN 'S'Ots . . . > .to .' ^„-"00Oi gO MO CO CO p CJ j-^ 0. ft M d - -5 —' £ _• O ago , o l> 00 "" > "* ■> . i-O' a o a r-i & . [0 h3 a a ■c.5 ._» B O scicsoooao a) a) a) m c-, (nr^ " m m m n . a . n . i - B p m ,a ,a . .73°* .-«■ . "OOSoOOOfS j — j t . * . fit . 1 . . t . ai^ yH yH yrt fL| 'Op H OI-' flj p_ |A;| ^ fLH ^p_ ( ^ ; - ;z .^ ;z; T tU5 5) cocdo — t-ai t- i-n- "*00O CO 00 i.- ■"* CO CO CD -1-1 lOO) T-.00 CDO00 <« t- CO COCO CO O CD 00 to 00 2 10 CO O) rH Srlfl 0* QO Ol ^t 00 30 t- CO CO CO CJ a 1 cooooo iC CD ^ O tO O i- 000 - CO IC 10 10 I- o3 a CO ■* -# CO t- CO CO O! ©J CO Cn! Oi 00 05 ■* IO 8 iO cco COOJ CO Hi CO WOiCrtr-N «! M W rtW-t OT CM aa o3 o3 an o o ■tfjg coco 03 03 o o Jh-I *s CM 1^ CM tt« O! 4J-PV 4J -M -M CO CO TO CO 10 CO o3 03 U u o o ° OJCOJO W c a ^J^mC o3 03 (> a =« O O o3 03 0J 3 9^ r3o3 o o a a ^ Ha £ 'S'So o I

z 4 70 $1 f %\ $ J, 60 *,50 dO \^30 J? jT^SpilllI// \ *^s l >/ N 1 / j \ i i "Nj ! y — \\ LjA f [ \\ Rainfall Accompanying Hurricanes. 1 75 l>y Fig. 94, page 173, which show the weekly distribution of rain- fall in Wisconsin for six consecutive weeks in May and June, 1907. All such maps are but the result or summation of individual rainstorms which occur during the period considered. 91. Rainfall Accompanying West Indian Hurricanes. — In most •cases the rain accompanying the hurricanes from the West Indies falls / - ■ \ V s -—' / J / , ■■ \ \ ^S A. / \ *^i . —-^ i > Fig. 96. — Precipitation due to West Indian Hurricane of July 14 to 18, 1916 (see page 176). immediately adjoining the Coast near the point where the storm center reaches the land. Occasionally, however, the moisture is carried far inland and affects the country at some distance from the Coast. Two storms of this kind accompanied by rainfalls of considerable magnitude occurred in July, 1916. The first of these two storms entered from the Gulf of Mexico through Mississippi about July 5 and was dissipated when it encountered the southern span of the Alleghenies in South Carolina on July 13. This was followed by a record storm which 76 Precipitation. reached the coast of South Carolina on July 14, producing a heavy- rainfall near the coast on that date, and proceeding to the northwest was also dissipated against the Southern Alleghenies on July 16 with an unusually intense rainfall. The progress of the storm for the four days, July 14, 15, 16 and 17, is shown in Fig. 95, and the combined rainfall for the entire storm is indicated on the relief map shown in Fig. 96, page 175. These maps show both cyclonic and orographic rainfall, resulting from the storm. The rainfall near Altapass North Carolina for the 24 hours on July 15 and 16 amounted to 22.22 inches,. 6S°30 Fig. 97. — Rainfall on the Island of Porto Rico, resulting from the Hurri- cane of Aug. 5 to 9, 1884. being one of the heaviest rains which has ever visited the United States. The rainfall in the island of Porto* Rico accompanying the hurricane of August 5-9, 1889, is shown on Fig. 97. Here the source of mois- ture is close at hand and the consequent rainfall is much greater than would commonly be the case over continental areas. g2. Rainfall Accompanying General Cyclonic Storms. — The gen- eral distribution of rainfall accompanying the cyclonic storms for March 20 to 23, 1913, inclusive has already been shown in Fig. 31, page 70, and the distribution for the four following days of March 24 to 27th, inclusive, is shown in Fig. 134, page 249. These storms led up to the extreme flood of March, 19 13, in Indiana, Ohio, and the states farther east. Figs. 98 and 99. pages 177 and 178, show the summation of the rain Rainfall Accompanying Cyclones. 77 Hydrology — 12 78 Precipitation. Rainfall Accompanying Cyclones. 1 79 accompanying various typical cyclonic storms. 5 Fig. 98, map A, shows the path of a cyclone of January 1-16, 191 1, from Arizona on a central track with heavy precipitation on both sides of the path, showing the influence of moisture from the Great Lakes, the Atlantic and Gulf sources and the well watered interior. Map B shows the path of the cyclone of April 30-May 5, 1910, of Texas origin following a central track. The heavy precipitation is to the north of its path and is evidently influenced by moisture from the Great Lakes region. Map C shows the path of a cycline of March 22-24, 191 1, originating in Texas and following the southern track. The heavy precipitation is on the south of the path and is evidently from moisture received from the Gulf and ocean. Map D shows the path of the cyclone of April 19-28, 19 10. There are two areas of precipitation separated by a rainless area. The path passes between two areas of heavy rainfall and the precipitation is evidently derived from the Great Lakes, Atlantic, Gulf and Pacific sources of moisture. In Fig. 99 map E shows the path of the cyclones of Feb. 22-March 1, 1910. The northern cyclone caused precipitation from the Pacific northwest through the Great Lakes region. The second cyclone on the southern track caused the heavy precipitation from the Gulf up the Mississippi Valley to the Great Lakes region. Map F shows the path of the cyclone of April 16-22, 191 1, which entered the United States from Alberta and crossed on a northern course. Heavy precipitation followed on both sides of the path, evi- dently from the Great Lakes and Atlantic sources, and also to the southward, evidently from Gulf sources. Map G shows the path of the cyclone of May 23- June 3, 19 10, which path was wholly in Canada. The heavy precipitation was much broken and was apparently to the south of the path and from Pacific, Atlantic, Gulf, Great Lakes and interior sources. Map H shows a typical case of the rain accompanying a thunder- storm and included in the general rain area of the cyclone of July 23, 191 1, when the storm center was located over Iowa at 8:00 A. M. on July 23, 191 1, Washington time. 93. Thunder Storms. — Many cyclonic storms are accompanied by only slight barometric gradients and the circulation of air is so weak 5 The Cyclonic Distribution of Rainfall, W. G. Reed. U. S. Weather Re- view, Oct. 1911. 80 Precipitation. ■^ "=^\ n V)Vv 1 t yU\ n^Vo ^/lS@ % 4 IT, v. \ \/ \ K, "^ o-<> )) ) VVTg VTV - ?/ ' f ° -3*^ J- -->-^4iC--- s Ti ' 2/ 3jt1 vlr h Mi $Sf \T, ) § i 1 t Jfll O T~ft 1\° °i r lt , § s ^ ) '^1 is ^^J ^f :: \><_ 'q iz _«1 5) 1 S3 § ft 1 ir ill ° V P^il T /SQ [l A> ^ "s^ 78 7/ <~> jT 7§^/ 182 Precipitation. Jq (o§ 1 o" <5 ^T^ 7 ~) ^f -_^=>j§ , \ \ s~ith r^\ ^f^y<^) i (0\M JJ7__/N 1 C5 \j. vK u° \l l ° l r — / ° I ~~0 fyS] W — i Thunder Storms. 183 that smaller local secondary cyclones are frequently generated through local conditions. These are usually accompanied by electrical disturb- ances and heavy local rainfall and are known as thunder storms. Numerous similar local disturbances caused by intense convectional action are developed in the equatorial belt where the "afternoon thunder storm" is of almost daily occurrence. In the United States these storms are of only occasional occurrence on the Pacific Coast but increase in number toward the east, and reach Fig. 103. Jan Feb Mar Apr May June July /lug Sept Oct Nov Dec -Average Number of Thunder Storms occurring Monthly at Various Stations for the Period 1904-1913, inclusive.s a maximum in the extreme southeast. Their normal geographical and seasonal occurrence during the ten years 1904-1913 is shown by Figs. 100-102,° inclusive pages 180, 181 and 182. The normal variation in the occurrence of thunder storms, from month to month during the year at widely scattered locations is shown in Fig. 103. 94. Annual Expectancy of Storms. — The expectancy of the annual occurrence of thunder storms is shown by Fig. 104 which is based on the average for the ten year period 1904- 19 13. The approximate mean expectancy for cyclonic storms is illustrated by Fig. 105, 7 which is taken from Dunwoody's map summarizing the 6 Distribution of Thunder Storms in the United States, Wm. H. Alexander, Monthly Weather Review, July, 1915. 7 Bulletin A, U. S. Weather Bureau. 84 Precipitation. Fig. 104. — Average Annual Number of Thunder Storms in the United States, based on observations from 1904 to 1913, inclusive (see page 183). Fig. 105. — Annual Cyclonic Storm Frequency in the United States. Artifical Production of Rain. 1 85 international meteorological observations for the period 1878- 1887. Later information is contained in Supplement No. 1, U. S. Weather Review for 19 14. 95. Artificial Production of Rain. — Various men have at different times declared that they could produce rainfall, usually by one of two methods, the discharge of explosives or the liberating of gases. This belief obtained such widespread acceptance that the United States Government undertook some experimental tests in 1892. Heavy char- ges of explosives were sent up into the interior of the clouds by means of kites and balloons, and there exploded, but without effect. The results obtained by various experimenters have not shown that any rain has fallen due to the agency of man. Similarly, the shooting of vortex rings, and the ringing of bells, as is done in France at the approach of hail storms, have no noticeable effect upon either the formation or path of the storm. No one who appreciates the great atmospheric movements and dynamic changes that take place during rainstorms will believe that, by any process possible to man, any material control can be effected over such storm movements. LITERATURE CAUSES OF RAINFALL The Cause of Rain and the Structure of the Atmosphere, Franz A. Velschow. Trans. Am. Soc C, E. Vol. 23, 1890, p. 303. The Causes of Rainfall, Prof. W. M. Davis. Journal New England Water Works Association. June 1901. How Rain is Formed, H. F. Blanford. Sci. Am. Sup. May 11, 1889. Analysis of the Causes of Rainfall, G. E. Curtis. Bui. No. 7, Forestry Di- vision U. S. Dept. Agriculture, 1893, p. 187. CONDITIONS AFFECTING RAINFALL Effect of Wind Currents on Rainfall, Curtis. Eng. News, Jan. 3, 1885. Mountain and Lower Level Differences. Rep. Chf. of Engrs. U. S. Army. 1874, part II, p. 375. Irrigation and Increase of Rainfall. Eng. News, 1906, part I, p. 213. Forests and Rainfall, H. A. Hazen. Eng. News, 1898, part I, p. 5. The Relation of the Atlantic Plain to the Humidity of the Central States and Plateau Region, Science, July 18, 1913. INFLUENCE OF FORESTS Relations of Forests to Rainfall and Runoff. Eng. News, 1908, part II, p. 365. Effect of Forests on Rainfall, W. L. Moore and G. F. Swain. Eng. News, 1910, part I, p. 246 and p. 427. Effect of Forests on Snow and their ComMned Effect on Water Supply. Eng. News. 1901, part II, p. 209. 86 Precipitation. Effects of Forests on Rainfall. Rep. Ch. of Engrs. U. S. Army. Eng. News, 1875, part II, p. 172; 1879, p. 1211; 1884, p. 662. Forest Influences on Rainfall and Climate, B. E. Fernow, M. W. Harrington, Cleveland Abbe and G. E. Curtis. Bui. No. 7, Forestry Div., U. S. Dept. Agriculture, 1893. Pseudo Science in Meteorology, B. E. Fernow. A warning against conclu- sions as to effects of forests on meteorological conditions and stream flow. Science, May 8, 1896. RAIN MAKING The Facts about RainmaJcing, G. E. Curtis. Eng. Mag. July, 1892. Rainmaking, Prof. Fernando Sanford. Sci. Am. Sup. Aug. 11, 1894. Chicago, Rock Island and Pacific Railway Experiments. Eng. News, 1895, part I, p. 105. Eng. News, 1901, part I, p. 32. Dept. of Agriculture Circular Letter. Eng. News, 1894, part I, p. 318. Dis- couraging farmers in hope of rain production. Production of Rain by Concussion- Eng. News, 1891, part II, p. 34-307. Experiments in Australia. Eng. News, 1903, part II, p. 364. CHAPTER VIII RAINFALL MEASUREMENTS AND RECORDS 96. The Measurement of Precipitation, Instruments Used. — The ordinary rain gage as used by the United States Weather Bureau (Fig. 106,) consists of a galvanized iron cylindrical can, eight inches in diameter, the mouth of which is circular, beveled on the outside to Front View Vertical Section Horizontal Section, E.F I ? 3. 4 S b 7 3 9 IO II 12 13 IS 20 21 2Z23 24 Sca/e in inches Fig. 10G. — The Ordinary Form of Rain Gage form a sharp edge. This receiver is funnel-shaped ; the orifice leading from the funnel discharges into a brass cylindrical vessel, twenty inches in depth, the inside area of which is exactly one-tenth of the area of the receiver rim. The depth of rain caught in this interior tube is measured by means of a wooden scale to tenths of an inch, thus measuring the rainfall caught in the gasre to hundredths of an inch. 1 88 Rainfall Measurements and Records. When used in measuring snowfall, the funnel-shaped entrance or rim of the tube is removed and the snow is caught directly in the outer can. The snow is then melted and the equivalent depth of water measured as in the case of rainfall A more satisfactory means of obtaining the amount of precipitation occurring in the snowfall is, however, to take several samples by inverting the can of the gage over a field of snow free from drifting or other wind effects, and melting the samples so taken. Recording gages for measuring the quantity and rate of precipita- tion operate on various principles. The one perhaps in most general use in this country is the tipping-bucket gage. This gage is usually so constructed that a bucket becomes filled with i/ioo inch of rainfall, when it tips, brings another bucket into position, and records the movement upon a revolving drum. "The collector, and, in some gages, the middle section, are sep- arately detachable from the lower section of the inclosing case, in order to facilitate access to all the parts. "The top section, called the receiver or collector, is made of a sharp- edged brass rim, accurately twelve inches in diameter inside, and pro- vided with a funnel-shaped bottom and a small tube at the center so that all the water falling within the collector is conducted to a point directly over the center of the tipping-bucket bearings. The middle section is made of galvanized iron, with a hinged door, and the lower section, or reservoir, is also of galvanized iron, and pro- vided with a brass stopcock at the bottom, for emptying the gage of water. "A portion of the bucket frame and the tipping bucket is mounted on a detachable brass frame carried on brackets within the inclosing case. The brass bucket is divided by a central partition into two equal compartments. "This bucket is mounted on suitable bearings placed below the cen- ter of gravity. Two stop pins on the side of the bucket limit the move- ment of the bucket on its axis and permit it to rest in one of two posi- tions, in which either one or the other of the compartments of the bucket is presented in such a manner that it will receive and retain the water delivered through the funnel to the collector. The weight of the bucket and the position of its center of gravity have been so adjusted in relation to its supports that when one of the compartments has been charged with the quantity of water representing one one-hundredth of Measurement of Precipitation. 1 89 an inch of rain in the twelve-inch gage, the bucket tips over upon its bearings, emptying the water from the one compartment, and at the same moment presenting the other compartment to receive the incom- ing water. The water thus delivered from the buckets is retained in the reservoir section for subsequent measurement in bulk. "The automatic registration of each hundredth of an inch of rain- fall, that is, each tip of the bucket, is effected by aid of an electrical circuit closer. A short sector is attached to the tipping bucket and when the bucket is at rest in either of its limiting positions the sector stands near to, but not in contact with, a pin on an insulated contact spring. "In the act of tipping, after the bucket has moved a little, the sector makes contact with the pin, and rubs over it during the greater part of the subsequent motion. This effectually closes the electric circuit which is formed between the whole metallic framework, including the bucket, and the insulated spring. During the last portion of the tip of the bucket the sector slips off and moves a small distance away from the pin, thus opening the electric circuit, and also leaving the bucket perfectly free to tip with the next hundredth of an inch of rain." 1 ' Other recording gages operate by floats or by weighing. In the case of the float type of gage, a float rises and falls with the increase and decrease of the water level within the receptacle and by so doing traces a line upon a revolving drum. In the Marvin weighing rain gage, the necessary vessel is kept in balance as the rain descends, by a counter-weight which is automatically moved by a magnet. Each impulse which is recorded on the sheet attached to the revolving drum, corresponds to i/iooo of an inch of rainfall. 97. Exposure of Rain Gages. — The exposure of rain gages is a very important matter if accurate results are to be attained. The wind is the most serious disturbing cause, and when it blows against the gage it forms eddies near and above the mouth of the gage and frequently carries away the precipitation, especially when in the form of fine rain or snow and hence causes the gage to give erroneous re- sults. Snow is frequently blown from the gage even after it has fallen into it, and the ordinary gage is of little value for the measure- ment of snowfall. The stronger the wind the more it is apt to affect the catching of 1 Measurement of Precipitation, C. F. Marvin. Circular E. Instrument Di- vision, U S. Weather Bureau. 1 90 Rainfall Measurements and Records. precipitation, and two gages differently exposed are apt to register considerable differences even when located quite near each other. "In a high location eddies of wind produced by walls of buildings divert rain that would otherwise fall in the gage. A gage near the edge of the roof, on the windward side of a building, shows less rain- fall than one in the center of the roof. The vertical ascending cur- rent along the side of the wall extends slightly above the level of the roof, and part of the rain is carried away from the gage. In the center of a large, flat roof, at least sixty feet square, the rainfall col- lected by a gage does not differ materially from what is collected at the level of the ground. A gage on a plain with a tight board fence three feet high around it at a distance of three feet will collect six per cent more rain than without the fence. These differences are due entirely to wind currents. "The rain gage should, if possible, be located in an open space un- obstructed by trees, buildings or fences. Low bushes and fences, or walls that break the force of the wind in the vicinity of the gage are, however, beneficial, if at a distance not less than the height of the object. Gages should be exposed upon roofs of buildings only when better exposures are not available ; and, when so located, the mid- dle portion of a flat, unobstructed roof, generally gives the best re- sults." 2 98. Location of Rain Gages of the United States Weather Bureau. — The gages at the United States Weather Bureau stations in large cities are usually located on flat roofs. This altitude, together with the influence of surrounding buildings, has a considerable effect upon the air currents around the gage, and consequently the propor- tion of actual precipitation caught by the gage is more or less affected. Alfred J. Henry 3 gives the following comparisons in rain gage registers on buildings and in the open areas : St. Louis — The rain gage is located on the city post office, twenty feet from the edge of the roof and 100 feet above the street. The Forest Park rain gage is situated four miles west, in an open space seventy- five feet from any object and with its rim four feet above the ground. A comparison of the records for five years (1891-1895) shows that the post office gage records greater precipitation in the winter, while the Park gage shows the greater amount in warm weather, especially 2 Ibid. 3 Rainfall of the United States, A. J. Henry. Report of the Chief of the Weather Bureau, 1896-7. Effect of Wind. 191 in May and June. On the yearly average, the park gage records a rainfall of about two inches — or five per cent greater than the post •office gage. Philadelphia — The Weather Bureau gage is located on the post office, 1 66 feet above the street. Mr. L. M. Dey made a comparison between the post office gage and a ground gage located three miles east. An average covering six years shows that the ground gage registered three inches or eight per cent per year more than the post office gage. New York — Weather Bureau gage is situated on the roof of a building 150 feet above the street. A comparison is made with the records of the Central Park gage, which is sixty-three feet above the ground. Covering a period of twenty years, shows that the Weather Bureau gage registers 2.17 inches or about 5 per cent greater than the •Central Park gage. These variations are probably due to the effect of local air currents in carrying a greater or less amount of the falling rain out of the mouth of the gage. 99. The Effect of Wind.— The value of rainfall records for hydrological, agricultural or meteorological studies depends upon the accuracy with which they represent the actual occurrence of rainfall over the area under investigation. Any single gage can measure only the precipitation occurring within its own areas, and its application to a wider area must be on the assumption that the precipitation is uni- form over the area to which the data are applied or that the rainfall varies uniformly between gages when the data from two or more gages .are utilized. It is well understood that local topography and the position of the gage with reference to the height above the surface of the ground and with further reference to trees, buildings or other objects, together with the relative direction and amount of the wind, may produce great differences in the amount of rainfall collected by a series of gages. The difference in the amount of rainfall which will be collected by gages exposed at different heights above the surface of the ground has been conclusively shown to be due to wind currents. Jerome explained this phenomena as follows : 4 "To show clearly the nature of this effect we may imagine the stream •of air M N (Fig. 107, page 192) to be suddenly contracted at B C to 4 See Philosophical Magazine, 1861; also The Effects of Wind Currents on Rainfall. G. E. Curtis, Signal Service Notes, No. 16, 1884. 92 Rainfall Measurements and Records. half its previous thickness, so that of course, it must there commence to move with double velocity. At A D the stream dilates to its original size, and of course recovers its first velocity. The course of equidistant rain drops falling into wind under such imaginary circumstances would be represented by the oblique lines, and it is obvious that less rain would, fall in the windward part of the contracted space than elsewhere." Fig. 107. — Effect of Wind upon the Catchment of the Rain Gage (See page 191). For the same reason, with rain gages located on a roof the gages to> the leeward will catch more rain than those to the windward, and with the location of gages on a mountain top or in other positions where the direction or intensity of the wind may seriously affect the catchment of the rain, considerable difference will be found between, gages set in the same vicinity. 4 The difference in the measurement of rainfall by various gages is often marked. In the winter of 1852-3 there was established at Roth- amstead Experimental Station, in England, a rectangular rain gage 6 feet wide by 7 feet 3.12 inches in length, having an area of one-thou- sandth of an acre. 5 This large gage was established partially for the 5 Amount and Composition of Rain and Drainage Waters Collected at Roth- amstead, by Lawes, Gilbert & Warington, Jour. Royal Agric. Soc. of England. Vol. 17, 1881, p. 224. Effect of Wind. 193 accurate determination of rainfall and partially to allow the collection of the rain in sufficient quantities for chemical analysis. The surface of the gage was two feet above the level of the surrounding ground. Closely adjoining this gage and at the same elevation above the ground surface was placed an ordinary rain gage consisting of circular copper funnel 5 inches in diameter, delivering into receptacle enclosed in a metallic cylinder. Observations for 28 years showed that the small gage indicated a distinctly less average quantity of rainfall than the larger gage. The means of the 28 years readings (1853-80) of both the large and small gages are shown in Table 14. TABLE 14. Comparison of the Large and Small Rain Gages. (Means of 28 Years) Mean Monthly Rainfall D efficiency of Small Gage Large Gage Small Gage Actual Percent Inches Inches Inches January 2.500 2.263 0.327 12.6 February 1.72S 1.508 0.220 12.7 March 1.693 1.399 0.294 17.4 April 2.008 1.803 0.205 10.2 May 2.329 2.149 0.180 7.7. June 2.451 2.272 0.179 7.3 July 2.704 2.533 0.171 6.3 August 2.643 2.440 0.203 7.7 September 2.638 2.403 0.235 8.9 October 3.089 2.784 0.305 9.9 November 2.345 2.113 0.232 9.9 December 2.084 1.861 0.223 10.7 Total for Year 28.302 25.528 2.774 9.8 Some of the causes contributing to this difference were manifest, for example: a heavy snowfall was much better retained by the large gage than by the small one ; the deposits of mist, dew and frost were also dis- tinctly greater with the large gage. The effect of winds on the smaller gage was probably the main contributing factor for other differences. ioo. Records of Rainfall of the United States. — The sources of rainfall data in the United States, so far as generally available, may be found in the following publications : Abstracts of all the records of observations of rainfall which have been made from the early settlement of the country down to the close of the year 1866, so far as they could be obtained, were contained in Smithsonian Contribution to Knowledge No. 222, published in 1874, and entitled "Table and Result of the Precipitation and Snow in the United States," by C. A. Schott. Hydrology — 13 1 94 Rainfall Measurements and Records. In 1872, the United States Signal Service began the publication of the results of the observations made at various army stations by the post surgeons of the United States Army in the "Monthly Weather Review," including in this publication various reports of the State Weather Services and voluntary observers, Canadian stations, and various stations maintained by the Central Pacific Railway Company, the Hydrologic office, Navy Department, and the New York Herald Weather Service. Upon the establishment of the U. S. Department of Agriculture in 1 89 1, the Weather Bureau was organized as a branch of this service, and the Weather Review has since been published by this Bureau. In general this Review has summarized the current data received from both land stations and ocean vessels, as well as from several Euro- pean and Asiatic stations, but did not include the daily rainfall observa- tions until July, 1909, when it was enlarged to embody the daily observa- tions at each of the weather stations, including also various additional data secured by an association with various other bureaus of the govern- ment whereby the latter assisted in the collection of data not hitherto available from the various other localities. This continued until Jan- uary, 1914, when the publication of rainfall data was dropped from the Review. From the early '90's to 1909, the climate and crop service of many of the states published each month in various forms the rainfall and other climatological data for the particular state. In 1909, the state work was largely discontinued on account of the publication of this work in the Weather Review. The state climate and crop service reports were issued in small edi- tions, sometimes the early report being published only in a newspaper at the Section Center. They are not generally available, although usually complete files are found at the office of the Weather Bureau Section Center where duplicates for some special months and years may occasionally be obtained. These reports, more or less complete, can usually be found at the principal offices of the United States Weather Bureau. Since January, 1914, the Weather Bureau has published, under the head of "Climatological Data," the daily rainfall data of various sec- tions. These sections follow in general the geographic division of the states ; the exceptions are that the Maryland section includes Dela- ware and the District of Columbia, and the New England section com- prises the New England States. These reports are printed at the sev- Records in United States. 195 eral Section Centers and are generally available to those interested in the local sections. A limited edition, including all the various sections, is assembled and bound at the Washington office for Service use and exchange. The Weather Bureau has also published a summary of the monthly rainfall data for the United States in 106 sections. This summary is a combination of all the available rainfall data since 1870 when the gen- eral Meteorological Service of the United States was first established. Most of these sections are brought up to include the year 1908, while others, published later, include the year 1909. The summary is bound in two volumes, known as Bulletin W. The report of the Chief of the United States Weather Bureau, from the year 1891 to date, includes the annual and monthly rainfall rec- ords and other climatological data. 101. Dependability of Precipitation Records. — The dependability of many ancient rainfall records, taken in unknown ways and under unknown conditions, are open to serious question. From that which has been previously stated, it is obvious that many of the present rec- ords are also subject to more or less error. Subject, as they are, to considerable variations, it would seem unwise to use great refinement in the calculations of rainfall, and in recording rainfall one decimal place is probably the ultimate limit of possible accuracy. It should also be recognized that the rainfall maps, showing lines or belts of equal rain- fall, are only approximately correct, and that it would be impossible to show by such lines small differences in annual rainfall of less than two or three inches. When considering the occurrence of rainfall in particular storms, the conditions are further complicated by the fact that not all the stations re- porting furnish data taken at the same time. Most of the stations read the accumulated daily precipitation at 8 P. M., Washington time. The principal Weather Bureau Stations record the rainfall that occurs from midnight to midnight, while at a number of river stations the rainfall is recorded at 8 A. M. The consequence is that a rainstorm which occurs at essentially the same time at two different stations is frequently recorded as occurring on different days. Most of the principal Weather Bureau Stations are located in cities, and observations are made on top of high buildings where air cur- rents, frequently greatly modified and controlled by other buildings in the immediate vicinity, seriously affect the measured rainfall. It is probably true that the rainfall records from few of the principal sta- ! 96 Rainfall Measurements and Records. tions in the United States fairly represent the local rainfall within several per cent. Not only is the record of rainfall probably inac- curate, but the conditions from year to year are apt to change through changes both in the construction or arrangement of surrounding buildings and in the changes made necessary by the changes in loca- tion of the Weather Bureau offices. For example, the Chicago office of the Weather Bureau occupied the Major Block (elevation ninety- three feet) from June 8, 1873 to December 31, 1886; the Chicago Opera House building (elevation 132 feet) from Jan. 1, 1887, to Jan.. 31, 1890; the Auditorium Tower (elevation 238 feet) from Feb. 1, 1891, to June 30, 1905, and the Federal building (elevation 133 feet) from July 1, 1905, to date. The exposure of the rain gages at these various locations leads to the conclusion that the records are not strictly comparative, but are modified by the influence of the local condition. 6 It is evident that, as many rainstorms have definite limits and do not shade off gradually to nothing, as is shown by the clear lines of demarcation sometimes left in the dust by passing showers, there may be considerable legitimate difference in the readings of rain gages which are placed close together, in addition to such differences as may be due to the wind. Hellmann found that monthly totals of gages only 1,500 feet apart would differ by five per cent, while for individual storms they might differ even 100 per cent., and considerable difference in the annual rainfall must be expected in gages even five miles apart. 7 The above may account to some extent for the differ- ences noted in the gages at St. Louis, Philadelphia and New York, mentioned in Sec. 98. The matter of securing correct rainfall records has not received the attention that its importance demands, and it is to be hoped that the U. S. Weather Bureau, which is doing such valu- able service in many ways, will give more attention to this matter which is of great importance in hydrological investigations. 102. Estimating Rainfall on any Area. — From the previous dis- cussion it is evident that in estimating the amount of rain which has fallen on a given drainage area during a given period, much doubt will exist as to the accuracy of the results which may be obtained. Rainfall stations are often widely separated and undoubtedly their records do not always fairly represent the rain falling on intervening territory (see Sec. 121, page 245 and the records of Weather Bureau Stations) for e The Weather and Climate of Chicago, H. J. Cox and J. Armington Bul- letin No. 4, Geographical Society of Chicago, p. 152. 7 Descriptive Meteorology, W. L. Moore, p. 209. Estimating Rainfall. 97 J.9loLima Fig. 108.— Rainfall of March 23-27, 1913, in the Miami Valley. 1 98 Rainfall Measurements and Records. single storms or for .short periods are at the best only roughly approxi- mate as to the rain falling on the area between stations, and approxi- mate for the annual rainfalls. As the number of stations increases on and closely adjoining a drainage area, the accuracy of the average rec- ords as representing the average rainfall on the intervening area will in- crease, provided the stations are fairly well distributed. In making- such estimates the records of rainfall stations bunched on the area should be segregated and averaged and given only such weight as will represent a fairly uniform distribution of stations compared with the stations on the remaining area. The most accurate results can usually be obtained by drawing isohyetal lines on the rainfall map, determining the area of a given density of rainfall by means of a planimeter, and then calculating the total as the weighted average of areas with given densities of rainfall. For example, in the rainfall of March 23-27, 1913, on the Miami River drainage area (Fig. 108, p. 197), the average of the rainfall at all stations (omitting Lima, Salamonia and Camp Dennison) is 9.01 inches, while the weighted average based on the area between the isohyetal lines is 9.5 inches. In this case the stations are fairly well distributed. In many cases the distribution of stations would be much more unsatisfactory and the error in the estimate much greater. LITERATURE MEASUREMENTS OF PRECIPITATION Rain Gages Measurement of Precipitation, C. F. Marvin. U. S. Weather Bureau Circu- lar E, Instrument Division. The Practical Value of Self-recording Ram Gages, E. B. Weston. Engineer- ing News, 1889, Vol. 21, p. 399. Self-Registering Rain Gages and their Use for Recording Excessive Rainfalls. Eng. Rec. 1891, Vol. 23, p. 74. Self Registering Rain Gages, John E. Codman. Eng. Rec, March 14, 1890. Self Registering Rain Gages and Their Use for Recording Excessive Rain- fall, Rudolph Hering. Eng. Rec. Jan. 3, 1891. Rain Gage Used at Philadelphia for Rainfall Measurements. Eng. Rec. Nov. 5, 1892. Dalton's Rain Gage, Rev. J. C. Clutterbi;ck. Proc. Inst, of C. E., Vol. 60, 1880, p. 157. Prof D. T. Ansted. Proc. Inst. C. E., Vol. 50, 1877, p. 96. Rain Gages vs. Dickinson's Gage, S. C. Homersham. Proc. Inst. C. E., Vol. 14, 1855, p. 81. Rain Gage, C. Greaves. Proc. Inst. C. E., Vol. 18, 1859, p. 391. Observations with Staff Gages, S. C. Homersham. Proc. Inst. C. E., Vol. 7, 1848, p. 276. Literature. 1 99 Description of Rain Gage with Evapometer for Remote and Secluded Sta- tions, H. F. Blanford. Proc. Inst. C. E., Vol. 66, 1881, p. 398. Self Registering Rain Gage, A. Frank. Proc. Inst. C. E., Vol. 77, 1884, p. 414. Ferguson Automatic Rain Gage. In use at Worcester, Mass. sewage purifica- tion works. Eng. News, 1900. Part II, p. 448. Rainfall of the United States, A. J. Henry. Rept. of Chief of Weath. Bureau, 1896-7. The Amount and Composition of Rain Waters at Rothamstead, Lawes, Gilbert and Warington, Jour. Agric. Soc. of England, Vol. 17, 1881. See also Proc. Inst. C. E., Vol. 20, 1860, Vol. 45, 1876 and Vol. 105, 1891. EFFECTS OF WIND OX RAINFALL MEASUREMENT Does the Wind Cause the Diminished Amount of Rain Collected in Elevated Rain Gages? Desmond Fitzgerald. Jour. Asso. of Eng. Soc, 1884. The Effect of Wind-Currents on Rainfall, G. E. Curtis. Signal Service Notes No. 16, 1884. Determination of the True Amount of Precipitation, Cleveland Abbe. Ap- pendix I, Bulletin No. 7, Forestry Division, U. S. Dept. Agriculture, 1893. The Rain Gage and the Wind, Month. Weath. Rev., Oct. 1899, p. 464. CHAPTER IX ANNUAL RAINFALL IN THE UNITED STATES AND ITS VARIATION 103. Quantity and Distribution of Average Annual Rainfall. — The quantity of the average annual rainfall in the United States varies greatly at different points, as will be seen from Fig. 109, page 201, which shows the distribution of the average annual rainfall based on average local rainfalls to June 1, 1916. From this map it will be noted that "from the great plains westward the lines of equal rainfall are, approximately, north and south. In the Southern States, east of Texas, they are approximately parallel to the Gulf coast. In the East- ern States they are approximately parallel to the Atlantic coast. In the Lake region, while they approach parallelism to the parallels of latitude, yet there are some variations, evidently due to the effects of these great bodies of fresh water and their temperature at different seasons of the year. In the vicinity of Cape Hatteras and on the Peninsula of Florida, other influences come into play, modifying the direction of the lines of equal rainfall. Cape Hatteras is the point of highest rainfall along the Atlantic coast, due, undoubtedly, to the sea- sonal winds which pass at sea and reach, more or less, this prominent point. On the Peninsula of Florida we approach the tropical region and approximate the laws of tropical rainfall. East of the ninety-fifth meridian the rainfall decreases as the latitude increases. West of that in general the lines run north and south." x It may be observed that the rainfall apparently decreases with in- crease in elevation : This is very noticeable in passing along, for in- stance, the parallel of latitude 40 . The annual rainfall on the coast of New Jersey ranges from 40 to 50 inches. As we pass westward we come to the area where the rainfall is about 40 inches. This rain- fall continues along the parallel until the vicinity of the Mississippi River is reached, when it decreases with the comparatively rapid ascent of the slope to the great plains. By the time Kansas is reached the annual rainfall has fallen to 30 inches ; in western Kansas it is only 20 inches, and in passing the boundary of western Kansas we pass the annual rainfall line of 15 inches. 1 Bulletin C, Weather Bureau, page 13. Quantity and Distribution. 20 202 Annual Rainfall in the United States. These conditions of rainfall are, however, undoubtedly due to dis- tance from sources of vapor origin instead of to altitude, which, as shown in another place, with other things being equal, increases the rainfall rather than diminishes it. In general therefore, the distribution of the mean anuual rainfall is explainable on the basis of the factors already discussed. Among the mountains, on the Pacific Coast and in the great interior basin the phenomena of precipitation are more complex and the reasons for differ- ences in distribution not so evident, on account of topographical irregu- larities. Even in portions of the country where the topographical relief is ap- parently not sufficient to modify the quantity of rainfall, considerable differences sometimes occur within short distances for which there seems no adequate explanation. For example, Mather and Meadow Val- ley, Wisconsin, are about 6.5 miles apart but the rainfall of Mather ex- ceeds that at Meadow Valley by about 4 inches per year, which is fairly uniform for the six years of parallel records : Year 1912 1913 1914 1915 1916 1917 Mean Mather 33.45 37.43 32.38 31.51 32.39 30.64 32.96 Meadow Valley 30.27 30.79 27.77 31.49 27.46 25.59 28.89 Difference 3.18 6.64 4.61 .02 4.93 5.05 4.07 Appleton and Menasha, Wisconsin, are located about 7 miles apart but there is a mean difference in the annual rainfall at these two stations of about 3.4 inches, the Appleton rainfall averaging higher. Here, how- ever, the differences are not constant as will be noted from the parallel records for the last eight years : Year 1910 1911 1912 1913 1914 1915 1916 1917 Mean Appleton 24.43 36.65 30.54 37.08 35.82 28.97 33.95 28.00 31.93 Menasha 23.45 32.30 31.55 29.66 30.29 29.11 28.74 25.09 21.57 Difference 98 4.35 —1.01 7.42 5.53 —.14 5.21 2.91 3.36 It is readily understood that extreme storms will frequently give rise to great differences in rainfall at stations closely adjoining, but fortuit- ous circumstances will seldom tend toward one direction for any con- siderable term of years, and when such tendency is displayed it would seem to indicate some constant influence which affects the phenomena in the direction noted. 104. Variation in Annual Precipitation. — While the causes that produce the normal local rainfall are difficult to determine, the causes which produce the variations that occur in the total annual precipita- tion and in its distribution are still more difficult to trace. The in- Variation in Annual Precipitation. 203 vestigator must confine himself largely to a study of the actual varia- tion and the actual distribution in endeavoring to determine their lim- its and the effects due to them. The map of average annual rainfall is of value for only a general view of the subject. Even the study of the general rainfall map from year to year gives only limited informa- tion (see Figs, no and in, page 204) ; although the variations in such maps begin to show the large departures from average conditions that occur locally. The average or mean conditions of precipitation are of only general importance. The extreme conditions are those most directly modifying runoff and which seriously affect hydraulic problems. A water supply, for whatever purpose, should be constant in quantity or vary only as the demand for water varies , otherwise continuous service will be interrupted or must depend on other pro- visions ; hence the occurrence of minimum conditions will largely modify the nature and extent of works intended to conserve and equalize such supplies. The maximum precipitation resulting in extreme flood flows must, on the other hand, modify works intended for escapement and flood protection. The two maps of annual rainfall show a considerable variation in the rainfall for the years 1906 and 1904. They show, however, a general similarity in distribution even while great local differences are discernable. As a general rule it is found that great variations in rainfall are more or less local in character, and while it may be very dry in one part of the United States, it is apt to be unusually wet in some other portions. In general, wet and dry periods may occur in areas of considerable magnitude, but the great differences are more readily discernable when smaller areas are compared. 105. Variation in Annual Rainfall in Limited Areas. — For special purposes, a detail study of the local variations from the average con- ditions is necessary. Great variations take place in the annual rain- fall of every locality. Sometimes the annual rainfall will be consider- ably below the average for a series of years, and then for a number of years the average may be considerably exceeded. No general law seems to hold, however, in regard to this distribution and the variation seems to occur either without law or by reason of laws so complicated as to defy determination. The variations in the distribution of the annual rainfall in the State of Wisconsin for 24 years are shown by Figs. 112 and 113, pages 205 and 206. From these maps it can clearly be seen how greatly the distribution of rainfall throughout the 204 Annual Rainfall in the United States. Fig. 110.— Annual Rainfall 1906. Fig. 111.— Annual Rainfall 1904. state differs in different years from the average annual rainfall as shown by Fig. 114. Even in the State of Wisconsin there are few, if any, years when the rainfall in the entire state is uniformly very high or very Variation in Annual Precipitation. 205 /go/ _^jjjiBi^ *§ ^>v =1 '•y /896 /899 /90P /897 /900 /903 /904. /905 /906 D Under /5 [TTTTT1 /5 /o <^?0 10 30, zo 10 o 30 ZO 10 Set// /.aAe C//(/, (//a/?. .ID: -_D I »_n_. 1 1 1 1 1 1 1 1 1 1 n n 1 1 1 n i n 1 1 h 1 1 1 m i a n i n i n n rn rrm n i n h n ). Sa/7 /~ra/7c/sco Co/. nfl n.^_nJL _n_Jl_ fin n ■nniirmnrniiiimnrrniinnniiirmHrrmiimimni'i So/7 D/ego, Co/ IttwJ 1 iiinmnmiiniiiiiiii ■ l UffuifhlHffiil i 5 an/a r~e, /V Mex Fig. 115. — Variation in Annual Rainfall at Various Stations (see page 207). Hydrology — 14 210 Annual Rainfall in the United States. ■60 .50 -40 .30 .20 JO -r„— nH|U| Gfl~ "§¥§"# — rffcta& 4 B..--»- n n. II 1 1 II III i fin nnrnnn nn imm illy/^-:;^- '■■■■'■■' i 1 .: n:i -> -•;:;■: .- ■■■■ ; ii i it ;::w- ]■:■:■'. .^' |. ■ ■ : ". ii i Boston, Mass. -Qn._Jl_n-__.na LI II III ran iiii.niTniiiimii.nnim in ftti Defro/f, fyf/c/7. -_—____§— -rtfttiiff"t-Ui-'-tB-ti-i~l~iii-iii-y ■in 1 1 1 1 nil i nil i inn n 1 1 1 1 1 1 n i Leaver? wort/?. /fa/7. 20 JO .0 60 50 40 30 20 JO <0 Porf/and, Ore. Fig. 116. — Variation in Annual Rainfall at Various Stations (see page 207). Denver, Co/o. T A i n n ___ L - nlln tL _Q -O b __. --_-_.-__-* \ iin ■ mi nninn pirn 1 III 11 111 1 Mil 1 11 1 1111 11 llll 11111 1 II liSiill I m llll III MINIM Illlllllll Illlllllll III Variation in Annual Rainfall. 211 r C'V j_j 7 \ , . \ 4 / _ A r\ 1 \\n \ J ^ * \ / I^i^^v _ / \ ^" ^y \ \ /' \ "I 4- ' /M 11 r T\ ^ j / \ j t ' . M \ Lk f ii" i - v ' n\ / ^ > SOU7-/7 'EASTERN astH'' £:a/g/la/vo -rf / \ 5 /I V / V / Lrf Mm ' 1 L/j rrf 1 /r T / * i_/5 it T L ti-4— ^ T J \ ±]_A _M ' L A £S ± ... ..._, TTT-it ■» L-'f \ 1 \ '\ X ? x 1 / 1 M / \ ± /_.\____±i± 1 1 III 1 \W\l\ K i J W \ 1 L., [..J... -Jit / I / r- -' \ f s f w___ 4 fit ill w \\\n\ \ 1 s i y \-.ii J. fa 1 /fH 1 \ f ± A ].__ tf± II jf \ /I 1 1 1 1 1 £//=>«£-/? otf/O 'ALL£:y \ ' i ..... ..4.4111 it \.) ._j_ j_ _ — _^ _. _ i-L._ ± \ t±T jr n / \ ..:i±T]t'3r 1 / 1 r _. T / 3 _± , / \ 1 . ,\ L f\ / it V III'JT 1 ,1 V A f \ 1: ^ +1T+ S _ J] \\\\\\ \ ' '- ' / *' T \\{\\\ ' ; f \ /^i i W/5COA/5//V mT /' ^ V/ \ f\A j *L 7" ' s- ^ > ! ' T 5 r t jr v/ ^^r j >_r v-*, , j M/p£?L£: M/SS/S S//=>P>/ VALLEY 1 V \ ' Q "T\ , tT \ / \ t " _ . :::::::::: t r t rv / r :t 2_2. ,__! f * Ji-W JOAQU//V.. V4LL£ Y PsU./F-Ofr/V/A \ 1 | j A ' \ / — :::::::::::::i::::2:::J:/± _:: / \ / A-T'vr- Jr . t,__ /_ t _ 1 f / l' Jxu v-L-L' 1 ±±LJ i _/' v b t± I±T"± ±:^ \i \- ""if ilJTT - ^j^J____L _+__^ i+ f ""t \ . z.hi ± Fig. 117. — Rainfall, Progressive Means (see page 208). in the progressive mean of over ten inches. In Wisconsin, from the year 1840 to 1881, an increase of 13.5 inches in the progressive mean is shown, while the years 1881 to 1902 show a decrease of 12 inches. It is evident therefore, that to demonstrate either an actual increase or decrease in the mean annual rainfall, records are required for a much longer period than is available in the United States or elsewhere. The long periods during which the progressive mean is sometimes below or above the mean for the period should also be noted. For 2 1 2 Annual Rainfall in the United States. example, in New England the progressive mean was below the mean for the period for twenty-six years from 1833 to 1859, and above for the twenty-three years from 1859 to 1882. In Wisconsin, the pro- gressive mean was above the period mean for twenty years from 1867 to 1887, and below the mean for the ten years from 1892 to 1902. Usually, however, the departure in one direction is for more limited periods, as an examination of the various curves will show. The error* that must therefore occur in drawing any conclusions from a short series of observations is manifest. These diagrams of mean rainfall, together with much longer rec- ords in foreign countries, lead to the conclusion that while considerable variations must be expected, yet such variations are within certain limits, and that a record of forty years will give a mean from which the mean of any other similar period will hardly depart more than a few percent. While geological research shows conclusively that great changes in climatic conditions have taken place in times past, and un- doubtedly will take place in the future, yet these changes have occu- pied thousands of years ; and while the records of centuries may show radical variations in rainfall conditions, yet so far as the life of man is concerned, the variations in annual rainfall are due essentially to the great swing in the pendulum of conditions, the cause of which we know not, but which we can confidently expect when extremes are reached to gradually revert to the opposite conditions. In other words, it is clearly evident that so far as the life of man is concerned, the rainfall conditions remain essentially unchanged except for the varia- tions from average conditions, the extent of which can be fairly well established by an examination of available records. In the changes of ages, the character of which we have not sufficient data to recog- nize, mankind has no practical interest. 107. Detail Study of Local Variation in Annual Precipitation. — Having briefly discussed the general variations in annual rainfall, a better idea of the subject may be secured by examining the rainfall of a smaller territory in greater detail, and for this purpose the State of Wisconsin has been selected. Fig. 118, page 213, shows both the actual departure from the mean for the recorded period or rainfall observations at various stations in or near Wisconsin, and the pro- gressive mean during such period. It will be here noted that the variations in the annual rainfall, even in the limited area considered, are not synchronous. The period of maximum rainfall at Milwaukee was from 1874 to 1879, while at Madison it was from 1878 to il Detail Study of Local Variation. 213 While in some cases a certain similarity exists in the progressive mean, in no two cases are the variations uniformly parallel. The records of precipitation show not only a considerable variation in the annual amount, but also show that the annual distribution throughout the mmi.3 nuun.ui.H uiu ii.ii.Mi uMiii ^ £"\ ■ - / z n i ~ ;r ~~ j V " . ■ e „!*„ mxuAiiX t^> _6>i-r ^ ji^ii ,." .-, <» /~VT T r' T t T~r 11 Y Mlwx ur.t: t ' """ i: T ° 6^^ * /^v ~"~ T T T-- 7 x \* M'AN ^A4/J>»i-5/,S /^-^"IX . >^N *y ^ " MAD/SON | ' /, * x \> 1 Jl l^^c\ •]r::"::::::]r-]r:]^^":lr:::::::; 6 i i if^vl 'i '■" . ,^\ ?i A >»-L ^ — ^ *\j, d> ,. a_jl «. J PATA//J/E:' DU CH/EN " \.; '■• 3 LA CROSSf. \ /' » \ " / " ;t:: "> 4- r - - J"S 'L- s " ^v ^j^°° » *»**-»»- am/v/7-£wc>c J, ^rf ^"-' if^LjI T.^f^^bJ^ I_ 5 ^ ■= ir i " "T -3 ^' ~i~ , 7 = V ,: ,f " GREEN' BAY ' £^~~- U 'Si, x ^vJ^. * + >v " i: :~"it _> ' * .«' / V o :c » ■' . T^" \ ° „ 6 O i V i _ii£::_:__- * * ^f30 *20 P O ■10 -20 40 -60 J SI L 1 a A3i ?27 |S *i i \ */S ■-. i i ij . . £££2 +475 \ \ '275 >22£ H7S Datum Line of Mean Pamfc 1 ! J -2 IS -226 -178 -822 -475 — 7 i \ -IS i 25 -31 - 40 * /£ 20 years 35 Fig. 120. — Average Deviation from Mean Annual Rainfall, by Binnie (see page 215). mean annual rainfall than will probably be found in many extreme cases. no. Expectancy of Future Rainfall Occurrences. — The future must be judged by the past, and the study of rainfall variations is gen- erally for the purpose of judging what extremes must be expected in the future. The occasional occurrence of more extreme conditions 5 10 15 20 Max. Dev. above Mean. . 32.1 19.3 11.9 11.6 Max. Dev. below Mean.. 30.4 18.9 15.5 12.9 Ave. Dev. above Mean. . 17.61 9.67 5.59 4.43 Ave. Dev. below Mean. . 16.09 9.62 6.57 5.11 Min. Dev. above Mean. . 6.8 1.0 1.1 0.0 Min. Dev. below Mean . . 7.8 4.7 0.8 0.0 16.85 9.64 6.08 4.77 Extn erne Dev. from Ave. 16.15 9.66 9.42 8.13 Extreme Variations. 2 1 7 TABLE 15. Deviations from the Mean Value of the Annual Rainfall During the Period of Record — Expressed in Percentages of the Mean Local Rainfall as De- termined by A. R. Binnie. From 4~ Records of from 50 to 97 Years 25 30 35 40 45 50 9.9 9.2 7.1 5.7 4.8 3.8 10.7 9.7 7.7 5.1 2.9 4.1 3.43 2.91 2.41 3.23 2.60 2.72 3.78 3.16 2.20 2.21 1.34 2.33 0.0 0.0 0.0 0.3 0.7 1.5 0.0 0.0 0.0 0.0 0.1 0.0 3.60 3.02 2.30 2.77 1.96 2.52 7.10 6.67 5.40 3.28 2.83 1.58 From 26 Records of from 50 to 60 Years Max. Dev. above Mean 23.2 Max. Dev. below Mean 29.6 Ave. Dev. above Mean 15.35 Ave. Dev. below Mean 14.51 Min. Dev. above Mean 6.8 Min. Dev. below Mean 7.8 Average Deviation 14.93 Extreme Dev. from Ave 14.67 than have hitherto been experienced is a warning that as time passes even still greater variations must be expected. A graphical analysis of the annual rainfall at Madison, Wisconsin (Table 20, p. 238), is shown in Fig. 121. In this figure the two limiting horizontal lines show the extreme maximum and minimum annual rain- falls in the 48 years of record, namely 52.93 and 13.49 inches. The next highest and lowest annual rainfalls, namely 49.19 and 20.17 inches, are platted on the 24-year ordinate point as representing the next in magnitude of the two highest or lowest occurrences in 48 years, and therefore, the limit above and below which two annual rainfalls must be expected within 24 years. In the same manner the least and greatest of the three highest and lowest rainfalls that have occurred in the 48 years of experience are platted on the 16-year ordinate, and so on throughout the table, the points platted furnishing a guide for the establishment of the lines marked "lower limit of maximum experience," and "upper limit of minimum experience." The shaded area between these lines and 10 15 20 25 30 35 14.9 9.2 5.1 7.3 5.2 4.5 16.1 12.5 9.2 9.0 6.9 4.7 8.08 3.87 2.47 2.50 2.17 1.73 8.37 5.64 4.08 2.94 2.37 1.86 1.0 0.0 0.0 0.0 0.0 0.0 4.7 0.8 0.0 0.0 0.0 0.0 8.22 4.75 3.24 2.77 2.26 1.78 7.88 7.75 5.95 6.25 4.64 2.72 218 Annual Rainfall in the United States. the horizontal lines first mentioned sIioavs the limiting field of the ex- perience in Madison. The "mean curve of maximum experience" and the "mean curve of minimum experience" are the curves drawn through the means of the one, two, three, four, etc., highest and lowest records respectively, in accordance with the data shown in Table 16. 84-/2 frequency 2 /6 20 24 28 32 Years of Exper/'ence Pig. 121. — Graphical Analysis of Rainfall Experience at Madison, Wis. The limiting curves above noted are platted from Columns 2 and 3 of this Table, and the mean curves are platted from Columns 5 and 6. This diagram shows that based on past experience a maximum rain- fall of 52.93 inches should be expected in 48 years ; that in 24 years two maximum rainfalls must be expected of 49.19 inches or more, averaging 51.06 inches, etc. The prolongation of this curve which is expanding from the average in both directions, would indicate that as time passes greater and lesser annual rainfalls must be expected and an estimate of such intensity may Expectancy of Rainfall Occurrences. 219 be made by prolonging the curve. Such a use of the data is, however,, extremely dangerous as it is evident that with any gradual increase, if the time is sufficiently prolonged, a minimum of zero would be reached on one hand and an infinite rainfall on the other, both of which are ab- surd. Judgment would indicate that such curves must ultimately be- come parallel with the base when the most extreme conditions are reached, but what those extreme conditions are, is indeterminate. TABLE 16. Experience Table of Annual Rainfalls at Madison, Wis. Rainfalls in Number Mean Order Order of of Annual of Magnitude Annual Rainfall Magnitude Inches Rainfalls Inches Maximum Minimum Averaged Maximum Minimum. 1 52.93 13.47 1 52.93 13.49 2 49.19 20.17 2 51.06 16.83 3 46.72 20.24 3 49.61 17.97 4 42.89 22.44 4 47.93 19.90 6 40.58 22.80 6 45.57 20.29 8 38.89 24.24 8 43.98 21.13 12 36.98 25.67 12 41.81 22.43 16 35.21 28.13 16 40.28 23.70 24 31.25 31.25 24 37.60 25.66 Mean Annual Rainfall, 31.63. Fig. 121 also contains a maximum and minimum probability curve which is discussed in Section in. Such curves, while instructive, can not safely be used for estimating future occurrences except within wide limits. This is well shown by comparing the three experience curves of the annual rainfall at Boston, Massachusetts, shown in Fig. 122, p. 220. In this case, 100 years of observation are available and curves have been drawn for the 50 years from 1818 to 1867 and from 1868 to 1917, both inclusive, as well as for the entire 100 year period. From Fig. 122 it will be seen that during the first 50 years both the maximum and the minimum rainfalls for the entire 100 years were ex- perienced, and the occurrence of that period could not be inferred from the experience curve for the last 50-year period. The curve for the last 50 years if taken by itself would indicate that the minimum rainfall had been reached in that period, but the curve of the first 50 years shows that such was not the case and that even a lower rainfall must be expected. in. Rainfall Data and the Law of Probabilities. — Rainfall and other meteorological and hydrological data can be studied to advantage on the basis of the Laws of Probabilities. The method has been 220 Annual Rainfall in the United States. 25 O /O 20 30 40 SO SO 70 SO 90 /OO Years Pig. 122. — Graphical Analysis of Rainfall Experience at Boston, Mass. utilized in certain extended investigations by Mr. Allen Hazen, Mr. Thorndike Saville and others, and the methods are described in some detail in the references given. From Saville's paper, or from any work on Least Squares, it appears that* if Z = most probable value of a term in a series of observations or the mean of such observation, n = number of observations. M = any observation. v = variation of a single observation from the mean, r = probable variation of a single observation. R = probable variation of the mean. 2 = summation; then 2M Z = = mean n ■ = 0.6745 J Zy ~ — * n — 1 probable variation of any single observation Law of Probabilities. 221 R : — — == 0.6745,./ __ = probable variation of the mean Vn V n (n — 1) / SV2 _ V n-1 r n — 1 standard variation coefficient of variation. SM In Table ly the annual rainfalls of Madison for 48 years of record are shown in the order of their magnitude. The difference (v) and to 20 30 4Q 50 6Q 7Q 8Q 90 99 933 9999 \50 X - ■** < .^40 x \30 .Of ./ / IO BO 30 40 50 40 30 20 10 1 I Ol Fercenftatje of Years Fig. 123.— Probabilities of Annual Rainfall at Maidson, Wis. (Probability scale) ' (see page 197). the square of the difference (v 2 ) and the percentage of the time which the equivalent rainfall is below the amount given in the first column, are also given. From this table a probability curve is platted on the Hazen probability paper (Fig. 123). Each point in the order of its magnitude is platted in the center of a strip of width (in per cent.) proportional to the ratio of 100% to the full 100 number of terms used, i. e. ; in this case each strip will occupy ■ 222 Annual Rainfall in the United States. or 2.08%, and the first and last terms will be at absissa 1.04%, the dis- tance between points being 2.08% in each case. (Fig. 123.) If the data corresponds essentially with the normal law of error, the platted points will lie approximately in a straight line. In this case the points fall on a curve which departs somewhat from the straight normal line of errors and is indicated by the curve which very closely approxi- mates the rainfall observation at Madison. From these lines the fre- quency of the occurrence of any given amount of annual rainfall at Madison can be determined from the principle that the frequency or number of years during which a given rainfall will occur once is equal to the ratio of unity to the percentage of time in which such occurrence has taken place. The relations for Madison, as determined from this curve, are shown in Table 18. TABLE 17. Yearly Variations Variations Per cent. Rainfall from the Squared of total inches mean Time in order Cumulative of magnitude Total 13.49 18.14 329.07 1.04 20.17 11.47 131.56 3.12 20.24 11.39 129.73 5.21 22.44 9.19 84.46 7.29 22.58 9.05 81.90 9.37 22.80 8.83 77.96 11.46 23.06 8.57 73.45 13.54 24.24 7.39 54.61 15.62 24.37 7.26 52.71 17.71 24.59 7.04 49.56 19.79 25.49 6.14 * 37.70 21.87 25.67 5.96 35.52 23.96 26.81 4.82 23.23 26.04 27.49 4.14 17.14 28.12 27.67 3.96 15.68 30.21 28.13 3.50 12.25 32.29 28.17 3.46 11.97 34.37 28.78 2.85 8.12 36.46 28.78 2.85 8.12 38.54 29.05 2.58 6.66 40.62 29.45 2.18 4.75 42.71 30.29 1.34 1.80 44.79 30.83 0.80 0.64 46.87 31.25 0.38 0.14 48.96 "31.25 0.38 0.14 51.04 Law of Probabilities. 223 TABLE 17 — Continued. Yearly Variations Variations Per cent. Rainfall from the Squared of total inches mean Time in order Cumulative •of magnitude Total 31.35 0.28 0.08 53.12 31.46 0.17 0.03 55.21 31.91 0.28 0.08 57.29 32.32 0.69 0.48 59.37 32.38 0.75 0.56 61.46 32.72 1.09 1.19 63.54 34.40 2.77 7.67 65.62 35.21 3.58 12.82 67.71 35.33 3.70 13.69 69.79 36.04 4.41 19.45 71.87 36.15 4.52 20.43 73.96 36.98 5.35 28.62 76.04 37.10 5.47 29.92 78.12 37.53 5.90 34.81 80.21 38.23 6.60 43.56 82.29 38.89 7.26 52.71 84.37 39.54 7.91 62.56 86.46 40.58 8.95 80.10 88.54 41.13 9.50 90.25 90.62 42.89 11.26 126.79 92.71 46.72 15.09 227.70 94.79 49.19 17.56 308.36 96.87 52.93 21.30 453.70 98.96 Total 1,518.07 Mean 31.63 Median 31.25 2,864.43 Most probable value of annual rainfall 1518.07 48 31.63' Standard variation V 2864.43 (48 — 1) 7.807 •Coef. of variation = = 0.2468. 31.63 Probable error of a single observation = 0.6745. 7.807 = 5.266. 5.266 Probable error of the mean = 0.760. V48 100 P*er cent, of total time represented by each observation 2.0833. 48 224 Annual Rainfall in the United States. TABLE 18. Probabilities of Rainfall at Madison, Wisconsin. A.mount of Rainfall Relative Time Equivalent Time Frequency in inches of Occurrence in year Once in 26— or 36 + 25 11.8 4 years 24— or 40 + 15 7.2 6.7 23— or 42 + 10 4.8 10. 21— or 46+ 5 2.4 20. 18— or 52 + 2 0.96 50. 17.5— or 53.5+ 1 0.48 100. To determine the limiting rainfalls for a given period the correspond- ing ordinates of the percentage of years is found from the equation 100 Percentage of years = length of period -rt. r n ■ 1 , 10 ° thus, tor a five-year period the percentage of years is = 20 and 5 the ordinates to the curve at the percentage 20 are 37.5 and 25, and these figures mean that in a five-year period we should expect on an average one rainfall of 37.5 inches or more and one annual rainfall of 25 inches or less. It should be noted that the conclusions shown in Table 18 and platted, in Fig. 121, which are based on the data of Table 17 and Fig. 123, when near the mean are well established and may be considered as fairly safe and conservative, and that as the departures from the mean increase the data become more limited and the conclusions are subject to greater error. Even the frequency of once in 20 years for rainfalls of 21 inches or less and 46 inches or more will likely be found in error where the data for 100 years or more are available for study, and the frequency for one rainfall of 18 inches or less and of 53 inches or more once in 100 years is entirely unwarranted because the period is beyond experience. Such an estimate is the best that can be made with the data at hand, but should not be taken as a dependable prediction. It should be noted, however, that this method of investigation shows the extraordinary character of the minimum rainfall record and also indicates the fact that the three highest rainfalls are somewhat incon- sistent with the balance of the record. It should also be noted that a calculation of the probable extreme rainfall of once in 100 years by this method is more conservative than if based on the extension of the limiting curves of the actual experience platted in Fig. 122. This re- sults from the eliminating of inconsistencies by this latter method. Law of Probabilities. 225 If we calculate the frequency of the minimum rainfall of 13.39 i ncnes from the curve in Fig. 123, the frequency indicated would be once in 4,000 years. This must be regarded as an absurd deduction for this rainfall had already occurred in 48 years' record and it is possible that other years in the next 100 may fall short of this amount, although such an event seems improbable from the data available. This method cannot safely be used to project estimates far into the future beyond the limits of experience. Fig. 124. — Hazen's Map of Rainfall Coefficients. 112. Application of Probability Calculations. — Mr. Allen Hazen prepared a map of the United States 4 (Fig. 124) on which he has shown the relative variation in the quantity of annual rainfall in various parts of the country by means of the coefficient of variation as expressed above. Mr. Hazen says : "For the eastern part of the United States the records used are suffi- cient to show the normal conditions with a fair degree of accuracy. In the west the relative variations are greater, the records are shorter and the stations often farther apart and the results thus less reliable. "The map is to be regarded as a first rough approximation. It serves to give a fairly accurate idea of the general conditions of varia- tion in annual rainfall in the United States, but in detail it must be 4 Engineering News, Jan. 6, 1916- Hydeology— 15 -Allen Hazen. 226 Annual Rainfall in the United States. expected that more ample data, or even more complete use of existing data by extending the studies to cover everything available, would re- sult in changes in the positions of the lines. Such changes are most likely near mountains and in about that third of the country nearest the Pacific Coast. "The coefficient of variation is lowest on the Atlantic Coast. That means that one can count on getting more nearly the normal rainfall each year; and on the Atlantic Coast the coefficient does not range through wide limits. If one's experience were limited to this part of the country, he might almost neglect the range and assume that there was everywhere the same chance of a very dry year, such, for example, as is represented by a rainfall of only sixty per cent of the normal. This is in general the conclusions reached by Binnie for the data studied by him. It does not hold, however, for the whole United States. As one goes west, the coefficient of variation in annual rain- fall increases ; that is to say, the chance of a very dry or a very wet year (relatively) is increased. "In New York the coefficient of variation is 0.15; at San Francisco it is 0.30. This means that on an average the relative variations in annual rainfall at San Francisco are twice as great as at New York. A year forty per cent short of the normal rainfall comes as often at San Francisco as one twenty per cent short of the normal comes in New York. "By following this method of investigation it will not be hard to find quite definitely just how often, on an average, a year of any as- sumed relative wetness or dryness will come, and also to find what the chances are of years of any degree of dryness coming within a given period. "Other things being equal, the variations to be expected in any pe- riod at different localities will always be in direct proportion to the coefficients of variations in the respective places." LITERATURE GENERAL SUBJECT OF RAINFALL U. S. Weather Bureau. Annual Peports and Monthly Climatological Data, Monthly Weather Reviews. Meteor ologische Zeitschrift. Zeitschrift cles Oesterreichischen Gesellschaft fur Meterologie. Symon's Meteorological Magazine. Annucine de la Soeiete Meteorologique de France, Paris. The Royal Meteorological Society of Great Britain. Quarterly Journal. Literature. 227 Laws of Rainfall and Its Utilization, Thomas Hawksley. Proc. Inst. C. E., Vol. 31, pp. 53-59. 1871. Tables of Mean Annual Rainfall in Various Parts of the World, Alex R. Bin- nie. Proc. Inst. C. E., Vol. 39, pp. 27-31. 1874. Tables and Results of the Precipitation of Rain and Snow in the U. S., C. A Schott. Smithsonian Contribution to Knowledge, No. 222. Charts and Tables Showing Geographical Distribution of Rainfall in the U. S. U. S. Signal Service Professional Paper No. 9. 1883. Rainfall Observations at Philadelphia. Reports Phila. Water Bureau, 1890- 92. Eng. Record, 1891, p. 246. 1892, p. 360. Mean or Average Rainfall and the Fluctuations to which It is Subject, Alex. R. Binnie. Proc. Inst. C. E., Vol. 119 (1892), pp. 172-189. Rainfall and Snow of the United States, M. W. Harrington. Bulletin C, U. S. Weather Bureau, 1894. Rainfall of the United States, A. J. Henry. Bulletin D, U. S. Weather Bu- reau, 1897. Variation in Annual Rainfall, Allen Hazen. Eng. News, Vol. 75, 1916, p. 4. Rainfall Data Interpreted by Laws of Probability, Thorndike Saville. Eng. News, Vol. 76, 1916, p. 1208. The Probable Growing Season, W. G. Reed. Month. Weath. Rev., Sept., 1916. Elementary Notes on Least Squares, the Theory of Statistics and Correlation for Meteorology and Agriculture, C. P. Marvin. Month. Weath. Rev., Oct., 1916, p. 551. This article also contains a bibliography on the subject of probabilities and statistical methods. The Average Interval Curve and its Application to Meteorological Phenomena, W. J. Spillman, H. R. Tolley and W. G. Reed. Mon. Weath. Rev., Apr., 1916, p. 197. Frequency Curves of Climatic Phenomena, H. R. Tolley. Mon. Weath. Rev., Nov., 1916, p. 635. Predicting Minimum Temperatures, J. W. Smith. Mon. Weath. Rev., Aug., 1917, p. 402. CHAPTER X SEASONAL RAINFALL IN THE UNITED STATES AND ITS VARIATION 113. Seasonal Variation in Rainfall. — Climatic conditions are, in a general way, fairly consistent, and as the seasons change, conditions obtain favorable or unfavorable for precipitation. The maximum and minimum monthly rainfall occurs, therefore, at every locality at fairly Fig. 125. — Seasonal Rainfall of the United States. definite periods. Rainfalls vary considerably from year to year, but have, nevertheless, the same general character. The mean seasonal distribution of rainfall in the United States and the percentage of the annual precipitation that commonly falls during the wet season of the year, are shown in Fig. 125, upon which the radically different occur- rence of rainfall in various localities is indicated. Fig. 126 shows the percentage of the mean annual rainfall that com- monly occurs from April 1 to September 30. It may be noted that the high percentage of the rather low rainfall on the Great Plains occurring during the growing season is a condition favorable for agriculture. Seasonal Variations. 229 Fig. 127, page 230, shows typical fluctuations of the rainfall for vari- ous months in the year at a number of places throughout the United States ; and more extended types of the monthly distribution of pre- cipitation in the United States are shown in Fig. 128, page 231. In Fig. 128 the monthly averages of a number of stations have been reduced to percentages of the average annual fall. The character of the monthly distribution varies widely at different locations, but will be seen Fig. 126. — Percentage of Mean Annual Rainfall Occurring from April 1 September 30 (see page 228).* to to have a similar character wherever similar conditions prevail. Thus the New England States present a similarity in the distribution of the monthly rainfall. A similarity in the monthly distribution is also found throughout the lake region and the Ohio Valley. The monthly distribution throughout the Great Plains is also similar, and a marked similarity exists at points along the Pacific Coast, although the actual amounts of precipitation may and do vary quite widely over these same areas. An examination of the diagram will at once show the wide variation in the distribution of rainfall through the growing or crop season in the various districts. Irrigation in Italy, South Africa and several other countries, is made necessary because the amount of rainfall during the growing season is deficient, although the annual precipitation may be and fre- *Monthly Weather Review, July, 1917. 230 Seasonal Rainfall in the United States. k 5 3J<7 ^^ HO/V ^T 3 *^^ * L_? L^ I /jo ^"eTZy^r— k^%X v^s 6/7^ ^7 /}//}/> — y ji />0/# V ye/t/ J0W g>ay uop S- 3> i/ O U / X J20 N /IOA/ \J /JO (2 J y JW ^ ?/"/ • au/?p "^^ yo't/ f - "^^>^j WW ( \ cyaj ) y°^s uop / J. l n S- ■£/?y /fynr *^> at/np * (P^r\ °^> fip/v ^^5^> /Jy JW_ VQJ\ i/or ^ s- 3 */ a ts/ Seasonal Variations. 231 ! §1? Jitttt jh v , 11IISI ililimilll * O/ympiet, Wash St. Paul - Minn. Bis mark, N.Dakefa Nashv/7/e 7 Tenn. = - ffl ,f jli 8 18 |H| _l| ? = fifilc -HI „11B Ilia -jalll I1h» iIIIIeIIbB iiA Jlllll.jll | lllili nil iiiiii ItlliililHllllill^ v San Francisco, Co/. Dubuqu e, Iowa f&pid C 1y,SDak. •% Murphy, N.C. '„ I ijl||| 1 _ " f 1 1 »8 ■ i' 5 <§ ?=31Bi I -'P 5 sill Ifll. mil *iiiiii..-.ii inim llllll Bill 111!.. flHlIilllp" _ San Dieao, Cat. Cain 3 III. Omahi 7, Neb. Bvslvn-, Mass. ^ = = ■ 1 /5 |||| || 1. J T 1! if |||§J§Jj |» |j 11 inn«|nnnnnmnnnnn|i -11 Hli«»m_l.Il 1 lllili 1 llafJIiliJ ?r Spakane, Wash. Helena , Mont. p5§ Lawrer *T? JIBIiillltl liU Iiiiii iiilti 1 1 llii sililliflili Winnemucca, Nev. Gatvesh '/7, Texas M/am ' 7 FIct. /ndfGwapdfsJnGf. = H . B ^mM b _L 1,„ llllll . 11 1 11 11 ■Binn 11 rmnm ^-llilflt .tit Hi l=llllllm-llll llllll llllll llllll llllll Jl II 111 111 i 11 11 II II III n 1. San/a Fe,HMex. New Qr leaps, La. IVi/miPa ten? Del. ^ Buffalo, N.Y , 5 -ft ~5 la? W \ a. ^ 1 " Penn. -, r kf\ = ■■ ~K- «I = = ll 5=|Il J, .1 llllll 1 Itll s.l.ll Ilia » IffSlllilllllb iillliklllio llllll iillll Mil IE illlil llllntllllld Fig. 128. — Monthly Rainfall in Per cent, of the Annual (see page 229). 232 Seasonal Rainfall in the United States. quently is as much or more than occurs in places which enjoy a quantity of rainfall adequately ample to support agriculture. Milan, the center of the irrigated district, has an average annual rainfall of slightly more than forty inches. This condition of insufficient rainfall during the summer months is occasioned principally by the effect of the prevailing winds, coupled with the seasonal land temperatures. £ -S3 )s ^ >- !*" ^ * ^ * ^ * r o £ Fig. 129. — Fluctuations of Monthly Rainfall at Madison, Wis. The North Pacific Coast, which receives the major portion of its an- nual precipitation during the winter, undergoes this condition because of the greater cooling effect of the land at this season upon the westerly ocean breezes. 114. Local Variations in Seasonal Distribution of Rainfall. — The total amount of the monthly rainfall is subject to much wider variation than that of the annual rainfall as might normally be expected from the nature of the occurrence of precipitation. These monthly amounts differ very largely from year to year and are subject to such wide Local Variations in Distribution. 233 TABLE 19. Precipitation at Madison, Wisconsin. Year Jan. Feb. Mar. April May June July Aug. Sept. Oct.' Nov. Dec. Total 1869 2.69 3.35 2.32 1.20 I 40 3.64 1.10 2.31 1.00 C.40 0.79 2.75 2.05 1.33 1.01 1.68 2.44 3.33 3.09 1.74 1.59 1.81 1 19 2.42 1.06 0.96 1.12 0.8i 2.22 3.59 0.16 0.69 0.62 0.17 0.11 0.30 0.77 2.80 1.89 0.97 2.33 2.82 0.60 0.58 1.64 0.70 2.05 3.07 1.64 2.35 1.35 1.43 0.40 0.60 0.95 2.80 1.60 0.30 1.19 2.54 1.75 5.42 1.74 1.64 2.12 0.82 2.35 4.34 1.01 1.84 2.01 1.38 1.94 1.05 0.46 0.26 0.32 0.92 2.42 0.42 1.26 0.59 1.46 1.11 1.87 1.28 0.97 0.28 1.79 1.70 0.74 3.40 1.50 1.12 0.92 2.30 0.39 1.51 0.79 3 85 2.96 2.18 2.07 0.9") 0.90 2.27 3.40 2.45 1.34 2.11 4.34 4.73 0.32 2.31 0.62 4.67 2.14 2.61 1.48 2.38 3.62 1.38 2.29 1.73 o'fa 2.38 2.67 1.94 1.32 2.77 0.60 3.50 2.44 1.74 2.13 1.80 1.62 1.12 0.14 0.47 1.92 2.41 1.J5 0.87 2.93 2.02 3.08 0.18 2.00 1.82 1.26 1.26 1.87 2.65 T 2.87 3.33 5.48 1.50 4.21 1 29 4.51 3.45 2.48 0.96 1.85 1.71 2.22 1.45 3.94 4.53 3.57 1.06 4.91 2.51 2.46 2.69 1.31 0.45 1.1/' 2.88 1.39 1.43 0.90 3.00 4.41 7.19 4.56 2.44 1.48 1.54 1.84 0.92 3.51 2.45 4.9:1 1.09 3.31 2.83 3.53 2.14 2.61 5.18 1.02 4.64 3.91 4.45 4.25 2.89 6.98 4.21 1.68 2.02 2.12 3.76 3.28 5.03 1.48 6.98 2.28 3.36 2.58 6.31 0.51 4.71 4.92 1.86 2.41 5.16 4.38 5.03 6.40 3.35 2.69 5.38 2.49 2.82 2.63 6.57 6.63 5.97 5.98 2.38 3.77 6.14 1.92 4.93 2 44 6.60 2.85 3.37 4.57 4.77 4.20 2.80 9.31 4.15 7.76 7.57 5.47 5.11 1.0S 1.48 2.95 2.00 7.72 3.69 7.61 6.69 3.94 0.59 2.69 4.03 4.40 Z. 64 3 20 2.40 4.27 1.39 2.85 2.b8 4.55 2.80 1.80 0.29 1.31 3.64 1.13 3.73 3.46 1.75 4.52 3.80 3.63 5.25 2.11 1.26 0.82 5.00 0.97 4.25 3.84 7.56 5.91 6.00 9.47 2.70 8.89 8.44 7.30 0.79 5.49 2.26 2.12 1.81 2.66 2.32 4.64 1.75 1.21 3.62 1.79 2.83 3.22 6.91 1.54 8.98 6.70 3.27 2.27 1.80 5.84 2.85 2.78 81 1.68 5.63 8.47 1.49 5.04 2.66 3.93 5.92 3.85 3.35 2.24 2.76 1.40 2.56 3.42 3.76 4.28 0.99 5.90 0.56 6.83 2.74 4.39 6.41 5.05 3.75 1.27 0.72 4.23 1.41 3.43 1.42 0.54 2.08 2.43 2.73 2.56 3.57 2.72 1.33 0.78 6.95 3.2>» 2.48 7.56 3.59 2.53 4.39 6.56 3.78 3.16 1 59 3.60 4.39 4.24 3.32 2.6S 4.00 0.47 5.11 2.54 5.46 2.08 3.41 0.64 6.54 2.79 4.44 8.17 1.91 2.39 4.25 4.05 2.29 6.67 1.04 1.93 2.62 0.38 3.. .9 2.67 4.21 0.91 4.29 1.73 2.43 3.35 2.89 4.16 4.18 3.54 5.93 0.58 2.04 4.69 0.7S 2.20 1.83 5.b5 5.62 4.32 3.49 10.69 5.73 3.48 2.66 2.09 3.07 0.60 1.96 1.44 1.96 1.59 4.12 3.78 2.50 1.68 9.12 4.14 3.79 4.60 2.37 2.21 3.18 1.68 T 4.59 1.49 0.36 1.85 1.77 0.58 3.03 0.86 3.08 1.58 4.44 2.49 1.23 ii.18 1.60 2.25 2.69 l.<4 0.64 0.91 0.63 2.92 2.49 2.53 3.09 0.48 2.97 2.34 2.05 0.53 1.35 0.76 2.15 3.51 0.40 2.31 2.81 0.76 6.02 1.C8 2.56 2.62 2.56 1.53 2.74 1.21 1.16 1.32 1.17 1.94 3.31 1.24 1.30 1.65 1.03 1.40 1 35 55 0.96 1.72 0.46 1.41 1.07 0.03 2.23 2.36 1.22 2.14 a. 28 1.59 3.56 0.89 1. .3 0.70 3.12 1.69 1.75 2.64 0.67 1.15 1.60 1.80 0.45 2.18 2.59 2.01 0.79 2.29 1.17 1.32 2.03 1.95 5.68 3.59 1.30 4.53 1.57 2.33 0.62 2.24 2.19 1.68 0.67 1.80 68 1.67 0.21 1.37 0.47 1.02 1.84 0.60 3.34 1.17 1.23 1.35 0.76 3.15 0.56 1.75 1.35 0.33 1.76 0.64 1.24 1.65 37 53 is;o 28 13 1871 i8ta 29.45 22 44 1873 2} 49 1874 , .... 1875 29.05 22 80 1876 36.15 1877 27.67 1878 39 54 1879 35.21 1880 1881 46.72 52.91 1882 1883 42.89 41.13 1884 49.19 1885 40.58 1886 28 78 1887 1888 38.89 23.06 1889..... ; 20.17 1890..... 36.98 1891 1892 24.24 37.10 1893 31.46 1894 24.59 1895 13.49 1896 31.35 1897 22.58 189S 31.91 1899 ,, 1 900 26.81 28.78 1901 20.24 1902 31.25 19D3 34.40 lt'Ol 31.25 1905 . 25.49 1906 32.38 1907 30.29 1908 25.67 ly09 30.83 1910 24.37 1911 32.72 1912 32.32 36.04 1914 28.17 1915 38.24 1916 35.33 Mean for48yrs.. 31.63 variations as to sometimes render the character of this occurrence some- what obscure, unless a number of seasons are considered, yet the same general character ordinarily prevails. Figure 129, shows the extreme and the average variation of the monthly rainfall at Madison. The monthly rainfall in the various months differs widely in amount and is by no means proportional to the total annual rainfall for the year. It is especially observable that during the year of maximum rainfall, viz: for 1881, the rainfall 234 Seasonal Rainfall in the United States. ======= fg^- . L --^\ tV 1 : \ t ! : r "$ ^*ih\L' \ *> ^ " ^ "1M lit" r=f — rn — — r— Ki-+ kNJr^^\ | N — - "l^^ 1 ^^;!-! T_ ! *> -^i± : f: : I \V— J-r I 1 . — :. _ -..- :§— t,\^J=tJ i!rlr^ . mi\g o^p Tit=^.^ SBLfOUl Ul IJ&JUIBtJ k ^ -! ■h 5 U) ' 4 H L t A \- ^ S s - <■ s :s T s 5 zr 10 ik^^s. . - ns. \ A 5 qj- & \ r y * in "& ^ -J_ 1 1 ^ |l: ■0 T^, ^% \ ** 4U44-S^f+t A ^r\R i --f~ *i i ! g' ^V L i i - ' M, ■ 5ii iSlhi x i X 1 *t^ "1 !* 5 ij , , JS b "i < ^,5jr s Mr- I it ^^-^ J; S a, lp= _L 1 SJi ^ ^J i^ < ! | 1 ==> IS Cj <5 s > saqou/ uj //vju/otf T= "**._ • T 5^ y t ^----, ± c £ t ^ ^ -tN + v — i-L-JI — ,- 1 3 __ l-^t? o S :::?r:::±"t---|— =1-^ ^ \ I - g- 1 L >&, — \ = - £ \| .: i^, — , - ::: ~e:i,::;::::::: E ::;::::::::3;:::§ fc> | :: <8 ;— ::-:::::::!!:==55=: :, 5=::: ^. 1 — £> :::::::::::::::::::^t-:: A::::::::^:::::::::5:::::£:::.| H 1, ■ "ds-^^^^^t, "-u ^ :":::::::::::::::::r::::::::::::.:*=4rf5i^...-:: -^::::| — : : " TC ^'Xt * b q ^ o 1 -iiiiJiiiiiiiMiiiJini m rv > 99LJ0UI Ul //tPJU/tPtf Local Variations in Distribution. 235 for April was almost as low as for April of the year 1895 when the total annual rainfall was at a minimum. It is also observable that the rainfall for August, 1881, was less than the rainfall for August of 1895. 40 30 to S20 /o r =H~ X ^ ^ 1* -\ 1 -f ^ L 7 t -t t r-s t +l ,) r i~ hi's^ J j^ p CT 4 ' - Z ! /_9// .JjT- '■+-<"' -d t I t -r*t * i 1^' t j""5 " -d ? - -j3J 7 i ^^ . hf - ■* (i~ f^ j* [895 »r J r J*"" ^^-^ P_I *--" ^ £ J ^ ? ^-I- r ~X- ^fit 3 ./?- ^ =f ^i^ x i_ 1/57/7 /^e^ M57- ^o/- A/c?y y"5 OS T. T5m . OS 1-5^ i 3 rf|* - ^■3^5 bJD^^i-s cy 2-5 2*. g 0> n 0) i-i ' • • • a • Q J' ■ t*- f* . - ■ q5" oT ©" of •"2.2 ■ OK 1^.2 CQ S? +3 p Cfi D55 •« • ■ -a k .fefefe« ■ |> . . .1- CO 03 02 CO CO -3 .3,3.3 . o 5 o tf 5 3 3 . ©1-55 DOOOOOOOOOO d .a .a P- „- = 0> <1> CD .P""*^ a a a^-Sco a a a • .2 • aaaa aaeaaaaSaa CDcU-5 l-j S 1-5 <) ■< 1-5 O • r-UH mm do ~ 3 oo tr 1- a ~ ~ oa m'o •5^ ^ :+ MCCCOlO 3:*-= * -■ C3 00 CO Oi §3^3 1-5 "5 "3 >-5 o>c>.2_; x ce v, * - Tl ^C3 t- X :3 X* O . - * io^oq • ■<- •>-ino ■ • • o its ■ o ■ • I-OOM-COOTOt- jo'o'Jo' xi o> o lO CO ^ ■ oo c- U 7 x - g CO !> " '£. x — " x x x ■-= _r"^ aT5l tuOo u ^ „• >> >» > a^XP^rjCScgo Sec 1 * 3 S S ?« cS 2 Sc§ _8 . . ."2 cs 3 :g a 3"S co.i..^eeaci)™aif-ira_ ; jj ^ — cs^,-i t -_^i.c5-^^:a) • . .Sss^oss .eafe - 5 5 Ph "HoSo.-; a a ^ -a s s a^ ^3^a=3 o ft M « ^5'gS.as o se "3 3 .. ^ cc >, x ^ ^ hi ± ^ L^ -- "T - ^ ^ ^ ~r — - — - c: — c: - -e -i- - x . ^ 13 t > h _ r -r. T', " H " . ": , — . V V .V . ^ ^ "^T ^ "-T 1 ^ - n ^7 -^ t_, n_, -ft tK a ->r ,n, *-*-/•■ ■--. — Frequency. 249 then when comparing stations where the time of reading is different, they are to an extent uncertain. Such a study, when it includes all of the data which are pertinent to a given locality, will furnish a reason- able basis for the estimate of local storm intensity. 123. Frequency of Intense Rainfalls. — In general the frequency of intense rainfalls increases with the increase in the average annual rain- 4 8/2 Frequency, Years Fig. 134. — Average Frequency and Average Intensity of Maxi- mum One Day Storms (see page 250). fall of a locality for the reason that the conditions favorable to in- tense rainfall are more common under such conditions. For example, intense rainfalls are much more common in the State of Florida where the average rainfall is about 55" per annum than in the state of Wis- consin where the average rainfall is about 32" per annum, or in the State of Ohio where the average rainfall is about 36" per annum. This condition is due however not only to the conditions favorable for rainfalls in Florida but also to the West Indian hurricanes which frequently cross that State and which commonly bring about con- ditions favorable for torrential rainfall. The rainfalls of Wisconsin 250 Great Rainfalls. and Ohio are a result of the greater cyclonic storms which in general are not so productive of brief and intense precipitation. Occasionally, however, conditions favorable to high rates of precipitation do occur in Wisconsin and Ohio as is evidenced by the intense rainfall of July 16, 1914, shown in Fig. 133, page 246, and by the rainfall of ii/4" which occurred at Merrill, Wisconsin, within twenty-four hours in July, 1912. In the semi-arid regions where the average annual rainfall is very low, exceedingly intense rains of limited extent, termed cloud bursts, occasionally occur. On August 9 to 11, 1909, 13.38" of rain fell at Monterey, Mexico, within forty-eight hours, and between August 25 and 29, 1909, 21.61" of rain fell within ninety-eight hours. The an- nual rainfall at this station for 21 years previous to that date averaged 19.86", and in the four days of the second storm more water fell than usually falls in an entire year. 5 It is evident therefore that the in- tensity of the local rainfall which may occur bears no direct relation to the amount of annual precipitation. Figure 134, 6 page 249, is a study of the average frequency and average intensity of the occurrence of one-day storms at various selected stations where long records, ranging from forty-two years at Galveston to sixty- seven years at St. Louis, were available. These curves are constructed as follows : For the Galveston curve, based on forty-two years of record, the probable maximum storm that will occur each year is taken as equal to the average of the forty-two maximum storms that have oc- cured during the period, and the average of the twenty-one maximum storms is taken as the probable maximum storm that will occur every second year. Other points on the curve are established in the same manner. The flattening of the curves, due to'the close agreement in intensity of the several storms in the records which are included in the average for the fourteen year period, gives assurance that the curves are typi- cal, and that the probabilities that a storm such as is likely to occur at Galveston may occur at Cleveland are very remote if not physically impossible. 124. Local Intensities of Short Duration. — The records of intense storms of short duration for any locality may be platted with the in- tensities as ordinates and with the intervals of time at which such in- 5 See Eng. News, Sept. 23, 1909. 6 Prom data furnished by A. E. Morgan, Chief Engineer, Miami Conservancy District. See also Eng. News, Vol. 77, p. 150. Local Intensities. 25 i e lb <0 0) . . • • F0-. C < i ^^ ?C •J I • • • 6 ' • * \ X •a | •3 • ^ • 6 £, »4 < •^ !i i 4 ■ ,7 » 4 1.4 M f* |* < |4 :« ;»* »2 L .p ! 5 A (2 \ 1 \ < ! i i >2 ~-^d •4 t ?, 1 • ? I 4 ! I 2 6 : f • 4 1 •« ' >4 ••* ' i4 is ; 4 » B « < i-' • 2 4V7 6e (6 i ! 2 ! 1 2 (I /V ■ J. 1 | \ to 3 A $ \ \ ■e drawn to average the points or to include them all, as the investigator may desire. In the case of the smooth curves the indication of fre- quency at certain intervals may be somewhat greater or less than the absolute experience, but if consistently drawn may possibly indicate more nearly the truth which would be 'developed by a longer series of observations, by giving greater weight to the preponderance of evidence over a single or a few observations which mav be more or less extreme. Frequency. 255 Having platted the points as above outlined and adjusted the fre- quency-interval lines as indicated, it is obvious that a horizontal line through the frequency of one storm per year will indicate by its inter- sections with the various curves, the intensity which must be expected each year at the various intervals of time. It must also be noted that 20 30 40 50 60 70 80 Interva/s of Time - Minutes 90 IOO I/O 120 Fig. 138. — Frequency of Intense Rainfalls at St. Paul, Minn, (see page 254). the intensity at the various intervals of time for any other term of years can be determined in the same way by the intersection of these curves by a horizontal line drawn through .a point below the frequency of one storm per year determined by dividing one by the number of years for which such curve is desired, as indicated in Fig. 138. Such curves de- termined for St. Paul are platted in Fig. 139, page 256. T These curves indicate a certain general progressive distribution which gives at least i This general method for determining frequency curves is that outlined by Metcalf and Eddy under the heading of "Frequency of Heavy Storms." They have also discussed "Intensity of Precipitation" at considerable length. See ^'American Sewerage Practice," by Metcalf and Eddy, Vol. 1, pages 220 to 234. 256 Great Rainfalls. some indication of the probable frequency of the maximum curve first developed in Fig. 135, page 251. By platting interval curves in terms of intensity and years of occurr- ence as determined from Fig. 139 (see Fig. 140), and extending these curves beyond the limits of experience (shown by dotted lines), an es- timate can be made of the probable limiting time of the maximum curve which, as shown in Fig. 140, may be estimated as representing a. 10 zo so 40 50 60 JO SO Infervaf-s of T/me - Minc/fes 90 IOO //O IZO Fig. 139. -Intensity of Rainfall at St. Paul for- Various Frequencies (see page 255*). probable frequency of once in from 90 to 120 years. As previously noted, however, any attempt to extend actual experience beyond the term of years in which such experience is acquired is speculative and must be taken as indicative only and not as in any sense established. It is important that the engineer should also recognize the limiting value of the frequency investigation above outlined. With the present knowledge available, it furnishes perhaps the best basis for the study of this subject. Like the investigation of the annual rainfall at Boston, discussed in Sec. no, a similar investigation for a similar period of years in any given locality would doubtless give quite different con- clusions as to frequencies. Frequency. 257 It should also be noted that the rates of rainfall used in the investi- gation, especially for the longer intervals of time, are average rates and not uniform rates, and are therefore somewhat misleading when these longer intervals are considered. For example, the actual occurrence of the rainfall of August 8 and 9th, 1906, at Madison is shown in Fig. 141 with the uniform rates of occurrence platted below and the average 10 Mjpyl-^ _-r$=^ T 1 1 I Jo MW«p - ^^=- ±*zi 60_Mmufe_ Ra/nfa/J_ 30 40 50 60 70, 8O 90 Infervate of Occurrence - Ye f "V * 1 < + J s> ♦■ i >* r^ r J *- ^ t ft I 1 *♦ I- ■* - r r ^ *# * i h ^ ■y — ' ■■ J r? ^*J & ' ti5 * f i t £ * ■ T J * *» - f h % r "^* ' r ii < , Ft ^ — » 0A JO- /* J/J* £A JO" J* Fig. 143. — Talbot's Study of Maximum Rainfall Intensities of Short Duration (see page 259). investigations are given by the following formulas in which i is the rate of precipitation in inches per hour, and t is the duration of time ex- pressed in minutes : In this tabulation are also given the formulas of Prof. Talbot, reduced to similar units for comparison. 262 Great Rainfalls. TABLE 28. Formulas for Maximum Rainfall. Formula Author Remarks 105 A. N. Talbot 10 Ordinary maximum A. N. Talbot Maximum occurring once in about 15 years A. N. Talbot Maximum exceeded 2 or 3 times per century E. W. darken To be expected each year E. W. Clarke Exceeded once in 8 years E. W. Clarke Exceeded once in 15 years Kuichlingia Shermani-- (Chestnut Hill) . Maximum Sherman Ordinary C. E. Gregory Ordinary severe storm C. E. Gregory Winter storms C. E. Gregory Maximum io Rates of Maximum Rainfall. A. N. Talbot. The Teclmograph, 1891-2, page 103. Also, Rainfall and Runoff in Relation to Sewerage Problems. W. C. Parmley, Jour. Assoc. Eng. Soc, 1898. ii Storm Flows from City Areas, and Their Calculation. E. W. Clark. Eng. News, Vol. 48, p. 386. is Rainfall and Runoff in Storm Water Sewers. C. E. Gregory. Trans. Soc. C. E., Vol. 58, p. 458. Also, Maximum Rates of Rainfall at Boston. C. E. Sherman. Trans. Am. Soc. C. E., Vol. 54, p. 173. 1. 1 = t + 15 180 2 i t + 30 360 o i t + 30 4. /54~ t 5. /162" i= V t /324~ 6. i'=V t 7. /120" i= V 20 + t 38.64 g : t,0. 08 7 9 25.12 to.087 12 10 £ t«- ■> 6 11. i tO.o 32 1° : to.s Rainfall Formulas. 263 Figure 144, page 264, shows a platting of a number of formulas to- gether with some curves for maximum rainfall rates which have been devised by various writers but which have not been reduced to a mathematical expression. The variation in the formulas and curves is due to the fact that they were derived from records of different localities and in some cases for quite different frequencies. In this figure, Curve 8 was constructed from the combined records of excessive rainfalls in the cities of Bos- ton, Providence, New York, Philadelphia and Washington and repre- sents the observations for an aggregate of about seventy years, and was the curve adopted by the engineers who made the report on the sewerage of the District of Columbia in 1890. An examination of the various curves shown in Fig. 144 will make it manifest that the application of any single formula to the determina- tion of probable local rainfall intensity is liable to lead to very errone- ous results, unless it is first determined whether or not the formula actually applies to the particular condition of the locality. In all cases where the problem to be solved is of importance, an independent inves- tigation should be made, or the origin and basis of the formula or in- tensity curve considered should be ascertained and its real application to the particular locality determined. 128. Rainfall for Longer Periods. — Professor F. E. Turneaure has investigated the local rates of rainfalls that have occurred during longer periods and within certain general geographical boundaries, and has embodied the maximum results of his study in Fig. 145. Concern- ing the investigation on which this diagram was based, Turneaure says : "The records cover the period from 1871 to 1906, and all rainfalls are represented which exceeded in amount five inches in twenty- four hours, and, from 1894 to 1896, all those which equaled or exceeded two inches in one hour. As far as possible, the same storm is repre- sented but once for any one state, although records may have been re- ceived from several stations ; and furthermore each storm is counted as a one-day storm or a two-day storm, but not both. A one-day storm is one in which all the rain falls in a meteorological day, that is, from 8 P. M. to 8 P. M., and in a two-day storm, all the rain falls within two such days. A one-day storm may therefore have fallen in a few hours, and likewise a two-day storm, so that the figures given do not necessarily represent the maximum rates. However, by taking the' maximum from among a great many records the figures thus found 264 Great Rainfalls. 60 90 /20 t = T//7?e /n tf?//7u/es. /80 Fig. 144. — Intensity Curves for Storms of Short Duration (see page 263). Local Rainfall Intensity. 265 for the one and two-day storms will approximate the maximum for twenty- four and forty-eight hours. The one-hour rates are well de- termined. The number of times a rainfall has exceeded the given amounts is an indication of the frequency of heavy storms and also to some extent, of the reasonableness and reliability of the maximum fig- ure. Those states having the highest maximum rates are those where heavy rainfalls are the most frequent. 24 A/rapas5/VC. o Ju/ /A. /SI 6 20 16 Ga/ves/on Tex. Ocr. 8. /SO/ 'ju//3 /900 Son Marcos. Tex. Ocr 2. 19/3 1 12 1 $1° IC : -' Merr//f W/s Q J.jtf ' Ju/ 24J t^\ =z- Ml", rOl qjj^X — ■ 8 32- P \J7~Sra' e 5 jW ec_ v^ h j£r~" j^> 4 8 16 24 32 40 43 Dura //on of /-?o/n/a// Hours Fig. 145. — Turneaure's Curve of Local Rainfall Intensities (see page 263). "The curve for the Northern and Central States is somewhat ex- ceeded in a few states, but for most of them it represents rainfalls but little greater than those which have already been observed and which may occur again at any time. The curve for the South Atlantic and Gulf States represents the maximum recorded rainfalls for all the states of this group except Louisiana, for which the records far exceed those of any other state." 13 To the original figure have been added the rainfall at Cambridge, Ohio, July 16, 19 14, and at Altapass, North Carolina, for the maximum twenty-four hours of July 15-16, 1916, and a few other records of ex- treme rainfalls. As noted from the above quotation, the curves were not drawn to show extreme maximums but rather the probable maxi- 13 Public Water Supplies. Turneaure and Russell. 2d Ed., p. 49 et seq. See ak:o Table 7 for detailed study on which diagrams were based. 266 Great Rainfalls. mums for perhaps a twenty-five year period. The added data show that to include extreme intensities, the curves would all probably have to be raised considerably and that even for a twenty-five year period they might have to be altered somewhat in the light of the twenty years of observations which have elapsed since the end of the period on which the curves are based. 129. Intensity Over Large Areas.- — The local intensity of rainfall which has been previously considered is that determined from single stations or groups of stations and is therefore applicable only to limited areas. Such intense rains never extend over large areas, and the esti- mates based on such observations cannot be applied to any consider- able drainage areas. It is to be noted, however, that it is by no means certain that the maximum intensity recorded by a given gage in a cer- tain area represents the maximum intensity of rainfall that has oc- curred on that area, and indeed it is probable that the records in prac- tically all cases are actually below the maximum that has occurred as the gage area is such a small part of the area which any storm covers. This fact somewhat offsets the error in the application of the data to areas of considerably greater size, which would not be warranted other- wise. In the consideration of the flood flows of streams and the maximum discharge of considerable drainage areas, the factors of both intensi- ties and area become important, and the engineer must again have re- course to the records of the Weather Bureau. In the great storms of March 24-27, 1913, which were the main cause of the flood of the same dates, the ground over most of the re- gions where floods occurred had previously been saturated by the storm of March 20-23, 1913, which has been illustrated in Fig. 31, page 70. This storm was almost immediately followed by the storm of March 24-27 although there was a sufficient cessation of rain to make the two storms entirely distinct. The extent of the storm of March 24-27 for each of the days included is shown by Fig. 146, page 267, and its distribution of intensity over the area particularly af- fected by the floods is shown in Fig. 147, page 268. By measuring the areas surrounded by the various isohyetal lines, the distribution of the rainfall of this storm for different intensities can be approximately determined ; and by a similar measurement of similar maps drawn to show the distribution of the maximum rainfall for one. two and three days, similar data can be approximately determined for such periods. Figure 148. page 268, shows curves for the distribution of intensity Intensity over Large Areas. 267 ^£t~ 5 °> Y^£~§*&^«r a ^^S^Sj?^?^?^ <§-> -c: jo "^=s|^S§S fc ^11 ^iiii IKlKk^ if /s ^-^V^^IS^ t|g|ha=Xj^ ?pb^ '(^>3£g=&? ^5d5w)^" "^r — -^S^Sfc^SE 1 ?*^: ^Sr5P; js. ^=VyL <£,!V c> fS 50 y- M=C •"3 1 Or* fe*Q= "^ jl)" N=^X ^->^> ^ <: ji----^ JF-l^p^S^ jtjtS isp||2i "o \r^l O v *\j£0) ) / r-S5 \ iu.'s r % i r \ kJpM/ /> ^ f/ o V 7 ) £? ^Z-^- f &/i ?£: -/si 1)J s 1 <^^ 1 «" £s ^^fes^^^v J? & :^^^^f!3^S Ci \ to ■* ^l_ l^aE^rl^rif jsSr. X^ •i ^3 ^I^Sa J*" 1 ^xTjL^pd\ V \VyA ^s.v ^ 5: \ 1=1 —J/0 r--' f^- 71 CV? ^-^_, // ^ 7 Y^O ??c to 1 *? -5 S / r « -^ < >R . J ? s 45 gC^-WK/ "5 ij °^ xnm <_i/\) .-±r^Q> ?^ 1 ( ^<\ : ^^-^J i 4=^ i-dS^i^^ "ftp >v f-=~" J V vY Ut-Ql >J i&rt^f—h 2 ii^^BjSX §P/ V<^ ~^~~^ir~-~ / §"^^ °> o \ / -S: >^r -"-* -_ g rlpli- ^"^e^:-3-_ci ^T^^gil ^i ■S±^K£^d+?£lZ Q ^^iiw ^F a^fcp^oU p •viK \y{ I LZyE~ ^3>>d~ ^^tt\ J) -xa/y / yw (-r-dzf^T^J s^iM-J j^&L^-t v£> /P /yfepJFl .x/ij^ / jSv? J c '^~k? z //y s> a ^hskj// s «j $ ^-K^j "^ 270 Great Rainfalls. of this storm for periods of one, two, three, four and five days. 14 In the investigation of the problem of the maximum storms which might possibly visit this area, it was soon ascertained that a storm on essen- tially the same path had occurred in October, 1910, but that the most intense rainfall had occurred westerly from the center of the area of intense precipitation of the storm of March, 1913. 'Y^onsas dry Fig. 150. — Isohyetal Lines for Storm of October 4-7, 1910. The path and geographical extent of the storm of October, 19 10, is shown in Fig. 149, page 269, and the isohyetal lines are shown in Fig. 150. 130. Excessive Rainfall of the Eastern United States. — After the great flood of March, 19 13, an investigation of both rainfall and flood records was undertaken by the Miami Conservancy District in order to determine whether the flood that had just occurred might be re- garded as the maximum that might ever be expected or whether the flood protective work should be designed for a flood of greater magni- tude. This work, which was undertaken by the Morgan Engineering Company under the direction of Mr. A. E. Morgan, Chief Engineer, is believed to be the most complete and thorough investigation of the problem of the intensity of rainfall over extended areas that has ever 14 From data furnished by A. E. Morgan, Chief Engineer Miami Conserv- ancy District. Excessive Rainfall. 271 -been attempted. While the research was undertaken with special re- gard to Ohio and the adjacent country, it covered quite thoroughly the eastern half of the United States and will furnish a basis for reliable estimates over this entire area. As a basis for this study, the rainfall records were abstracted for all storms in the United States east of the 103 ° of longitude, including all rainfalls that equaled or exceeded the following limits : For stations where normal annual rainfall exceeded twenty inches, all storms where the total rainfall for a single day equaled 10 per cent or the total rainfall for the entire storm equalled 15 per cent of the normal annual rainfall. For stations where normal annual rainfall was below twenty inches, -all storms of one inch in twenty-four hours or four inches for the total storm. The investigation included some 3,000 stations. Some of the most valuable results of these studies relative to local rainfalls are embodied in six maps showing the maximum rainfalls in each of the quadrangles in one to six days. 15 These maps have been summarized in Figs. 151 and 152, pages 272 and 273. In Fig. 151 the maximum rainfalls for 1, 2 and 3 days are shown in each quadrangle, and in Fig. 152 the maximum rainfalls for 4, 5 and 6 days are also shown. These maps include only data available to Dec. 31, 1914, and for stations having rainfall records for five years or more. These investigations include 2641 storms. Of ■these 1,236 were found to be storms registered at only single sta- tions and therefore of no great geographical extent. Nine hundred -and ninety-six storms were recorded at from two to five stations, and 409 storms were recorded at more than six stations. For the purpose of the investigation, only storms that covered 500 square miles or more and that had a total precipitation of at least 20 per cent of the normal annual rainfall were studied in detail. Of seventy-eight such storms, the twenty-seven largest were chosen for final consideration. The geographical location of these storms as shown by the limiting isohyetal lines of five inches of rainfall is given in Fig. 153, page 274. 131. The Application of Data. — In considering the rainfall data available from areas widely separated geographically, and conse- quently greatly differing in climatological conditions, it is important to determine what data may be regarded as applicable to local conditions. It has already been pointed out that local rainfall is induced by cer- 15 Storm Rainfall of Eastern United States, by the Engineering Staff of the District. Technical Reports, Part V. The Miami Conservancy District, Dayton, Ohio, 1917. 272 Great Rainfalls. tain conditions among which the most important are the directions, paths and intensities of the storms to which the locality is subjected and its situation relative to the sources of moisture from which the rainfall must be derived. While storms of great intensity occur far 18" I7~~ 16" /5 Fig. 151. — Maximum Depths of One, Two and Three Day Rainfalls. from the location of areas of maximum evaporation, it is evident that such distances limit to a considerable extent, the frequency of occur- rence, the duration of high intensities the extent of area over which such intensities may occur, and the maximum intensities to which such localities may be subject. While the storms of July, 1914, in Ohio (see Sec. 121) and of July, 191 2, in Wisconsin (see Sec. 123) are equal to many similar storms which have occurred in the Gulf and South Atlantic States, it is believed that such storms are approximating a maximum, for those localities, and that no such storms as those which occurred in the Carolinas in July, 1916, in Porto Rico on August 5-9, 1889, or at Mont- Excessive Rainfall. 273 erey, Mexico on August 25-29, 1909, are physically possible in Wiscon- sin, Ohio or other regions similarly located. It is also important to note that the greatest local or general storms are likely to occur during seasons when evaporation and con- 18 /7 /6 /5 M 13 12 II 10 9 L 103' /Or 99' 97' 95' 93' 91' 89' 87' 85' 83' 7 6 5 4 3 2 I ?/• 19' 77" 75' 73' 71' 69' 67' 103- f8 ^ /7 39- l6 SY J5 35 /4 93' /3 9r /2 89' // 87' /0 85' 9 83' Bf 7 79 ' 6 ir Fig. 152.— Maximum Depths of Four, Five and Six Day Rainfalls. sequently atmospheric moisture is' at a maximum, that such conditions appear essential to their occurrence, and that in consequence it is im- probable that even such excessive storms as are known to occur can occur during cold periods, especially in the north when the ground is covered by a deposit of snow. While a storm similar in intensities to the great storm of October, 19 10, must be anticipated as a future possibility at other localities in the country adjacent to its path, it is unlikely that such a storm will occur during the early spring under conditions of materially lower tem- perature. It is not therefore to be anticipated for any given locality Hydrology — 18 274 Great Rainfalls. that with the lapse of time, storms are bound to occur which will be equal to any other storms which may have occurred in any other lo- cality. For each particular locality there are undoubtedly limits which it is physically impossible that rainfall can exceed in intensity, dura- tion and extent. What those limits may be cannot be determined with Fig. 153. — Limit of 5-inch Isohyetals of Great Storms of Eastern United I States. any great degree of exactness on account of the short time for which rainfall records are available, but the observations of the flow of streams in other countries for many centuries, bear out the conclusion that such limits do exist and that they can be approximately determined. When such flood records are available for hundreds of years, the flood heights of the several greatest floods agree within a few feet of each other, and in such long time records no one flood is found to greatly exceed other extreme floods. The greatest flood that occurs once in a thousand years does not greatly exceed the maximum flood of one hundred or even of fifty years. It is reasonable to assume that the Frequency of Storms. 275 great rainfalls, which are the principal underlying cause of the floods, will not in the lapse of centuries vary to a much greater degree than the floods they produce. 132. Frequency of Storms of Various Magnitudes. — In the studies of maximum rainfall undertaken by the Morgan Engineering Com- pany for the Miami Conservancy District, the country east of the 103 meridian was divided into districts on the odd degrees, thus giving 133 two-degree quadrangles. (See Figs. 151 and 152, pages 272 and 273.) To determine the frequency of storms of various magnitudes as well as the maximum storm which might be expected to occur within a given period of time in each quadrangle, 16 the years of record for each of the several stations within each quadrangle were totaled, as were also the oc- currence of storms of a given intensity. By dividing the total year of ex- perience in the quadrangle by the number of storms of the given inten- sity, the time interval was estimated for that particular storm intensity. By repeating this process for storms of various intensities, estimates were made for which frequency curves for each quadrangle were con- structed. The quadrangle which includes the Maimi River is shown on Fig. 154, page 276, and the frequency curves for this quadrangle, based on estimates made as above described, are also shown in the same figure. From these curves the frequency of the maximum storm intensity for one or more days within the experience of the Miami quadrangle can be estimated, and the probabilities of greater storms within terms of years beyond the experience of the area can be approximated by their extension. It will be noted that the general form of the curves is simi- lar to and vertified by the local intensity curves previously shown in Fig. 134, page 249. In order to compute the intensity of a storm that will probably occur once on an average of 50 or 100 years, the sum of the record years of all stations in each quadrangle was divided by the number of years in the period considered. For example : if a total of 360 storm years were on record in a given quadrangle, the average maximum storm for a 50 year period would be the average of the seven (7.2) maximum storms experienced, and for a 100 year period the average of the four (3.6) maximum storms experienced. For this purpose no sta- tion with a record of less than 10 years was considered. The results of these studies are embodied in some 24 "Isopluvial" charts for 15-year, 25 year, 50 year and 100 year periods, and for 1, 2, 3, 4, 5 and 6 days rainfall for each period, all constructed on the above 16 Eng. News, Vol. 77, p. 15. 276 Great Rainfalls. principle. 17 Maps so constructed are perhaps reasonably indicative of conditions which may be expected to obtain. They represent an attempt to analyze a most complicated subject by using such data as are now 30 AO 50 60 ^reepuency, rears Fig. 154.— Intensity Studies for Miami Quadrangle ie (see page 275). available but which are admittedly insufficient for drawing definite con- clusions. The reliability of this method of investigation for determining the fre- i" Storm Rainfall of Eastern United States. Technical Reports, part V. Miami Conservancy District, 1917. Frequency of Storms. 277 quency of maximum rainfall occurrences depends at least partially upon the actual occurrence of the maximum extreme conditions within the ex- perience of some of the stations within the quadangle or district consid- ered. If the occurrence of rainfalls of great magnitude is of a periodic character for correct results the period of maximum intensities must be included in the record, and if occasional exceptional conditions will occur at very rare intervals, they will not be discovered unless very long records are available. This method while an interesting basis of investigation, cannot be regarded as strictly correct for if correct it should be possible to obtain 300 years of experience from 300 one-year observations at 300 separate stations within a single quadrangle. It is evident that as all such limited areas must be subject to similar meteorologic conditions, an exceedingly dry or an exceedingly wet period would affect all of the stations and thus give erroneous conclusions. It is evident that the occurrances at any station in a district having similar meterological con- ditions may be taken as a fair criterion of what may occur at other sta- tions in that district ; but the extreme occurrences at any one station will not fairly represent the extreme which may occur at any one station during a period equal to the sum of all the periods for which observa- tions have been taken at all the stations in the district. 133. Time-Area-Depth Curves for Major Storms. — In the investi- gations of the Miami Conservancy District, ls the study of major storms included among others the nine major storms listed in Table 29. TABLE 29. Major Storms Considered l>y the Engineers of the Miama Conservancy Dis- trict as Applicable Thereto. Index Date Center of Storms a May 31-June 1, 1889 Pennsylvania b Julyl4-16, 1900 Iowa c Aug. 26-28, 1903 Iowa d June 9-10, 1905 ". Iowa e July 5-8, 1909 Kansas f July 19-22, 1909 Michigan g Oct. 4-6, 1910 Southern Illinois h March 23-27, 1913 Ohio i August 17-20, 1915 Arkansas The time-area-depth curves of these storms for one, two and three day periods are shown in Figs. 155, 156, and 157, pages 278 and 279. It should be noted that all of these storms, with the exception of that which actually produced the great flood in the Miami Valley, occurred is Report of Chief Engineer, Miami Conservancy District, Vol. I, p. 87 et seq. 278 Great Rainfalls. late in the season and it is improbable that storms equal to the three maximum will ever occur in the Miami Valley early in the season with frozen or snow covered ground. q Hi \\ \^ \\ x^. *, \ ^r^^jr^ ^^k s— -___ ~~ J~fT :^5 ^™ -~ ~-~- zz~~-- """^^t: ^rj± p=r? E= =^r=r === =^=; yj-e- / Z 3 4 5 6 7 8 "jform fireo in Thousands of Square M/'/es Fig. 155. — Time-Area-Depth Curve for 24-Hour Storm. 10 14 M 1 1 ^ \>\ :b< c ^^ Sfr^^ ~" v ■•;'» ^ ~ "- — — — "^sr^ fS^=Sv == * O / Z 3 4 5 6 7 8 9/0 Storm /7rea in Thousands of Square Afi/es Fig. 156. — Time-Area-Depth Curve for 48-Hour Storm. Nevertheless the uncertainties involved warrant the use of adequate factors of safety in all designs involving the safety of life and prop- erty. 134. The Study of Extreme Conditions of Rainfall. — In estimat- ing extreme conditions additional light can be obtained by examining the extremes at other stations within a district having similar meteoro- logic conditions and basing maximum and minimum estimates on limits Stucfy of Extreme Conditions. 279 fixed by similar occurrences within the district ; but the frequency with which such events are likely to recur can at best be but roughly esti- mated. The extreme conditions of the one day rainfall for quadrangle B-12 in northern Wisconsin, shown in Fig. 151, are largely fortuitous and are scarcely liable to recur at the same locality in perhaps the next one hundred years or more but are liable to occur at any time at some other point within Wisconsin or in adjacent states. In the same way the extreme intensities of the storm of June, 1889, at Alexandria, Louis- iana, shown in quadrangle L-13 will scarcely be expected to obtain V *1 II b \ — ■ \ \ s\ \ ^.H ^ -. 1 \ 1 x r ^:r -"^:r~_- —9 — ■k . ^== — b > — — - -~h — e -- — r =^= — .c^—--- ■ ■ — - ~"— — -__ ~~ f ~ — — — ■ — — — - " 0/Z3456789/0 Storm fireo in Thousands of Square M/'/es Fig. 157. — Time-Area-Depth Curve for 72-Hour Storm (see page 277). again at this locality for many years ; but it seems quite probable that a similar storm may occur at any time within the Southern States as did the storm of July, 191 6, in the Carolinas which, had it occurred at the time of the construction of these maps, would have materially modified the intensities shown for the quadrangle G-8. The maximum depart- ure from the mean annual rainfall at Madison is -f- 21.3" and — 18.14". It seems quite possible that any station in Wisconsin may experience departures of equal magnitude, but the combination of all the station experience in the State would not give the frequency of occurrences that the sum of those observations represent, and would lead to a false idea of the meaning of the data. The extraordinary rainfall of August 8-9, 1906, at Madison, Wis- consin, was found to be the storm of maximum intensity for periods of from 30 to 120 minutes for stations in and adjoining the State of Wis- consin, as shown in Fig. 142, page 260. It is evident that the frequency at which such a storm must be expected to occur in any locality in Wis- 280 Great Rainfalls. consin cannot be definitely or even approximately evaluated with the limited records available. The combined time of record shown in Fig. 142 is 183 years, but in comparison with the estimated length of the maximum experience at St. Paul (Section 125) , this would be too low an estimate of frequency for the Madison storm. The necessity of long time records to cover extreme variations in annual rainfall is illustrated by the curve of progressive means for Southeastern New England (see Fig. 117, p. 211). This curve is below the mean for 26 years from 1833 to 1858 inclusive, and there are 52 years between its minimum in 1837 and its maximum in 1889. It is probable that frequency determination and intensity-duration-depth maxima, even when considered for extended areas, may require a sim- ilar or even a greater time for their full appreciation. It seems prob- able therefore that the average length of record of the various stations for which observations are available especially in many parts of the area covered by Figs. 151 and 152, is not sufficient to fully cover the long time probabilities, and that in some cases the occurrence of un- usual and rare storms, on account of the time limitations of the data available, unduly accentuate the occurrence of intensities in certain dis- tricts and underrate the probabilities of similar occurrence in other dis- tricts. 135. General Conclusions. — It is important that all should recognize our unfortunate but necessary ignorance of the frequency with which such extraordinary events obtain, and that we are entirely unable to for- mulate any exact rules for such occurrences. In many cases the con- trolling element of cost will not permit works to be designed to care for such unusual conditions, and in cases where property loss alone is to be considered and where no loss of life is uivolved, the extreme conditions must be ignored in the design with the understanding that occasional loss is more desirable than unwarranted expense. Deductions that can be drawn from extended studies on lines similar to those above dis- cussed, especially when the studies apply to the older parts of the coun- try where considerable data are available, are believed to furnish an adequate basis for- engineering design. Such uncertainties as remain must be covered by adequate factors of safety. LITERATURE. Excessive Rainfall. Eng. News, 1S94, "Vol. 31, p. 409. Rate of Precipitation, Ithaca, N. F., J. H. Fuertes. Eng. News, 1894, Vol. 32, p. 22G. Maximum Rates at Boston, D. Fitzgerald. Eng. News, Vol. 11, May 31, 1884. Literature. 28 1 Excessive Rainfall in Neio York City, 1S99-1905, C. H. Nordell. Eng. News, 1909, Vol. 61, p. 265. Maximum Rainfalls at Mobile. Ala, 1872-1891. Eng. News, 1901, Vol. 46, p. 26. Record of Rainfall of the American Continent at Jewell, Md., July 26 and 27, 1897, Kenneth Allen. Eng. News, 1902, Vol. 48, p. 190. Report on Floods of May and June, 1901, E. W. Myers. Eng. News, 1902, Vol. 48, p. 102. Maximum Rates of Rainfall at Boston, C. E. Sherman. Trans. Am. Soc. C. E., Vol. 54, 1905, p. 173. Record Heavy Rainfall at Sidney, N. S. W., C. H. Wilcox. Eng. News, 1910, Vol. 83, p. 171. Remarkable Fall of Rain in Arizona and Sari Diego. Eng. News, 1898, Vol. 39, p. 298. Rainfall and Runoff in Relation to Sewerage Problems. W. C. Parmlee. Jour. of Assoc. Eng. Soc, 189S. Storm Flows from City Areas and Their Calculation, E. W. Clarke. Eng. News, Nov. 6, 1902, Vol. 48, p. 386. Rainfall and Runoff in Storm Water Seioers, Chas. E. Gregory. Trans. Am. Soc. C. E., Vol. 58, p. 458, June, 1907. Variations in Precipitation as Affecting Water Works Engineering, C. P. Bir- kinbine. Jour. Am. W. W. Asso., Vol. 3, 1916, p. 1. The Relation of Rainfall to Mountains, W. H. Alexander. Monthly Weather Review, 1901, p. 6. The Theory of the Formation of Precipitation on Mountain Slopes, Prof-. F. Pockels. Monthly Weather Review, 1901, p. 152. See also Mechanics of the Earth's Atmosphere, Smithsonian Miscellaneous Collection, Vol. 51, No. 4, Article VIII. Effects of Mountains on Humidity , Cloudiness and Precipitation, Dr. Julius Hann. Handbook of Climatology, translated by R. De C. Ward. The MacMillan Co., New York, 1903. Rainfall in England in Relation to Altitude, W. Marriott. Quar. Jour. Royal Met. Soc, Vol. 26, 1900, p. 273. Phenomenal Rains the Cause of Southern Floods. Eng. News, Vol. 75, 1916, p. 183. Long-Time New York Rainfall as the Basis for Sewer Design, O. Hufeland. Eng. Rec, Vol. 76, 1916, p. 393. Southern Rains \ H HOT SPF 3ARNET/I INSO / BOISE (JMOSCC 1 w / / FA ' \ \ I COLFAX 3 "1 Z 01 Rl <5-r ON 4 /1®DAYTON / OMEROY DETROIT £ E« >F,ENDLETON | ill 1 / LA CROSSE V y ± i ...L.i- 1 L ^ / EVVI5T0 1 1 M-l ( a,/''" ?'p zindelO Lc- 'LI v» WAHLUKE . 71 1 1 « vlATILLA MOTTINC golden iJP* 1 i 1 1 or KENNEWICK -"'•:. ;er D RAIN ©. ^n (MONROE o 1 ' | f» DALLES VAr ICC uv .R ^ •^PORTLAND NEWPORTS /tf 20 30 40 50 Average Ar?/7i/a/ ffo/r>fo//, /s?c/?es. eo 70 Fig. 158. — Variation of Rainfall with Altitude in Certain Valleys in North- western United States (see page 285). rainfall with altitude and is for an area near the coast, and it should be noted that the slope of these lines increases and the rate of rainfall increase continually gets less and less as the river valleys considered are farther inland and the moisture content is reduced by precipita- tion. This tendency is exhibited by all the diagrams and shows uni- formly greater rates of rainfall increase with altitude in those valleys General Considerations. 287 situated so that they receive air of greater absolute humidity. Another point to be noted is that the more broken and irregular the topography, the greater is the difficulty of determining any fixed relation between altitude and rainfall; this is shown on the diagram by the greater scattering of the plotted points. This probably is due entirely to the effect of the various topographic features in influencing the direction and moisture content of the prevailing winds. 3 <0 A7ot//?r Wasfr/r?// 5faf/ons % » A7f. Wosntnqfon -£/. 6Z93 ft., &k: tfnn. ea/nra// 85.53 Inches. Fig. 160. — Average Rainfall of the New England States Showing Relation, to Altitude and Geographical Location (see page 290). General Considerations. 289 ington. The map of this region (Fig. 160, page 288) will apparently show a somewhat constant increase of rainfall toward the summit of the mountain. If, however, we examine Fig. 159, we find that of the sixteen stations shown on the map between Mount Washington and the seas, all are below elevation 800 feet, and that Mount Washington has an elevation of about 6,200 feet. The annual rainfall of the sta- tion near sea level varies from about 35 to 46 inches and averages about 41 inches, while the average annual rainfall of Mount Wash- ington is over 85 inches. With such an indefinite starting point and no stations between 800 and 6,200 feet, the direction of the gradient of rainfall intensity is not well established, and the dotted lines indi- cate gradients which may possibly obtain. It is evident that for sta- tions between 2,000 feet and 5,500 feet, estimates of average annual rainfall may vary 10 to 25 inches or more from the truth, and that such estimates can not be made with any great degree of accuracy. 138. Factors Affecting Amount of Precipitation. — It has been shown that the intensity of rainfall is influenced by location rela- tive to (a) sources of moisture and direction of normal winds, (b) paths of cyclonic storms, and (c) the topographical relief of the country. Mountainous countries by causing an upward flow of moist atmospheric currents produce expansion, dynamic cooling and conse- quent precipitation. Topographical relief is only one element in the problem ; before precipitation will occur there must also be moist at- mospheric currents, moving in such a direction that they will rise and expand sufficiently to produce relative humidities at and below the dew point." The presence of moisture is more essential to precipitation than high altitudes. For example, the Pacific Coast Range of the United States, with an elevation of about 3,000 feet, induces a precipitation of 60 inches or more from the currents of moist air from the Pacific Ocean, while the higher altitudes of the Sierras (9,000 to 11,000 feet) induce a materially less rainfall from the air currents which have been con- siderably reduced in their absolute humidity (see Fig. 91, page 170). While the general drift of the atmosphere in the United States is east- erly, it has also been shown that in general the local air currents are toward the centers of low pressure, and continually vary with the prog- ress of the storm center. Thus in turn each source of moisture in or adjacent to the continent is induced to contribute more or less vapor to the atmosphere and to the precipitation induced by the passage of storms. Hydrology — 19 290 Rainfall and Altitude. The study of almost any rainfall map will show many anomalies which cannot be satisfactorily explained. The paths of storm centers while approximately constant vary from year to year and from storm to storm. The intensities of the centers vary and the directions of the consequent incoming air currents are subject to many contingencies that are entirely fortuitous so far as human understanding is concerned. The consequent rainfalls are never the same for any two storms and still less similar for any combination of storms. This will be clearly ap- preciated from a study of the annual rainfall maps of Wisconsin (pages 205 to 206) an area in which the topographical relief is so small as to have little or no influence on precipitation. In the same manner that the varying storm intensity and movement combine with the sources of moisture and geographical location to produce changes in the distribution of precipitation, so the same factors combine with altitude to produce varying conditions at elevated stations and as the topographical conditions at high altitudes are more irregular, the irreg- ularity of rainfall distribution due to altitude is more pronounced. The mean annual rainfall map of New England (see Fig. 160, page 288) illustrates the influences of altitude, topography and geo- graphical location. From the coast the rainfall gradually increases as the White Mountains are approached and reaches a maximum of 85.53 inches at the station on the top of Mount Washington. To the west of the White Mountains, there is a material decrease in rainfall probably due to distance from the ocean and the low intervening ele- vation. The rainfall is increased somewhat by the altitude of the Green Mountains of Vermont, but no data are available as to the maxi- mum precipitation on their summits. That such an increase is pos- sible is evident, but it is not sufficiently assured to warrant any con- siderable investment based on such an increase. In the State of Maine the precipitation seems to decrease almost di- rectly with the distance from the ocean, but westward from the coast of Massachusetts and Rhode Island there is an increase in rainfall as the distance from the ocean increases that cannot be attributed, except in a minor degree, to the effect of altitude. To the southwest, the altitude of the Catskill Mountains undoubt- edly induces increased precipitation (see Fig. 161, page 291) and yet the irregularity of the relations of altitude and intensity on the differ- ent portions of the mountains seems to be greater than would normally be accounted for by distance from the sea, and illustrates the inade- quacy of our knowledge as a basis for estimating such relations with- out extensive precipitation data. Southern California. 29 139. Southern California. — The effect of altitude on rainfall inten- sity often becomes more obvious in arid countries and is frequently of much greater importance in local engineering problems. Southern California while bordered by the Pacific Ocean is far from the normal VCQMOMT AfaS5/JC/iU5fTT5 lln C 2000 ! COA/A/£CT/CUT Fig. 161. — Average Annual Rainfall in the Region of the Catskill Mountains (see page 290). 292 Rainfall and Altitude. paths of storm centers. The normal annual rainfall of the level coun- try is therefore low and the importance of conserving the flow of streams for water supply and irrigation is very great. San Diego lo- cated close to the ocean has an average annual rainfall of 9.62 inches, while at Salton, about 80 miles from the coast, behind the Coast Range and about 260 feet below sea level, the average annual rainfall is about three inches. In the mountains to the eastward and near the Coast, the rainfall is greatly increased and such increase must be considered 6000 5000 4000 / J \y Ne///e 1 1 1 # y Cuij-amaca Pes. 4 Y ' a Ju//an ( uchman 5pr/r?q S 70 Dam^^s.b \ »I_ ■ Warners S t vr/nq Morei a Mesa Grande l/T X^Tl^o^i 1 / Ca vipo "M? ■ P \^ oanra rsai we t dan -etf Dam . 2 E/smore . ? Va//eu 1 y^\ Center fa// BrooA w f Jama/ i ' Escoi id/da y J? 1 j> v^owol, Sweetwafer Do m 5o//on t ea 5an O/eao .5 3000 ^ zooo \ /ooo O 4 8 12 /6 20 24 28 3Z 36 40 44 48 Ga/nfa/J in Inches Fig. 162. — Altitude-Rainfall Diagram for San Diego and Vicinity. in various engineering problems. 1 Considerable rainfall data are avail- able in this region and approximate isoheytal lines may be constructed which will serve more or less as a g"uide in such estimates. It is found, however (see Fig. 162), that altitude alone is not a safe guide to amount of rainfall for while as a general rule for this region average annual amount increases with altitude, this increase may be from .4 inch or less per 100 feet to .8 inch or more per 100 feet of rise. These ratios represent differences in local precipitation much greater than would at first appear for it should be noted that at Warner's Springs (elevation 3,165) there is an average annual rainfall of 16 inches, while at Mesa Grand (elevation 3,300) there is an average annual rainfall of 30.70 inches. Note also the increase in rainfall from Escondido (el. 657) to Warner Springs (el. 3165) is only 0.93 inches, 1 Construction of the Morena Dam, San Diego County, California, by M. M. O'Shaughnessy. Trans. Am. Soc. C. E., "Vol. 75, page 27. Southern California. !93 while the comparison of the rainfall of Valley Center (el. 1365) with Warner Springs shows a decrease in average annual rainfall of nearly 4 inches with a rise of 1800 feet. Fig. 163. — Topographic Map of San Diego and Vicinity Showing Relative Locations of Rainfall Stations. In making estimates of the rainfall at intermediate stations within this area, great care is therefore needed to secure results which are even approximately correct. The mean annual rainfall (1910) at various stations in San Diego County and vicinity is given in Table 31, together with the elevation 294 Rainfall and Altitude. of the station. 2 A topographical map, based on the maps of the U. S. Geological Survey, showing the relative locations of rainfall stations is shown in Fig. 163. On this map all areas lying above elevation 2,000 feet are cross hatched. TABLE 31. Rainfall Stations, San Diego County, California, and Vicinity. Length of Elevation Average observation above sea level annual rainfall Period, years Feet Inches Nellie 7 5,300 44.26 Cuyamaca Reservoir 21 4,677 38.84 Julian 28 4,250 26.36 Noble's Mine 3 4,200 24.5 Buckman Springs 2 3,500 19.90 Mesa Grande 5 3,300 30.70 Morena Dam 5 3,300 24.15 Warner's Springs 4 3,165 16.08 Santa Ysabel 10 2,983 24.17 Campo 31 2,189 19.98 Barrett Dam 5 1,600 19.07 Valley Center 26 1,365 20.03 Elsinore 12 1,234 13.64 Jamul 6 900 13.00 Fallbrook 27 700 17.14 Escondido 14 657 15.15 El Cajon 10 482 12.24 Foway 29 460 13.79 Sweetwater Dam 20 238 9.52 San Diego 53 87 9.62 Salton Sea 30 —260 3. TABLE 32. Rainfall Stations in Southern Arizona and New Mexico. Length of Station observation period, years Luna, N. M 14 Rosedale, N. M 11 Flagstaff, Ariz 22 Bluewater, N. M 14 Ft. Bayard, N. M 46 Pinto, Ariz 10 Snowflake, Ariz 12 Lake Valley, N. M 10 Ft. Buchanan, Ariz 4 Bisbee, Ariz 25 Prescott, Ariz 48 Ft. Apache, Ariz 41 Ft. Huachuca, Ariz 30 Holbrook, Ariz 24 2 Tbid, page 54. Altitude Average above sea annual rainfall level, feet inches 7,300 15.94 6,900 19.26 6,907 22.96 6,732 9.53 6,152 15.42 5,660 11.49 5,644 10.27 5,413 14.71 5,330 21.58 5,350 18.44 5,320 17.21 5.200 17.87 5,100 17.06 5,069 9.30 Rainfall Stations, Arizona and New Mexico. 295 TABLE 32— Continued. Rainfall Stations in Southern Arizona and New Mexico. Length of Altitude Average Station observations above sea annual rainfall, period, years level, feet inches Ft. Grant (Bonita) Ariz 39 4,916 14.27 Alma, N. M 18 4,800 15.65 Jerome, Ariz 17 4,743 18.92 Tombstone, Ariz 17 4,550 13.85 Pinal, Ariz 23 4,520 23.45 Oracle, Ariz 19 4,502 19.50 Gage, N. M 16 4,420 10 21 Mimbres, N. M 4,339 18-42 Deming, N. M 39 4,333 10.03 Tonto, Ariz 13 4,300 15.15 Cochise, Ariz 25 4,250 11.69 Lordsburg, N. M 26 4,245 9.36 Wilcox, Ariz 35 4,203 10.91 Gila, N. M 8 4,040 14.50 Douglas, Ariz 20 3,930 15.03 Nogales, Ariz 17 3,830 13.97 Breckinridge, Ariz 6 3,800 17.03 Bowie, Ariz 35 3,756 14.10 Globe, Ariz 15 3,625 16.71 San Simon 25 3,609 7.86 Clifton, Ariz 25 3,584 13.55 Benson, Ariz 34 3,523 9.47 Kingman, Ariz 13 3,326 11.02 Vail, Ariz 26 3,241 10.69 Verde, Ariz 22 3,160 13.13 Ft. Thomas, Ariz 26 2,816 11.46 Thatcher, Ariz 17 2,800 10.23 Rice, Ariz 33 2,540 11.30 San Carlos, Ariz 25 2,456 12.91 Tucson, Ariz 49 2,400 11.74 Cline, Ariz. . . : 14 2,300 15.49 Dudleyville, Ariz 23 2,204 14.59 Wickenberg, Ariz 14 2,072 9.47 Redrock, Ariz 12 1,864 11.18 Florence, Ariz 18 1,493 9.88 Casa Grande, Ariz 26 1,396 5.76 McDowell, Ariz 23 1,250 10.38 Mesa, Ariz '. . 19 1,244 8.78 Maricopa, Ariz. 36 1,180 6.19 Phoenix, Ariz 24 1,100 8.00 Buckeye, Ariz 24 980 7.34 Sentinel, Ariz 16 685 4.00 Gila Bend, Ariz 25 787 5.82 Mohawk, Ariz 28 538 3.32 Aztec, Ariz 9 492 3.92 Parker, Ariz 19 353 4.82 Yuma, Ariz 35 140 3.00 140. Southern Arizona. — The relation of altitude to mean annual rainfall intensity in Southern Arizona is shown by Fig. 164, page 296. The solid inclined lines on this figure indicate rates of increase of 296 Rainfall and Altitude, rainfall with altitude, while the dashed lines show rules or formulas suggested for this region. The approximate topographical conditions surrounding the various stations are shown in Fig. 165, page 297, in l< 5000 % 3000 2000 / ' / A/ / / LUMA ■ F f /~ / / TAFF' Lo°/U Arosedale Abluew ATER V 1 /fV -V /o / // (#/ // AFT BAYARD ^ M -^ 1 1 SMOWFUAKEA AP NTO Oy s? / i .LAKE VALLEY b r , - ~t5 /! ' !pRESCOTT« | | • BISBEE- • FT BUCHANAN 1 Aholbrook FT HUACHUCA- ""■^ r/ i <: ■/ / ' FT GRAN p^n /,, B \$A- 1 / J- V • JEROME M E P V"' •OF ACLE PINAL* ORD Adem BURG A T NG ' «C OCHISE •TONTO JT1IMBF E5« rf A GILA*/ ' y /A^ /, 7_.D ? UC LA 5 hojr- SAN // // ^ • SOW -IFTO / 'V LOBE / o*y 1 Abe NSON j /• > / ixy • kingman •VAIL 1 / - ^ */- / ..«S. J^ / / / 1/ X «!# x" 'THA rcHEF / / rr /I / THOflAS- / 1 / VER 3E._L / ^ 5/^ _z • SIL / RICE • / -tucso'n— / .•BAN CARLO s / DUDLEYVIL '" 1 - /»CL INE / V VICKE NBER / / / ^ 7a / • RSDROCK r / $ /A CASA GRAf> / / / 'FLORENCE « / 1 / «p lESAJ-^MCDOWE LL / J 7 f 1 /Yempe PHOENIX / ' zU A SENTINE / T / L 'GILA BEND /az' HAWK / / lZ. /"PARK :r Sror/or?^ r shown A are beyond the D/vide. r T ^ /a /s /a A verage Annc/a/ rla/hfa//. //defies. Fig. 164. — Altitude-Rainfall Diagram for Southern Arizona (see page 295). which the areas lying above elevations of 5,000 feet are shown cross batched. In Arizona as in Southern California the general increase of intensity with altitude is at once apparent from Fig. 164; but a brief examination of the data will indicate the great danger of error in any estimate of the average intensity of the annual rainfall for inter- Southern Arizona. 297 ~ r '"y T ^"W~^T 298 Rainfall and Altitude. mediate stations. The great range in the average amount of annual rainfall at various stations beween 4,000 and 5,000 feet in altitude should be noted. Table 32 gives the rainfall stations in the area to- gether with the period of observation, altitude above sea level and mean annual rainfall of each station. Several attempts have been 8000 1000 ^6000 5 5000 • Soldiers Summit Oakley « Woodruff •A) Cas I i i • 7/e Go 1 3 vr Creek • vnm /s/d *3c /pio «lienefer 1 1 Th/sf/e • i j • Promontory f Too ?/e */P/p/ne i f'/berta 1 'bo • Deseref I Provo 1 • Logan ( ~orr /ne Oqden » 3oi / lake Farn iinqfor? • 1 1 1 7 8 9 /O // 12 /3 14 15 /6 17 18 19 20 21 22 Average tfnnuo/ £?ainfo// in Inches Fig. 166. — Altitude-Rainfall Diagram for Southern Utah. made to establish definite rules for calculating these relations for parts of this territory, which are discussed in Section 143. 141. North Eastern Utah. — The distinct increase of average annual rainfall with altitude is not always as definite as in the cases discussed in Sections 139 and 140. In northeastern Utah west of the Wasatch Mountains, the Great Salt Lake seems to have an influence on the rainfall of the stations to the east which almost entirely obscures the effect of altitude. Here a few miles distance from the lake seems to have a much greater effect than a considerable difference in altitude. These relations are shown in Fig. 166, and the approximate topographi- cal conditions are shown in Fig. 167 in which the cross hatched por- Northeastern Utah. 299 Fig. 167. — Topographic Map of Northeastern Utah. 300 Rainfall and Altitude. tion indicate elevations above 7,000 feet. The effects of Great Salt Lake are further emphasized by the low precipitation at stations south of the lake and away from the ordinary paths of atmospheric move- ment over this body of water. The influences of locations beyond the divide are also obvious. It should also be noted that a line passing TABLE 33. Rainfall Stations in Utah. Length of Elevation Average observations above sea annual rainfall, Station period, years level, feet inches Soldiers Summit 12 7,425 12.10 Oakley 4 6,750 21.2 Woodruff 4 6,500 10.01 Meadowville 14 6,200 17.41 Heber 22 5,620 17.46 Manti 20 5,575 12.10 Theodore 3 5,507 9.92 Castledale 16 5,500 8.63 Henefer 15 5,301 19.30 Sunnyside 5 5,282 14.86 Govt. Creek 14 5,277 13.44 Scipio 20 5,260 15.22 Thistle 21 5,075 14.76 Levan 19 5,010 16.38 Promontory 30 4,913 8.23 Alpine 8 4,900 19.28 Tooele 19 4,900 15.93 Elberta 13 4,650 10.06 Mt. Nebo 8 4,650 10.53 Deseret 20 4,541 7.88 Provo 21 4,532 14.20 Logan 24 4,507 15.97 Salt Lake 41 4,366 16.03 Ogden 44 4,310 14.55 Parmington 10 4,267 21.17 Corrinne 45 4,240 12.51 Saltair 11 4,220 15.15 near Saltair, Heber and Oakley, seems to indicate a certain approxi- mate relation of altitude to rainfall intensity in one direction, conclu- sions from which would be quite different from those which would be drawn from a similar line drawn near Saltair, Provo, Thistle and Sol- dier's Summit. It should also be noted that the difference in rainfall between Salt Lake City and Alpine or Farmington cannot reason- ably be attributed to distance from the lake or difference in altitude but must be due to the local direction of moist air currents not to be accounted for without much fuller information than is here available. Table 33 gives the rainfall stations in this area together with the period Relations During Single Storms. 30 of observation, altitude above sea level, and the mean annual rainfall of each station. 142. The Relations of Altitude and Rainfall During Single Storms. — The relation of average annual rainfall to altitude is modi- fied by the many fortuitous circumstances which surround the occur- rence of the numerous local and general rainstorms of which these an- nual means are made up. A study of single storms may give a more 5000 3000 S EOOO /ooo eo /so /so eoo 2^0 D/sfa-rrce fKorrt Secrcoasf, A7//es. 300 Fig. 168. — Topographic and Rainfall Profiles for the Storm of July 14-17, 1916, in the Carolinas (see page 302). distinct idea of the influences of various factors on the main problem. The great storm which occurred in the South Atlantic and East Gulf States, July 14 to 17, 1916, has been briefly discussed (see Section 85) and illustrated (see Figs. 95 and 96, pages 174 and 175). As is ordinarily the case with rainstorms which accompany West Indian hurricanes, a considerable rainfall occurred close to the point at which the hurricane path first encountered the land. In most cases the rainfall of the interior rapidly decreases as the distance from the Coast increases. In this case, however, the hurricane moved di- rectly toward the southeastern spur of the Alleghenies and was ap- parently dissipated thereby. The altitudes encountered induced a still heavier rainfall on the mountain slope and a record precipitation 302 Rainfall and Altitude. on or near the summit. Fig. 168 shows the profile of the land surface on a line from near Georgetown, S. C. to Altapass, N. C. On this profile is also shown the location and comparative elevation of various stations on or adjoining the line of this profile, and above each is platted the depth of rainfall that occurred during his storm. This Pig. 169. — Topographic and Rainfall Map of the Los Angeles District (see page 303). profile shows the great rainfall which occurred closely adjacent to the Coast and the greater rainfall on the mountains. A heavy rainfall was apparently also induced in the region just beyond the divide, and the radical decrease in precipitation at Elizabethtown about 30 miles farther on is also shown. An unusually heavy rainstorm occurred in the Los Angeles district in Southern California, Feb. 18 to 21, 1914. This rainfall was oc- casioned by a storm the center of which slowly approached the north- ern Pacific Coast, passed over Port Crescent Feb. 22, and was appar- Relations During Single Storms. 303 -ently dissipated in the mountains. Its slow movement gave rise to far reaching effects, as is shown by the unusual precipitation in South- ern California. Fig. 169 is a topographical map of the Los Angeles region on which have been drawn isohyetals 3 which indicate in a gen- eral way the effect of elevation on the rainfall intensity. Distance from the sea here seems to have little effect, the apparent factors being 6000 / % W, 1 7sor?V^o 5000 ' ! i \ 4000 <0 1 N t \ 3000 1 v ^ < X \J 2000 ^^ 1 ffa/'r? eg// ^ proj ilS^\ /ooo f Groc/r?a' f 3 /- of/fes Y /nd/cates e/ev of s/of/on \ » 1 -a/nfa //af 4 8 /£ 16 20 24 28 32 D/stortce frorr? Seercoosr, A7//&S Fig. 170. — Topographic and Rainfall Profiles for the Los Angeles District. the direction of the air currents and altitude. Fig. 170 shows a profile of surface elevations and of rainfall intensities based on the records of stations closely adjoining a line drawn from San Pedro to Mount Wil- son. Table 34 gives the rainfall stations in this area together with the period of observation and altitude above sea level at each station. It is pertinent and instructive to add that the relations of altitude to intensity of precipitation as indicated by the records at Los Angeles and Mount Lowe are not alone indicated by individual rain storms but are also clearly shown by the average monthly and annual precipita- tion at these two stations as shown graphically by Fig. 171. 4 It is to be noted, however, that the rainfall for each individual storm or for 3 Flood Studies at Los Angeles, F. A. Carpenter. Monthly Weather Review, .1914, page 385. 4 Ibid, page 385. 304 Rainfall and Altitude. TABLE 34. Rainfall at Stations Near Los Angeles Cal, Station Elevation, Jan. 12-19, Jan. 22-29, Feb. 18-21. feet 1916 1916 1914 inches inches inches 30 3.45 540 12.30 4.56 13.26 4,600 10.83 714 4.81 1,200 10.80 4.74 10.92 4,537 17.85 615 8.28 6.16 4.31 8.63 1,334 4.85 470 6.44 536 9.41 1,316 5.68 400 6.75 47 3.24 293 6.90 3.49 7.07 2,950 7.36 6.16 11.10 3,500 11.40 3.76 19.20 5,850 13.40 5.90 19.40 176 3.55 584 3.90 1,100 3.87 827 8.82 3.49 11.44 857 10.50 4.92 9.60 1,352 5.84 3.33 4.26 16 3.51 851 4.80 3.53 2.79 1,888 12.25 1,066 8.47 3.55 8.88 1,054 8.75 4.57 4.71 909 11.29 19 3.00 2.60 2.03 110 7.14 4.13 5.50 1,400 10.21 4.27 15.56 5,280 27.78 • 10.86 16.29 125 4.01 3.83 3.52 3,750 5.16 0.58 5.57 25 5.16 50 10.21 600 6.96 246 5.02 Avalon Azusa Bear Valley Dam.. Chino Claremont Cleghorn Canyon . . Corona Devil Canyon East Highlands . . . Fillmore Garvanza* Highland Hollywood* Long Beach Los Angeles Mill Creek Mt. Lowe Mt. Wilson Orange Palm Springs Palos Verde Pasadena Pomona Redlands Redondo Riverside San Antonio Canyon Pacoima San Bernardino . . . San Dimas San Pedro Santa Monica Sierra Madre Squirrel Inn Tustin Valyermo Venice Ventura Walnut Whittier * Suburb of Los Angeles. each individual month or year does not uniformly show such relations. (See Table 35.) 143. Rules for Estimating Relations of Altitude to Rainfall.— While it has been possible to discuss in this chapter the relation of alti- tude to rainfall in only a few local districts, enough has been said and shown to emphasize the fact that any rule for estimating such relations Estimating Relations. 305 TABLE 35 Comparison of rainfall of Los Angeles and Alt. Lowe Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec 1896 Los Angeles Mt. Lowe... 3.i3 2.85 T 0.10 2.97 4.10 0.19 0.60 0.30 0.30 T 0.00 0.02 0.00 0.01 0.10 T 0.00 1.30 2.39 1.66 1.55 2 12 2.17 11.80 14.16 1897 Los Angeles Mt. Lowe . . 3.70 6.42 5.62 7.47 2.31 6.67 0.02 0.19 0.10 0.87 T 0.10 T 0.15 0.00 0.00 0.00 0.00 2.47 2.57 0.01 0.40 0.05 0.22 14.28 25.06 1898 Los Angeles Mt. Lowe .. 1.26 1.55 0.51 2.22 0.98 1.65 0.03 2.70 1.75 2.17 T 0.00 07 0.00 T 0.00 0.02 0.25 0.09 0.30 T 0.90 0.12 0.98 4.83 11.82 1899 Los Angeles Mt. Lowe .. 2.64 3.29 0.04 0.00 1.81 3.40 0.18 0.20 0.04 1.90 0.58 0.40 0.00 0.00 0.01 0.00 T 0.00 1.59 3.00 0.90 2.85 0.90 2.14 8.69 17.18 1900 Los Angeles Mt. Lowe . . 1.17 5.50 T 5.03 0.99 2.90 0.54 2.15 1.81 4.05 T 0.40 T T T 0.00 T 0.25 0.26 1.66 6.53 11.71 T 0.00 11.30 33.65 1901 Los Angeles Mt. Lowe . . 2.49 7.55 4.38 5.42 0.45 1.18 0.68 1.14 1.50 4.45 T 0.75 T 0.00 9.69 0.00 03 0.00 1.88 4.18 0.46 1.05 0.00 0.23 11.96 25.95 1902 Los Angeles Mt. Lowe . . 1.62 1.88 3.35 3.48 3.98 5.97 0.16 1.35 0.03 0.33 T 0.30 T 0.00 T 0.00 T 0.00 0.40 0.90 2.08 3.68 2.50 2.14 13.12 20.03 1903 Los Angeles Mt. Lowe 2.10 1.52 6.93 3.77 T 0.02 0.00 T 0.43 T 0.00 T 14.77 1904 Los Angeles Mt. Lowe . . 0.14 0.00 2.68 4.02 4.50 6.92 0.97 2.10 T 0.20 T 0,00 T 0.00 0.17 1.27 0.28 1.50 0.69 0.00 0.00 0.00 2.45 1.98 11.88 17.99 1905 Los Angeles Mt. Lowe .. 2.57 4.02 6.06 12.53 6.00 10.56 0.35 1.07 0.95 4.01 0.00 0.00 0.00 0.00 0.00 0.00 T 0.00 0.08 0.24 2.98 3.74 0.20 0.12 19.19 36.29 1906 Los Angeles Mt. Lowe . . 3.85 4.55 2.47 3.80 7.35 18.66 0.69 2.28 1.02 3.50 0.01 0.00 0.02 0.00 0.03 0.22 0.05 0.00 0.00 0.00 0.85 1.04 5.12 11.85 21.46 41.90 1907 Los Angeles Mt. Lowe .. 7.02 12.83 1.83 3.60 4.12 7.24 0.16 1.90 0.07 0.89 0.03 0.94 0.00 0.00 0.00 0.00 T 0.00 1.18 3.36 T 0.05 0.88 1.67 15.30 32.48 1908 Los Angeles Mt. Lowe .. 5.04 6.84 3.66 5.56 0.18 1.02 0.52 1.90 0.25 0.95 0.00 0.00 T 0.00 0.08 0.00 1.22 2.48 0.25 0.80 1.08 0.75 1.46 2.13 13.74 22.43 1909 Los Angeles Mt. Lowe .. 7.27 14.22 5.20 11.94 2.51 7.38 T 0.56 0.00 0.03 0.11 0.75 0.00 T T 1 0.02 0.04 0.15 0.28 1.40 1.51 3.10 7.00 18.98 23.92 251.53 1910 Los Angeles Mt . Lowe . . 1.53 1.40 0.11 O.U 1.86 3.80 0.30 0.27 0.00 0.02 0.00 0.00 0.04 T T 0.0 0.01 0.00 0.82 1.05 0.15 1.57 0.07 l 0.07 4.89 3 8.32 1911 Los Angeles Mt. Lowe . . 6.70 15.76 2.91 4.37 5.15 5.95 0.28 1.90 0.02 0.25 0.03 0.00 T 0.00 O.fO 0.00 1.23 2.00 0.16 0.20 0.1U 0.22 1.27 1.25 17.85 31.90 1912 Los Angeles Mt. Lowe . . 07 0.5U 0.00 O.iO 6.99 8.12 1.66 2.67 0.12 0.87 0.00 0.(0 T 0.00 0.00 0.00 0.0' 0.00 0.56 2.20 0.35 0.60 0.03 T 9.78 14.96 1913 Los Angeles Mt. Lowe . . 2.01 3.16 9.16 11.60 0.33 0.76 0.35 0.98 0.05 T 0.58 1.65 T 0.05 T 0.03 0.03 0.05 T T 3.00 4.00 1.66 2.85 17.17 25.10 1914 Los Angeles Mt. Lowe .. 10.35 12.70 7.04 19. 2J 0.58 1.30 0.47 2.12 0.43 0.98 0.09 0.20 0.01 T 0.00 0.0 J 0.00 0.00 0.31 1.43 0.20 T 3.73 5.80 23.21 43.73 1915 Los Angeles Mt. Lowe . . 5.42 8.60 5.09 8. 00 0.60 1.22 0.81 2.44 0.88 2.45 T o.co 0.00 0.00 0.00 0.00 T 0.10 0.00 0.00 1.35 2.00 2.52 2.70 16.67 27.51 1916 Los Angeles Mt. Lowe 13.30 19.86 1.82 2.87 0.90 4.15 T 0.00 0.03 0.00 0.00 0.00 0.00 0.00 T 0.00 0.77 1.80 2.71 5.00 0.09 0.30 3.67 6.40 23.29 40.38 i Estimated 2 Includes estimated a Includes estimated total for August total for Decern ber Hydrology — 20 306 Rainfall and Altitude. must be purely local. Even in these cases rules must be regarded as subject to possible exceptions which may greatly affect the accuracy of estimates based thereon. The very statement of the attempted rule often shows the difficulties in its application. On the north slope of the French Alps, at the elevation of 1,5(30 me- Mar. Apr. May /"> r\ 1 n \ WW Low / " \ Los Anoe/esfr- — _,_ --' 1 I \s- O. ^ •'' Jan Feb Mor Apr.Moy Jun Jut Aoa. Sept Oct A/ov. Dec Fig. 171. — Average Rainfall at Los Angeles and Mt. Lowe (see page 303). ters, an average rainfall of 1,500mm has been observed; and it is as- sumed that as a general average, the rainfall in the regions above 1,500 meters increases by 150 to 250 mm for every 100 meters eleva- tion. Certain small regions may, of course, have results that differ from this arbitrary rule. 5 In Austria the plains have the least rainfall. In Central Bohemia and in Mahren and Lower Austria, etc., the yearly rainfall decreases to 200 to 300 mm. The following table, compiled by Bebber, shows the effect of elevation upon rainfall : 6 From 100- 200 m. above sea level 583 mm 200- 300 650 300- 400 696 400- 500 782 500- 700 852 700-1,000 995 1,000-1,200 1,308 5 Der Wasserbau, 1907, Th. Koehn. « Frederick Kulturtechnischen Wasserbau. Estimating Relations. 307 Usually attempts to formulate the relation of rainfall to altitude haA^e been expressed by a straight line equation : 7 A R' = R + K 100 in which R' and R are average annual rainfalls at the higher and lower points respectively, A is the difference in altitude in feet, and K is a constant for the region. Values of K range from two-tenths to eight- tenths of an inch in the West, six-tenths being frequently used for the Sierras of California. A value of 0.21 was derived by Mr. J. B. Lip- pincott for the Gila and Salt River Basins in Arizona. 8 The rule which was formulated by Lippincott about 1899 still seems in the light of seventeen years additional data to apply with reasonable accuracy to the local conditions in this valley. It should be used, however, only after careful consideration of the local condition of the area for which an estimate is to be made. Prof. G. E. P. Smith has sought to establish such relations for certain areas in Southern Arizona. 8 He has suggested two curves, one for Cochise and Graham Counties, and the other for Pima and Pinal Coun- ties. The author has been unable to ascertain any adequate reason for the differentiation between these Counties, or for the belief that there is any increase in annual rainfall above the 4000 foot contour. 144. General Conclusions. — While in general rainfall will increase with altitude, it is dangerous to assume that this will always be the case, as there are many exceptions to this rule. Where the rule holds, the amount of such increase is difficult and often impossible to determine. An assumption of large runoff for mountain streams based solely upon elevation where no records of mountain rainfall or runoff are available, is unsafe and does not warrant large investments in projects based upon such assumptions. LITERATURE. The Relation of Rainfall to Mountains, W. H. Alexander. Monthly Weather Review, 1901, p. 6. Relation of Rainfall to Runoff in California, J. B. Lippincott and S. G. Bennett. Eng. News, Vol. 47, 1902, p. 467. " Rainfall and Surface Waters, G. E. P. Smith. Bui. 64, Arizona Agricul- s Bulletin 64, Arizona Agricultural Experiment Station. tural Experiment Station. s Ground Water Supply and Irrigation in Rillito Valley, G. E. P. Smith. Univ. Arizona Agric. Exp. Sta., Bui. 64, 1910. 308 Rainfall and Altitude. The ^TJieory of the Formation of Precipitation on Mountain Slopes. Prof. E. Pockels. Monthly Weather Review, 1901, p. 152 See also "Mechanics of the Earth's Atmosphere," Smithsonian Miscella- neous Collection, Vol. 51, No. 4, Article VIII. Effects of Mountains on Humidity, Cloudiness and Precipitation, Dr. Julius Hann. Handbook of Climatology, translated by R. De C. Ward. The MacMillan Co., 1903. Rainfall in England in Relation to Altitude, W. Marriott. Quar. Jour. Royal Met. Soc, Vol. 26, 1900, p. 273. Precipitation and Altitude in the Sierras, Chas. H. Lee. Mon. Weath. Rev., July, 1911, p. 1092. Ground Water Supply and Irrigation in Rillito Valley, G. E. P. Smith. Univ. Ariz. Agric. Exp. Sta., Bui. 64, 1910. CHAPTER XIII GEOLOGICAL AGENCIES AND THEIR WORK 145. Hydrological Influence of Topography and Geology. — The geology of a district and its accompanying topographical and strati- graphical conditions greatly modify its hydrological phenomena. Sharp topographical relief, as shown in Chapter XII, exerts a notable influ- ence, quantitatively uncertain, by increasing precipitation on the wind- ward side and decreasing precipitation on the leeward side of consider- able elevations. The character of the material and the dip of the strata have had a marked influence on the trend of the development of streams, and still have such influence on the effect of the flow on the denudation of the exposed strata. The structure, extent of outcrop and slope of the strata have an im- portant effect on the disposal of rain waters and greatly modify the rela- tive amounts of evaporation, absorption and surface flow. These same factors, together with the amount and distribution of the precipitation received on the exposed outcrops of the strata, are the controlling ele- ments which modify the presence and flow of underground waters. The surface slope of the country and the character of the rocks com- posing the drainage area, together with the amount and distribution of the precipitation, are controlling factors in the character of runoff or stream flow. All of these factors are in turn modified by geographical and climatic conditions. A study of local geological history gives in- dications of the possible or probable character and extent of the under- lying strata and is prerequisite to intelligent local investigations. The present conditions have been brought about through agencies that are still active and which are still impressing their influence on the earth's surface. While the activity of these agencies may have been modified by changes in climatic and other conditions, the general nature of their action remains unchanged and a study of their past effect will give an intelligent basis for the type of construction necessary to utilize these agencies for the benefit of mankind. For a proper knowledge of the hydrological conditions of any district, an understanding of historical and general geology and of the character of the agencies and sequence of events that led up to the local geological conditions that now obtain, is frequently indispensable. 310 Geological Agencies. In a general treatise on hydrology it is possible to discuss geology in a very general way only, and to consider in greater detail but still in a most general way, a few of the most important factors and conditions which influence or control the problems of the hydraulic engineer. The knowledge of general geology necessary for a clear conception of many problems in engineering, as well as the detailed study of the more or less local conditions which for successful results must be investigated and understood, can be secured by the engineer from the many special treatises on these subjects. 146. Outline of Causes Productive of Topographical and Geo- logical Changes. — The following is a summary of the agencies that have been active causes of the evolution of the earth's surface from past to present structure and form. These agencies are still active and operative, and an appreciation and knowledge of them are essential in order that the engineer may design his structures for stability and per- manency so far as possible. A. Factors of Disintegration: (a) Rock Texture: Resistant — Capable of withstanding erosive agencies for considerable periods. Yielding — Easily eroded. (b) Vegetation : Wedging action of plant roots. Decay of vegetation re- sults in the formation of acids which increase solvent power of water. Retards surface erosion of soil where thick enough to form a protective covering. B. Factors of Erosion, Corrosion and Transportation: (a) Crust Movements: Unequal settlements resulting in oceans and continents. Upheavals resulting in islands and mountain ranges. Subsidence. Deep sea inlets, bays, etc. Volcanic. Limited but marked upheavals and subsidence, and ejection of molten matter. (b) Precipitation and Moisture: Concentration of rainfall tends to increase corrasion and transportation powers by increasing volume and ve- locity of runoff. Plumidity of atmosphere tends to check sudden and con- siderable variations in temperature. Causes of Topographical and Geological Changes. 3 1 1 Rivers : Powers of corrasion, transportation and deposition de- pend on velocity and volume of flow and the material forming the river bed and banks. Ice: Corrasion by glaciers and avalanches. Transportation by river ice. glaciers and avalanches. (c) Ocean and Lake Movements : The waves on the lakes and seas erode the shores against which they impinge. The lake and ocean currents transport the materials eroded by the waves or discharged by the rivers and build up extensions to the land and independent banks in the open water where conditions favorable to depo- sition occur. (d) Atmospheric Movements : Less important than precipitation except in regions of low rainfall. Direct effect great in modifying evaporation and precipi- tation. Shifting of sand dunes. In moist climates dries earth to dust and transports dust and sand. In arid regions there is less rock decay and less vegetation to anchor the products of decay, action of wind erosion in carving rocks (sand blast effect) is often great. Creates waves and currents. 147. Rock Structure and Texture. — The diastrophic movements which have taken place since the indurated formations were first laid down have resulted in the development of joints and fissures in all rock masses at and near the surface which have given greater or less access to the agents of disintegration into exposed rock masses. Rocks of massive structure with few joints and fissures and with small exposures and gentle slopes, and which are protected by mantle coverings, disin- tegrate slowly. On the other hand, bare rocks with open joints and fissures or those composed of alternate beds of hard and soft material having steep slopes or existing as exposed clefts from which loosened material is rapidly removed, are quickly disintegrated. In the same manner the texture of the rock has a considerable influ- ence upon the rapidity of disintegration. If the rock is close grained, 3 1 2 Geological Agencies. impervious, composed of insoluble material and of a physical quality capable of standing erosive action, disintegration is slow. Pervious rocks of loose grain, composed of soluble material which is easily eroded, rapidly yield to disintegration. 148. Erosion. — In order to understand the causes of topographical and geological changes, the extension and reduction of continental areas, the work of waves, tides and currents, the formation, extension and extinction of lakes, the development of drainage systems, the work of rivers and streams, and the consequent changes in the topography of their drainage areas, it is necessary to have a clear understanding of the manner in which the elements combine their actions and the meth- ods b)' which they accomplish their work. There are three principal methods by which the elements of erosion are continually reducing the heights of land toward what is termed the base level, which is approximately sea level, namely : weathering, cor- rasion, and transportation. Weathering is that continual decomposition and disintegration of the rock formations by which they are broken into fragments and reduced to the finest particles. Corrasion embraces the methods by which the action of running water reduces the masses of rocks by abrasion and solution. Transportation is the term applied to the conveyance from their original positions of fragments and particles produced by weathering and corrasion. The rapidity with which the various processes of erosion are carried on depends principally upon the texture of the deposits and on climate, and varies particularly with the abundance of rainfall. 149. Weathering. — The weathering of rocks may be the result of chemical or mechanical processes. Through the agency of chemical action, portions of the cementing materials which bind the rock into a homogeneous mass are dissolved, thus promoting the disintegration of the rock. This action is greatly increased by various impurities which are frequently contained in the water, especially those derived from or- ganic decay. The action of gases in volcanic regions may be classed as a chemical process of weathering. The rapidity with which rocks disintegrate under the chemical processes of weathering depends mainly upon the composition of the rock, the composition and quantity of the water and the temperature. Under the mechanical processes of weathering may be classed the impact of falling rain, the wedging ac- tion occasioned by water freezing within the interstices of the rock, the Weathering. 313 wedging action caused by the roots of plants entering the crevices of the rock, and the variations in temperature, particularly rapid changes in temperature. In regions where the soil covering is derived from the native underlying rocks, the soil is entirely due to the effects of weathering, and the amount of such soil represents the rate at which weathering outdistances the rate of soil removal by transportation. The processes of weathering are largely responsible for the width of stream valleys, for by these agencies the rock is broken up and loosened Tic. 172. — Talus at the Base of Mountains around Moraine Lake, British Co- lumbia. from the sides of the hills and canyons, whence it falls to the stream by which it is broken up and carried away. The deep soil, which is the result of weathering when soil removal has not hitherto been active, is shown by Fig. 9, page 39. Fig. 172, shows the talus at the base of. the mountains surrounding Moraine Lake in British Columbia. This lake is of glacial origin and the talus represents the effects of weathering since the time when the valley was occupied by the glacier. 150. Corrasion. — Corrasion is due in large measure to the abrasive action of material carried in suspension in running waters, and the larger part of this suspended matter is composed of material broken up and loosened by the processes of weathering. When the water of a stream runs over a bed of rock, the destructive effect is dependent itpon the velocity of flow, the depth of flow, the load of detritus it car- 314 Geological Agencies. ries, and the character of the rock ; in other words, the amount of work accomplished depends upon the material worked, the tools used and the energy expended. The principal work is accomplished by the boulders which are rolled along the stream bed (see Fig. 173), and since the size of the boulder moved by a stream varies as *.*■' Fig. 173. — Tools of the Stream, Boulders in the Spokane River. the sixth power of the velocity, the velocity is the important factor in influencing the rate of cutting. That a stream normally swift may be so loaded with detritus that its velocity is materially diminished, may readily be seen when it is considered that it is the bottom velocity and not the average velocity which is effective in cutting, and each ad- dition to its load reduces the energy of the flowing water by the amount necessary to carry the weight along. The maximum rate of corrasion therefore occurs when there is that balance beween velocity and load carried that permits of the most effective abrasive action by the debris upon the stream bed. In those regions where the large part of the yearly precipitation occurs as snowfall, and the summer temperatures are not sufficient to melt all the snow which fell in the previous season,, the greater part of corrasion and transportation is accomplished by the movement of glaciers. 151. Erosion By Wave Action. — The nature of waves and the tre- mendous force of their impact have already been discussed in Sec- Erosion by Wave Action. 315 tions 55 to 60 inclusive. When waves beat against a shore, especially when they are loaded with debris, they may cause considerable erosion,, depending on the nature of the material of the land, the beach struc- ^>^vs^- N :w> x \<<-f- ^^0' v .,r/; Fig. 174. — Coast Erosion by Waves. Fig. 175. — The Illecellewaet Glacier, British Columbia. ture, and the depth of water adjacent to the shore. The normal effect of the waves is both to cut a terrace in the shore line and by means of the receding waters to build up a terrace in the adjacent deep waters. (See Fig. 174). While the material eroded from the shore may furnish effective tools to assist corrasive action of the waves, un- less it is largely removed, either by falling into deep water or by cur- 316 Geological Agencies. rents, from those sections where erosion is in progress, it soon forms a protective covering and prevents further effective wave action. 152. Glacial Erosion. — In the high mountains and in the poleward regions beyond the snow line where the summer heat is insufficient to melt the winter snows, snow fields are formed which by the accumu- lated pressure due to their great depths convert their lower portions into ice and force streams of ice slowly down the valleys (see Fig. 175), until the end of the glaciers reaches a region where the summer temperatures are sufficient to limit the glacial movement. (See Fig. 176. — End of the Great Glacier, British Columbia. Fig. 176). The effect of these slowly moving masses of ice may easily be imagined. They grind down the valley bottoms and sides and often shove before them or carry within their structure or on their surface the materials which they have eroded or which through other causes have become disintegrated or broken from the valley structures and become imbedded in or deposited on the glaciers. This material is slowly moved forward and is finally deposited at the end or side of the glacier where the ice within or upon which it is trans- ported is melted by the temperatures of the valleys which limit its ad- vance. When the end of the glacier remains in one position for a long period and its movement is continually depositing material at its terminus as the ice melts, it builds up deposits which vary from low ridges to con- siderable hills and are called terminal moraines. Such deposits fre- Glacial Erosion. 317 quently dam the waters of a valley from which the glacier has with- drawn and create lakes as in the case of the moraine below Moraine Lake in the valley of the Ten Peaks in British Columbia. (Fig. 177). When the glacier is retiring, due to increased temperature or decreased precipitation, no moraine marks its terminus unless it becomes stationary at certain points for considerable periods, but the material carried is distributed over the bed which it formerly occupied. Fig. 177. — Terminal Moraine at the Outlet of Moraine Lake British Columbia. (Fig. 176.) Often much of the finer material is carried away by the glacial waters which result from melting. In other cases the glacier reaches the ocean before melting and breaks off in icebergs which float away, carrying with them the materials contained in their mass. (See Fig. 178, page 318). While glacial action is of comparatively little importance at the present time in the United States, such work is still in progress in the mountains of. the northwest, and most of Greenland and much of the polar regions are covered with perpetual ice. Much of the United States and of the northern portion of Europe and Asia have been greatly modified by such action during periods when glacial conditions were much more extended than at present. 153. Movements of the Earth's Crust. — There are in general four ways by which the surface materials of the earth change their positions : First — By displacement or diastrophism when the crust of the earth is upheaved or depressed. 318 Geological Agencies. Second — By avalanches or landslides where unstable masses of rock slide into adjacent depressions. Third — By volcanic action or vulcanism when the earth's crust is rent and molten material is ejected. Fourth — By transportation when the material of the crust is broken, crushed, disintegrated and moved by the winds and waters from one region to another. Fig. 178. — Formation of Icebergs (see page 317). Diastrophism — The crust of the earth in many places rises and sink? but this action takes place so slowly that in few cases can the changes, he perceived except by comparison during long intervals of time. If the crust of the earth were uniform in elevation, the entire sur- face would be covered by water to an approximate depth of two miles. It is this diastrophic movement of the crust which has produced an un- equal surface and has given rise to the continents and islands. These land masses have changed and still are slowly changing their forms and extent as the surfaces rise, sink or perhaps remain stationary for a period of time. The main continent forming movements appear to have occurred prior to the formation of the earliest known sedimentary rocks. 1 There have been times in past geological ages when great lateral thrust has occurred, perhaps through the cooling and shrinking of the 1 See Chamberlain and Salisbury Geology, Vol. 1, p. 519. Movements of the Earth's Crust. 319 ■earth's interior, and the surface strata have been warped and folded into mountain chains. This has usually occurred near the continental borders. The resulting folds are sometimes upright and symmetrical but more often inclined and unsymmetrical, and the strata are so warped, twisted and faulted as to make the age of the strata in a given vertical section not always in accord with their positions. In ■other cases, great plateaus have been raised high above the oceans and more or less flexed, tilted and faulted but forming together vast high .and more or less level plains in which erosion lias had comparatively little effect in altering the main surface contours. These movements while still taking place are so slow that they have little effect in en- gineering works except that a knowledge of the conditions which have obtained in the past frequently furnishes a basis for understanding the •conditions which may be expected in carrying out such works. Fig. 179. — Dead Forest in Reelfoot Lake, Tennessee.3 There have been times, as in the case of earthquakes, when crust movements have been immediately apparent and when fissures were formed in the crust, and one side has dropped and the other has been uplifted, either or both of which has occurred at the same period. In an earthquake that occurred in Japan in October, 1871, there was a vertical displacement of from two to twenty feet that could be traced for forty-six miles, and a horizontal displacement at one point of as much as thirteen feet. 2 Sometimes such movements interfere with the movements of ground water, new springs are formed and old ones cease to flow, and occasionally ponds and lakes are formed. - Chamberlain and Salisbury Geology, Vol. 1, p. 510. 320 Geological Agencies In the earthquakes of 1811 and 1812 great depressions occurred near the Mississippi River in Kentucky, Tennessee, Missouri and Ar- kansas, and those areas became marshes and permanent lakes, in some of which standing trees are still visible. (See Fig. 179.) 3 One of the most disastrous earthquakes of modern times occurred near San Francisco in 1906. This was caused by a new slipping on the old fault plane which has been traced for a distance of about 180 miles. (See Fig. 180.) The horizontal displacement shown by the existing. \j5ar? Juan Wonfereu Fig. 180. — Fault Line of the San Francisco Earthquake of 1906. roads, fences, etc. (see Fig. 181), was considerable. Many buildings and engineering works, pavements, pipe lines, etc., were destroyed by the shock, but the principal losses were caused by the resulting serious conflagration which destroyed most of the City of San Francisco. 4 These disturbances are of great importance to the engineer who may have hydraulic works to construct in countries where earthquakes are liable to occur. Such structures must be carefully designed with such occurrences in view both for the safety of the structures and of the lives of the people which may depend upon such safety. Landslides — Masses of earth and rock on unstable slopes sometimes break away and slide into adjacent depressions. Conditions favorable to such occurrences exist where the masses overlie or consist largely of beds of soft incoherent material and especially where the bed joints are inclined toward the surface and the mass above has vertical jointing.. 3 The New Madrid Earthquake, hy M. L. Fuller. 4 The San Francisco Earthquake, by G. K. Gilbert, et al. Movements of the Earth's Crust. 32 The undercutting of streams and the saturation of the strata are factors which commonly make gravity effective in natural slides. In engineering works similar slides are caused by the weakening of strata by excavation for canals and railroad cuts or in mining and other works where masses of materials are removed from their natural beds. Such slides also occur in earth dams, reservoir embankments and levees where poor materials, improper construction or too great surface slopes are employed. Fig. 181. — horizontal Displacement During the San Francisco Earthquake shown by Road and Fence Line (see page 320 )A Vulcanism — Occasionally the crust has been rent by shocks, and molten matter is then sometimes ejected, pouring out in great streams of lava which spread over the surface and form extensive deposits. Such action at the present time has been extremely local in extent and outside of limited localities is of little importance to the engineer. Transportation — The runoff of the rainfall washes the sands and finer material from the mountains, hills and plains into the streams by which it is carried away and deposited on the lowlands, in the river channels or in the lakes and oceans where it is distributed by the cur- rents and waves and builds bars or forms new lands adjacent to the shores. Hydrology — 2 1 322 Geological Agencies. Transportation of material may occur in several ways. The fine fragmentary particles of the rock may be carried in suspension in the waters of the stream and the coarser portions may be rolled and pushed along the bed of the stream by the action of the current. Frequently the amount of the coarser materials that are moved along the bottom of the channel is very great. The amount of material so transported is dependent upon the velocity of the stream and its depth, together with the accessibility of material that can be carried. Fig. 182. — Deposits of Sand and Gravel behind the Danville Dam. Figure 182, shows the amount of material which had accum- ulated behind the dam at Danville, Illinois, in about a year after its construction. The dam built across the north fork of the Ver- million River was about thirteen feet in height and the stream which was of a somewhat flashy nature, during its rapid rises, not only car- ried a large amount of silt in suspension but also rolled along its bed large quantities of gravel and coarse sand which was stopped by the dam and accumulated until its top approached so near to the top of the dam that the velocity of the stream was sufficient to raise it over the crest. Hundreds of yards were deposited in this way, reducing the value of the storage pond which was formed by the dam. In this case the storage basin above the dam was not sufficient to prevent consid- erable current in time of flood and little or no silt was deposited except during very low floods. Movements of the Earth's Crust. 323 Large boulders and other debris from the disintegration of the rock masses may fall or slide from the valley sides and find lodgment upon the river ice, or the ice may freeze to boulders along the bottom and shores of a stream, and upon breaking up in the spring, may trans- port them considerable distances. In the same way material is re- TABLE 36. Matter Carried in Solution and Suspension oy Various River Waters of the United States. Parts per million Stream Location In solution In suspension Arkansas Kittanning, Pa 82 100 Allegheny Little Rock, Ark Big Vermillion Danville, 111 Brazos Waco, Texas 1,136 Cedar Cedar Rapids, Iowa Chippewa Eau Claire, Wis Colorado Austin, Texas Cumberland Nashville, Tenn Fox Ottawa, 111 Hudson Hudson, New York Illinois LaSalle, 111 Kentucky Frankfort, Ky Mississippi Dayton, Ohio Mississippi Minneapolis, Minn Mississippi Quincy, 111 Missouri Memphis, Tenn North Platte Florence, Nebr Ocmulgee No. Platte, Nebr Potomac Macon, Ga Red Cumberland, Md iSt. Lawrence Shreveport, La Savannah Ogdensburg, N. Y Susquehanna Augusta, Ga Tennessee Danville, Pa Wabash Knoxville, Tenn Tennessee Logansport, Ind ceived and transported by glaciers. The great glaciers of past ages had an exceedingly great influence upon the topography of the regions which they covered, by their transportation of vast amounts of ma- terial. The wind in certain regions of the globe is an important agent in the transportation of sand and dust. Examples of the action of wind in its effect upon the topography may be seen in the great shifting sand dunes of the Carolinas and Michigan, and in a number of places in the arid portions of the United States and other countries. The transportation as effected by stream flow may cause either deg- radation or aggradation, depending upon whether the stream is pick- ing up and carrying its load of detritus or because of reducing velocity or 630 748 281 82 ,136 488 228 61 90 4 321 351 119 94 335 87 108 16 278 136 104 142 289 94 200 8 203 119 202 519 454 2,059 295 311 69 174 130 29 561 870 134 T. 60 142 112 21 112 156 807 117 324 Geological Agencies. volume is unable to carry the load farther, and deposits it, thus building up its bed. The average amounts of matter in solution and in suspension in parts per million carried by various rivers of the United States as deter- mined during the years 1906-07 were as shown in Table 36. 5 154. Results of Erosion. — Table 37 shows the estimate of C. C. Babb 6 of the average amount of sediment carried in suspension by large rivers of the world to which has been added in the last column the number of years required to reduce the drainage area one foot at the rate given. In the process of erosion lakes are but temporary features ; in the lapse of time, their outlets become so lowered that they are drained, TABLE 37. Discharge and Sediment of Large Rivers. Mean an- Sediment Years re- Drainage nual dis- Depth over quired to River area charge Total an- Ratio by drainage reduce sq. miles sec. ft. nual tons weight area in. area 1 ft. Potomac 11,043 20,160 5,557,250 1:3575 .00433 2,774 Mississippi .. 1,214,000 610,000 406,250,000 1:1500 .00288 4,170 Rio Grande. .. 30,000 1,700 3,380,000 1:291 .00110 10,900 Uruguay 150,000 150,000 14,782,500 1:10,000 .00085 14,100 Rhone 34,800 65,850 36,000,000 1:1775 .01071 1,120 Po 27,100 62,500 67,000,000 1:900 .01139 1,052 Danube 320,300 315,200 108,000,000 1:2880 .00354 3,390 Nile 1,100,000 113,000 54,000,000 1:2050 .00042 28,600 irrawaddy .. 125,000 475,000 291,430,000 1:1610 .02005 600 and the material carried by the waters of the rivers eventually reaches the sea. The waves of the lakes and the oceans as they beat against the shores erode the cliffs and spread the coarser material along their margins (see Fig. 174, p. 315) which in turn is worn by wave action and trans- ported by the waves, currents and tides and formed into new deposits. The ultimate results of unchecked erosion would be to reduce the land surface nearly to sea level. Gradually and more and more slowly as the gradient is decreased by erosion, the topographical features of the land are reduced and the process would result in a featureless pene- plain or base level with just sufficient gradient to discharge the rain waters into the sea. These ultimate results from erosion on the land areas during the past geological ages have never been more than ap- 5 Water Supply and Irrigation Paper No. 236. The Quality of Surface Water in the United States, R. B. Dole. s Science, 1893; Vol. XXI, p. 343; also Eng. News, 1S93, p. 109. Results of Erosion. 325 proximatecl as the conditions of erosion have ever been modified, ac- centuated or destroyed by diastrophic movements, upheavals or de- pressions of the earth's crust which have either raised the land areas more or less and given greater opportunities for further erosion or have sunk them nearer or below the sea level where new deposits were per- haps laid down over them, obliterating such previous erosive effects as may have remained. 155. Origin and Development of Drainage Valleys. — Wherever land surfaces have appeared above the sea, drainage systems have soon been established. The original drainage lines have either followed natural depressions in the crust or depressions that have resulted from lines of structural weakness where normal erosion has been compara- tively rapid. Extensions of the systems of drainage have resulted from further erosion which must normally proceed most rapidly along lines of weak- ness caused by weak strata or by other causes which have reduced re- sistance and increased erosion, and which proceed slowly when the strata are resistant and when other causes of erosion are retarded. In this way the original drainage development of a country may, with the passage of time, be radically changed and areas drained by one stream in which erosion has been held in check, may be seized by the tribu- taries of a different stream where erosion is more rapid. In the same manner the tributaries of a main stream are pushed far- ther and farther toward the divide and frequently even into lands be- yond, until a complete system of drainage may effectively be provided for thousands of square miles of territory. Such systems have been frequently altered and changed by diastrophism, vulcanism and glacia- ion. At any one time the larger streams are the result of ages of ero- sion and geological change and represent within their length, all stages in river growth. Where the strata in which a stream develops have approximately uni- form resistance, a normal stream bed having a concave profile is de- veloped. (Fig. 183). The gradient of the lower portion on account of its age and larger flow, has reached a less inclination at or approximating its base level. The middle course being younger has a higher gradient and a considerable flow, and here maximum corrasion usually occurs. The upper portion being of more recent origin and with a small amount of flow except at times of flood, has a high gradient. Streams with high gradients and consequent high velocities are able to transport considerable amounts of sand and heavier rock material 326 Geological Agencies. ! * J 1 & / M w M i rai°y It 3/ h U t-ll? £< jtOjjy^ uO* oi > €^ $ \ W? ^"' vV» ^J 7^ \ J * y ^r j Fig. 183.— Stream Profiles. Fig. 184. — Vertical Erosion of the Colorado River. which corrade their beds and result in comparatively rapid vertical and small horizontal erosion. (See Fig. 184.) The work of streams with low gradients is largely confined to working over the material in their Drainage Valleys 327 beds and banks. During periods of floods the excess energy in their waters excavate their channels (see Fig. 185) and destroy or rearrange their banks (see Fig. 186), and frequently rearrange their local channels. (See Figs. 202 and 203, page 340.) With the subsidence of the flood stage large amounts of sediment are deposited, old channels are filled and excavations in their beds are restored. The study of the work of streams is highly important in connection with the design of river con- servancy and flood protection work. 1020- \ \ /ooo- $ 990 S ■8 980 I 970 l •8} Uj 960 Aug 18 July 21 April 16 Spring < Culmination q[ Rise June 23 June, Rise July 12 Sand Mixe>d u/ith C/au Sandy Clay 2 Gumbo \ ^-'Carboniferous - ^Coar se Sand- Limesto ne : ■- ^^As^iASXi ^V? Fig, O / 2 3 4 5 6 7 185. — Variations in Cross Section of the Missouri River at Omaha.* 156. Origin of Falls and Rapids. — When, in the development of a river, strata are encountered that have comparatively higher resistance, corrasion at such points becomes slow and falls or rapids result. A pool is soon formed below the resistant strata as the water with its sediment and the matter pushed along the bottom plunges over the resisting de- posit onto the yielding strata below ; and where the conditions are favor- able, a permanent fall results. In such cases the normal concave profile will be modified locally to a greater or less extent. (See profile of the Little Colorado River.) In most cases, the ordinary inequalities in the strata of the stream bed create a condition of alternate pools and rapids which, however, often become comparatively insignificant and are more or less obscured when the flow is considerable. The resisting strata which produce a falls or rapids may be a local inequality of limited extent, such as concretions or boulders, or it may be interbeded strata of high resistance. (Fig. 187, A and B, page 1329. ) Falls and rapids may result from an intrusive strata such as a dike of *J. E. Todd, Bulletin 158, U. S. Geol. Survey. 328 Geol eologica 1 A gencies resistant material which crosses the stream bed (Fig. 187 D) or where more Or less horizontal strata of high resistant quality are inclined in the direction of or opposed to the flow of the stream. (Fig. 187 C). Fig. 186. — Shifting Channel of the Missouri River near Florence, Nebraska (see page 187). Fig. 188, page 329, shows an intrusive dike across the Kicking Horse River near Field, British Columbia, which formerly created a fall at that point. The water has at the present time worn a way through the dike (see Fig. 189) and the fall is just behind it. The dike is now known as a natural bridge. Yielding strata below the resistant rock are more rapidly eroded Drainage Valleys. 329 while strata above the obstruction are in some degree protected by the lesser gradient that obtains above the fall. In any event, gradual degradation will occur at the crest of the fall which will slowly retire Fig. 187. — Falls and Rapids Fig. 188. — Intrusive Dike across Kicking Horse River, British Columbia ( see page 328). upstream as the resistant rock yields to corrasion. Sometimes the re- sistant rock is a comparatively thin deposit underlaid by yielding strata, as in the case of the Falls of Niagara. 7 (Fig. 190 A and B. ) In such cases the underlying yielding rock may be eroded by the corra- sion of the waters or disintegrated by weathering, leaving the superim- posed resistant strata overhanging and supported only by its transverse Rate of Recession of Niagara Falls, G. K. Gilbert. Bui. 306, U. S. G. S- 330 Geological Agencies. Fig. 189. — Natural Bridge on Kicking Horse River, British Columbia. strength. When the unsupported weight is sufficient, the stratum is fractured and falls, and the crest of the fall recedes upstream. (See Fig. 191, p. 332.) Should the resistant strata run out and be worn through, the falls rapidly disappear. A rapids first results which is quickly degraded as the yielding rock erodes. This nearly occurred at St. Anthony's Falls Drainage Valleys. 331 on the Mississippi River at Minneapolis where the limestone cap was almost totally eroded, in which case the underlying sandstone would have been exposed and the fall would have disappeared. It was only by considerable labor and expense that the remaining rock was pro- tected and the fall thus artificially saved for water power purposes. In glaciated areas the whole drainage topography has been modified and largely or entirely destroyed, a new topography has resulted, and numerous falls and rapids have been developed. In Wisconsin the preglacial valleys have been filled with clays, sands, gravels and boul- ders for 200 feet or more. On the recession of the glaciers a new drainage system began to develop and the country still presents the ap- Fig. 190. — Falls of Niagara (see page 329). pearance of topographical youth. Even when the new streams partially occupy old valleys and flow over materials which are easily eroded, erosion is frequently held back by obstructions at the outlets. The lower Wisconsin River, for example, flows over a yielding deposit 200 feet or more in thickness, but the river at its lower end has reached its base level on account of the obstruction by the gradient of the Missis- sipi River. In many places, these new streams in rapidly eroding their chan- nels through the yielding drift material, have encountered rock. At such points erosion is delayed, while it rapidly proceeds in the stretch below the ledge. The result is the development of falls like those on the Peshtigo River at High Falls (see frontispiece, upper figure), where a drop of over forty feet has been formed. This drop with the smaller falls and rapids above, permitted a hydraulic development of over eighty feet at this point. (See frontispiece, lower figure.) The development of a fall or rock rapids in glaciated country indi- cates that the stream bed is not over the thalwag of the preglacial stream and is an indication that the lowest outlet past the ledge has not been 332 Geol eolosica 1 A gencies. uncovered by the modern stream. Sometimes the rock outcrop oc- curs where the stream has turned through a gap in preglacial hills and the channel is then safely protected from radical changes as in the case of the Rock River at Rockford, Illinois, where the original channel ex- tends to the southward while the modern stream turns through a sad- dle in the hills to the southwest. The Mississippi River at Rock Island Fig. 191. — Recession of Horseshoe Fall (see page 330). Average annual recession from parallel ordinates from areas 4.0 4.4 6.6 5.6 5.3 5.3 Period Limiting dates years 1842-1875 33 1875-1905 30 1842-1905 63 Rapids above Moline, Illinois, is also an example of such a change in course. Sometimes the rock outcrop which produces the falls is on an ancient hillside and in such cases a dangerous condition may result under which, with unusual floods the stream may radically change its course. Such a change took place in the flood of October, 191 1, at Black River Falls, Wisconsin. (See Fig. 192.) A view of these falls before and after the flood is shown in Fig. 193, page 334. The Black River at this point flows over a rock out-crop on a pregla- cial hillside. A dam had been built at this falls, the north end of which abutted against glacial drift which was not properly protected. The flood waters rising over the abutment readily cut away the drift material and the river turned around the end of the dam into the Drainage Valleys. 333 lower portion of the city, destroying many buildings and much prop- erty. (See Fig. 194, page 335). When the river was turned back into its course by the construction of a diverting and retaining wall across its new channel, the surface of the rock under this wall was found to be fifty feet below the rock of the dam site. Even in a glacial drift, the boulder clay is so resistant that the smaller streams erode it with difficulty and occasionally excavate the clay around boulders so large that they cannot be transported by the stream. This may finally result in such a resistant mass of boulders that a considerable rapids may be developed. (See Fig. 195, page 335). Fig. 192. — Rock Conditions at Black River Falls. The water pouring over the brink of a fall develops considerable en- ergy which is expended in impact and eddying in the waters below. Erosion is here materially augmented by the rocks, sand and gravel carried over the falls by the stream. The bed below a fall is therefore frequently excavated to a considerable depth below the stream surface. At the Horseshoe Falls of Niagara, the drop of the lower stream sur- face is about 170 feet, but the water below the fall is approximately 200 feet in depth, the bed being eroded in the softer material to this depth bv the tremendous energy of the falling waters. (See Fig. 190A, page 331). The quantity of water which passes over the American side is not however sufficient to remove the fallen material from below. (See Fig. 190B.) In the construction of dams the energy of the stream is frequently artificially concentrated in the same manner, and in such cases it is important to protect any yielding strata below the dam by a properly constructed apron or other protective work. 334 Geological Agencies. I o '•a o o pq Drainage Channels. 335 Fig. 194. — New Course of River at Black River Falls (see page 333). Fig. 195. — Boulder Bed of Wolf River (see page 333). 157. The Origin of Lakes. — Lakes are of various origins and may in general be classified in accordance with their origin as follows : A. Diastrophic Lakes. — Caused by accumulations of surface water in the depressions which are due to displacement of the crust of the earth. B. Crater Lakes. — Formed by accumulations of surface water in the craters of jextinct volcanoes. 336 Geological Agencies. C. Glacial Lakes. — Formed in the topographical depressions carved by gla- cial action; caused by the obstruction of a valley by a terminal mo- raine or by tbe depression left by the melting of the glacier itself. D. Bayou Lakes. — Occasioned by the cutting off and subsequent silting up of the extremities of a bend in a stream. E. The damming of a water course by landslide or similar earth movement. F. Obstructions formed across a river by deposition of material as a delta at the mouth of a tributary. G. Basins due to chemical action such as solution of material to form a de- pression in limestone. H. Basins excavated by the wind. Inland lakes are subject to a further classification, depending in- large measure upon the climate in which they occur. Observations show that with the proper topographic conditions a low rate of rain- fall together with a relatively high rate of evaporation frequently re- sults in lakes which can not rise sufficiently to overflow their basins, and the continued concentration of the mineral content of the water pro- duces a salt lake. Ordinarily lakes that are provided with an overflow or outlet are composed of fresh water. The largest inland body of water on the globe, the Caspian Sea, is salt, while the second largest, Lake Superior, is fresh water. The Great Lakes of North America are diastrophic in origin, al- though glacial action had much to do with their present form. It is probable that the valleys of these lakes were formerly drained by riv- ers forming a part of the preglacial St. Lawrence River system (Fig. 196, page 337). Later, during glacial times, a single lake probably oc- cupied the valleys of Lakes Michigan, Huron, and Superior, and Lake Ontario was considerably extended. (Fig. 197, page 338). The lake system changed its form and outlet at various times during the glacial age. On the recession of the glaciers, this system was gradually drained, resulting in the system as it now exists. A section along the Great Lakes is shown in Fig. 198, from which it will be seen that if the lake section was the result of the de- nudating effects of river drainage that disastrophism has since pro- duced a reverse gradient in the valleys of the three upper lakes. Crater lakes are comparatively few and only of local importance. The best example of these lakes in America is Crater Lake in Oregon which is over six miles in its greatest diameter and has a maximum depth of almost 2,000 feet. (See Fig. 199.) Glacial lakes are very numerous within the glaciated boundaries of the United States. Thousands of these lakes are found within the terminal moraine in Wisconsin, Minnesota and other states. These- Origin of Lakes. 337 Fig. 196. — Preglacial St. Lawrence River Drainage (see page 336). «fc?v. L ourentide Jce Jfieef Fig. 197. — Glacial Lake Algonquin (see page 336), Hydrology — 22 338 Geological Agencies. lakes are frequently of importance as sources of water supply, sites for storage reservoirs and pleasure resorts. Some idea of their great num- ber may be obtained from an examination of the map of the head- waters of the Wisconsin River. (See Fig. 200, page 339.) S/ofeSt I I ^ *> $ ^ t$ "S Hi -C; to/re J< ia&e M/cfr/gar? $>Lo/re //uron^ § ,J> Er/e s s § 5> Fig. 198. — Section through the Great Lakes. Fig. 199. — Crater Lake, Oregon (see page 336). Lakes are sometimes formed in a stream valley by the building of obstructions to flow from the deposition of material brought to the stream by a tributary. Lape Pepin (see Fig. 201, page 339) on the Mississippi, formed by the deposits from the Chippewa River in Wis- consin, is an example of this action. The formation of this lake caused a retardation of the current of the Mississippi and a deposition of the materials conveyed by its waters when it entered the northern end of Lake Pepin, and resulted in a local delta formation and the form- ation of several minor lakes therein. This delta deposit has filled Lake Origin of Lakes. 339 Lakes +f Marshes i Fig. 200. — Intermoraine Lakes of Upper Wisconsin River Valley (see page 338). Fig. 201. — Lake Pepin (see page 338). Pepin from a point near the mouth of the St. Croix River to which it probably extended at one time, to its present northern extremity near Bay City. The Mississippi by the deposits has dammed the outlet of the St. Croix to a depth of fifty feet or more, causing the formation of Lake St. Croix which is twenty-three miles in length and fifty feet or more in maximum depth. 340 Geological Agencies. Fig. 202. — Lake at Eau Claire, Wisconsin (see page 341), Fig. 203. — Bayou Lakes on the Pecatonica River, Illinois (see page 341). Origin of Lakes. 34 Bayou lakes (see Figs. 202, page 340 and 203, page 340) and bayous still connected at their lower ends with the river are often found when both or only one of the extremities of a meander which has been cut off are filled by deposits. These are of common occurrence in regions of /7f wafer u Wot/pun Chester Jf JL t A Le f?ou Burnett Junction \ toV . Farmersw'f/e > * D * , * 1 nehoskee Mayvi/te I 2 3 5ca/e in Mi/es Beai/er Dam -SL^£±_^jM/nn\sofa Ro///nq Prairie — ■ ffl June fy on fior/con Pig. 204. — Example of a Silting Lake, Horicon Marsh, Wisconsin. flat gradients and extensive flood plains. Lakes due to landslides and to chemical and wind action are of more limited occurrence and only of local importance. 158. Permanency of Lakes. — Ordinarily the lakes of a humid re- gion are relatively short lived. The tributary streams bring in large amounts of sediment which are practically all deposited during the slow passage of the water through the lake, and the deposits of the re- 342 Geological A gencies. mains of plant and animal life all tend toward rilling the lake bed. (Fig. 204). 8 The outlet stream has a continual cutting tendency to lower the elevation of the outlet, and thus drain the lake. This factor is usually of less importance than the sedimentation be- cause of the fact that the outflowing stream usually contains little detritus and its eroding ability is correspondingly less. The result of these actions is to form an alluvial plain in the lake bed through which the stream pursues a sinuous course. When this condition is reached, the outgoing stream carries a considerable load of sediment and the Cross 5ecl/on -13.70 Miles aooie Oom Fig. 205. — Silting of Lake McDonald, Austin Dam, Texas. rate of corrasion is accordingly increased so that eventually all traces of the lake are removed by the lowering of the stream bed. Sedimentation is continually going on in artificial lakes or reservoirs,, constructed for the storage of water for irrigation, water power and other purposes; and where the material carried by the stream is con- siderable the reservoir may soon become silted up and useless. 9 By the construction of a dam across the Colorado River at Austin, Texas, a reservoir about nineteen miles in length was created. When the dam was completed in 1893, this reservoir had a capacity of 83.5 million cubic yards of water. In I897 this capacity had been reduced 38 per cent by silting, and in 1900 the reduction was equal to 48 per cent of the original capacity (see Fig. 205). Salt lakes of the arid regions commonly have longer existence than those of the humid regions, since sedimentation does not decrease the s Physical Geography of Wisconsin, by Lawrence Martin. 9 See Denudation and Erosion in the Southern Appalachian Region, by L. C. Glenn, Professional Paper No. 72, U. S. Geo. Survey. Permanency of Lakes. 343 volume of water except as the rise it causes exposes a greater area to the effects of evaporation. Traces of extinct lakes in the arid regions are more enduring than those situated in the humid regions, since the erosion and other weathering effected by the rainfall is not so rapid. That fresh water lakes existed upon the face of the earth in remote geological ages is known by the deposits that were laid down and the fossil remains found in these deposits. Lakes more extensive than any Fig. 206. — Glacial Lake Agassiz. Fig. 207. — Lakes Bonneville and La- hontan. now known probably existed in the Cordilleran regions. Sediments to the depth of several thousand feet were laid in some of them. Their bottoms have since been upheaved to form mountain ranges, and all traces of their shore lines have been obliterated. Remains of fairly recent lakes in the United States are still quite discernible. Three of the largest and best known of these are Lake Agassiz, Lake Bonneville, and Lake Lahontan. Figures 206 and 207, are maps showing the outlines of these lakes so far as has been determined. Lake Agassiz is believed to have been formed by the great ice sheet which dammed the drainage of the Winnipeg basin and caused the waters to rise, until a southward drainage was opened through glacial River Warren, about where the Minnesota River is lo- cated at present. 344 Geological Agencies. Lake Bonneville was situated on the east side of the Great Basin in the region where Great Salt Lake now lies. The waters from this basin overflowed northward through the Snake River into the Colum- bia. Its fluctuations are plainly marked by beaches upon the hills. (Fig. 208.) Lake Lahontan occupied the western side of the Great Basin, and is at present represented by Pyramid, Winnemucca, Walker, Carson and Humboldt lakes in Nevada, and Honey Lake in California. This lake probably had no outlet. Its fluctuations are marked by great de- posits of tufa composed principally of calcium carbonate. On favor- Fig. 208.— Terraces. Great Salt Lake. able localities this deposit may be seen to be over eighty feet in thick- ness. 159. Changes in the Extent of Lands.— The changes that have oc- curred and are now occurring in the limits of continental boundaries and the extent of the land surface are due to the factors already con- sidered. Of these diastrophism, or the rising and sinking of the crust, is perhaps the most important. The change in the relative elevation of the sea level has also been an important factor. These changes have been caused not only by diastrophism but by the extension of the shores and the filling up of the lakes and seas by the materials resulting from the denudation of the land, and also perhaps during the glacial epoch by the extraction of large quantities of water from the ocean by evapo- ration and its storage as snow and ice in the great glaciers that have from time to time accumulated in polar regions and overrun consider- able portions of the Northern and perhaps the Southern Hemisphere. A former extension of the eastern coast at some time in the past is illustrated by Fig. 209, page 345. which shows the continental shelf Changes in Extent of Lands. 345 346 Geological Agencies. 1 zoo \B T ~"—- I 1 k ^^ too i \o 1 \-x 600 1 1 000 £ ^-^r*v c^ 1000 1? ^ laoo 1100 Ati/as .«„_ i t 1 ■3 2 3 * a i s 6 7a/ Secf/os? =s \ f -— ~ \ - 1 s ■ — N »l > s I f 1 ' \ ^ IS \ J f \ / J / , J / Miles Mi ts Mi E-S f/lc s L ; C/2 3*Jfc7SO/£3V5'«780/ 23*5^6 730/2 J* 56 7 8 A 3 a £> Cross £iec//o/7s Fig. 210. — The Submerged Valley of the Hudson River (see page 347). Changes in Extent of Lands. 347 along the eastern United States, the limits of which mark the former boundary of the continent. Proof of this is furnished by the fact that many of the valleys of the eastern river systems can be traced to the edge of this shelf, and it is clear that these valleys could have been formed only by atmospheric and eroding agencies during the time that Ancient V/l/ioqes /ost bu Sea 1 o Auburn 2 o tiarfburn 3 o fiude or Hyfb 4 o C/e/on or C/outon 5 o Wifhow Hornsea Becft Fig. 211. — Changes in the Yorkshire Coast, England. this portion of the continent was above sea level. The valleys of the St. Lawrence, the Hudson, the Delaware, and the former Chesapeake River have been traced far out to sea. The condition of the ancient valley of the Hudson, as shown in Fig. 210, page 346, illustrates sim- ilar conditions that prevail in many places. The changes in the land surface by erosion of the waves and by the deposition of material eroded from the exposed surfaces is and always has been of great importance. Mr. E. R. Matthews states 10 that there is hardly a county of the east coast of England that has not had numerous towns and villages de- 10 Proc. Inst, of Civil Eng., Vol. 159, p. 77. 348 Geological Agencies. stroyed by the waves during the last few centuries, and he estimates this loss at approximately 1,800 acres per annum. Mr. Matthews es- timates that the loss along the Yorkshire Coast has been at least nine feet per annum, and that the loss since the Roman invasion has been approximately as shown in Fig. 211. In many cases material accretions are added to the lands by wave and current action, for example Dungeness Point on the south shore of England is said to have extended seaward over nine feet per annum between 1795 and 1850, thirteen feet per annum between 1850 and * lamp J New land areas Mew water areas O I Z 3 4 S Mi'/es. Fig. 212. — Lower End of the Delta of the" Mississippi River. 1 87 1, and eight feet per annum between 1871 and 1897, and that in consequence the light house had to be shifted three times during the past century. The extended growth of deltas at the mouths of large rivers is illus- trated by Fig. 212, n page which shows the lower end of the Delta of the Mississippi River. The Delta receives about 400,000,000 tons of sedi- ment every year and is being built out into the sea at an estimated average rate of about 300 feet a year. 11 Mud Lumps at the Mouths of the Mississippi, E. W. Shaw. Prof. Paper S5— B, U. S. Geological Survey. Literature. 349 LITERATURE GENERAL Physiography of the United States, J. W. Powell and others, 1896, American Book Company, New York. College Physiography, R. S. Tarr & L. Martin, 1917, MacMillan Co., New York. Physiography, R. D. Salisbury, 3d Ed., 1913, Henry Holt & Co., New York. The Physical Geography of New York, State, R. S. Tarr, 1902, The MacMillan Co., New York. Physical Geography of Wisconsin, Lawrence Martin, 1916, Bui. No. 36, Wis- consin Geological and Natural History Survey. Geology, T. C. Chamberlain & R. D. Salisbury, 3 vol., 1906, Henry Holt & Co., New York. Vol. 1, Processes and Their Results. Geology, Physical and Historical, H. F. Cleland, 1910, American Book Co. Text Book of Geology, Part I, Physical Geology, L. V. Pirsson, 1915, John Wiley & Sons, New York. North America, I. C. Russell, 1904, D. Appleton & Co., New York. Geology and Its Relation to Topogmphy, J. C. Branner, Trans. Am. Soc. C. E., 1898, Vol. 39, p. 53. Some Illustrations of the Influence of Geological Structure on Topography, R. S. Lyman, Jour. Franklin Institute, May, 1898, p. 355. The Interpretation of Topographical Maps, R. D. Salisbury & W. W. Atwood, Prof. Paper No. 60, U. S. Geol. Survey, 1908. GLACIERS Glaciers of North America, I. C. Russell, 1901, Ginn & Co., Boston. Existing Glaciers of the United Spates, 5th Annual Report, U. S. Geol. Survey, 1883-4, p. 309. The Rock Scorings of the Great Ice Invasions, T. C. Chamberlain, 7th Annual Report, U. S. Geol. Survey, 1885-6, p. 155. Glacier Bay and Its Glacier, H. F. Reid, 17th Annual Report, U. S. Geol. Sur- vey, 1895-6, p. 421. Glacial Sculpture of the Big Horn Mountains, Wyoming, F. E. Matthes, 21st Annual Report, U. S. Geol. Survey, 1899-1900, Part 2, p. 167. Preliminary Paper on the Driftless Area of the Upper Mississippi River Val- ley, T. C. Chamberlain & R. D. Salisbury, 6th Annual Report, U. S. Geol. Survey, 1884-5, p. 199. Glaciers of Mt. Ranier, G. O. Smith, 18th Annual Report, U. S. Geol. Survey, 1896-7, Part 2, p. 349. The Glacial Gravels of Maine and Their .Associated Deposits, C. H. Stone, Monograph 34, U. S. Geol. Survey, 1899. The Illinois Glacial Lode, Frank Leverett, Monograph 38, U. S. Geol. Survey, 1899. Drainage Modifications in S. E. Ohio and Adjacent Parts of West Virginia and Kentucky, W. G. Tight, Prof. Paper No. 13, U. S. Geol. Survey, 1903. Pre-Glacial Valleys of the Mississippi and Tributaries, Frank Leverett, Jour, of Geology, Vol. 3, p. 740, 1895. The Lower Rapids of the Mississippi River, Frank Leverett, Jour, of Geology, Vol. 7, p. 1, 1899. 350 Geological Agencies. EARTH MOVEMENTS Earthquakes Recent Earth Movements in the Great Lake Region, G. K. Gilbert, 18th Report U. S. Geol. Survey, 1896-7, Part 2, p. 595. Earthquakes, W. H. Hobbs, 1907, D. Appleton & Co., New York. New Madrid Earthquake, M. L. Fuller, Bui. 494, U. S. Geol. Survey, 1912. San Francisco Earthquake, G. K. Gilbert and Others, Bui. 324, U. S. Geol. Sur- vey, 1907. The Charleston Earthquake of August 31, 1886, C. E. Dutton, 9th Annual Re- port, U. S. Geol. Survey, 1887-8, p. 203. The Kingston Earthquake, C. F. Marvin, Monthly Weather Review, Jan, 1907, p. 5. The Water Supply of San Francisco, Before, During and After the Earthquake of April 18, 1906, Herman Schussler, 1906, Spring Valley Water Co. Landslides Engineering Geology, H. Rice and T. L. Waters, Chap. VII, Landslides (with references), John Wiley & Sons, 1914. Landslides and Rock Avalanches, G. E. Mitchell, National Geographic Maga- zine, 1910, Vol. 21, p. 277. A Suggested Method of Preventing Rock Slides, G. S. Rice, Jour. West. Soc. of Engineers, 1913, Vol. 18, p. 585 (with many references). The Rivers of North America, I. C. Russell, 1902, G. P. Putnam & Son, New York. Physics and Hydraulics of the Mississippi River, Humphrey and Abbot, Prof. Papers of Corps of Engineers, U. S. Army, No. 13, 1864. The Improvement of Rivers, Thomas and Watt, John Wiley & Sons, 1913. River Hydraulics, James A. Seddon, Trans. Am. Soc, C. E., Vol. 43, 1900, p. 179. The Hydrography of the Potomac River, Cyrus C. Babb, Trans. Am. Soc, C. E., Vol. 27, 1892, p. 21, see also Eng. News, Vol. 30, Aug. 10, 1893, p. 109. Erosion of the River Banks of the Mississippi and Missouri Rivers, J. A. Ocker- son, Trans. Am. Soc, C. E., Vol. 28, 1893, p. 396 and Vol. 31, 1894, p. 26. Limiting Waves on Meander Belts of Rivers, H. S. W. Jefferson, National Geographic Magazine, Oct., 1902. The Atchafalaya River, Some of Its Peculiar Physical Characteristics, J. A. Ockerson, Trans. Am. Soc, C. E., Vol. 58, 1906, p. 1. Transportation of Solid Matter by Rivers The Suspension of Solids in Floiving Water, E. H. Hooker, Trans. Am. Soc, C. E., Vol. 36, 1896, p. 239. Transportation of Solid Matter by Rivers, Wm. Starling, Trans. Assn., C. E. of Cornell Univ., June 18, 1896. Methods and Conditions of Transportation of Sediment, Wm. Starling, Eng. Mag., November, 1892. Silt Movement of the Mississippi, Its Volume, Cause and Condition, R. E. McMath, Van Nostrands Eng. Mag., Vol. 28, p. 32. Literature. 351 Erosion of River Beds and Transportation of Detritus, G. K. Gilbert, Eng. News, Aug. 19, 1876. Lakes, Harbors, Etc. Lake Bonneville, G. K. Gilbert, Monograph No. 1, U. S. Geol. Survey, 1890. Lake Lahontan, J. C. Russell, Monograph No. 11, U. S. Geol. Survey, 1885. The Glacial Lake Agassis, Warren Upham, Monograph No. 25, U. S. Geol. Sur- vey, 1896. Lakes of North America, I. C. Russell, 1904, Ginn & Co., Boston. Geological History of Harbors, N. S. Schaler, 13th Annual Report, U. S. Geol. Survey, 1891-2, Part 2, p. 93. CHAPTER XIV GEOLOGY 160. Object of the Study of Geology. — The primary object of the hydraulic engineer in the study of geology is to determine the structure of the earth insofar as such structures will influence his work in rela- tion to : i. The conditions favorable or adverse to the presence and perman- ency of surface or ground waters and their control or disposal. 2. The discovery, selection and utilization of adequate water sup- plies. 3. The storage and distribution of waters. 4. Securing and maintaining the qualities of water necessary for sanitary and economic purposes. 5. The reclamation and protection of communities, lands, structures and channels from the presence or encroachment of normal and abnor- mal waters. 6. The selection of sites desirable for safe and economical construc- tion of dams, reservoirs and protection work. The presence of surface waters and the flow of streams depend not only on the quantity and distribution of the rainfall but on the geologi- cal structure of the drainage area and the amount of water which on ac- count of such structure will flow from the area without entering the ground, or which will be delivered to streams or lakes from the pervious deposits without sinking into the deep underlying strata entirely below the bed of the drainage system. Navigation, water power, irrigation and water supply engineering depend primarily upon the availability of sufficient water either from surface streams or underground sources, both of which are largely de- pendent upon geological structure. The occurrence of surface waters is obvious, but the possibilities of the presence of underground waters can be determined only by a knowl- edge of the local geological conditions. The presence of such waters and their character can often be inferred and often definitely deter- mined, without expensive pioneer exploration by a knowledge of the geological conditions of the country. The practicability of successful storage of waters depends upon the Object of Study. 353 nature of the foundation of the dam or embankments built to retain them and the character of the bed and banks of the ponds or reservoirs so created. The presence of cracked, fissured, faulted or cavernous rocks or of pervious deposits may make such structures impracticable either from the expense involved in the construction and maintenance of the work necessary to correct the unsatisfactory condition or on ac- count of the excessive losses of water due to percolation. The feasibil- ity of the distribution of waters through open channels for water sup- plies and navigation depends also upon the presence of favorable or un- favorable deposits and the condition of the materials through which such channels are to be constructed. The mineral content of water depends on the mineral character and solubility of the geological deposits through which water flows from the catchment area to the point of utilization. Its sanitary character de- pends upon the conditions encountered in its flow which may be favor- able either to the maintenance of organic purity or % to its contamination by the wastes of civilization and manufacturing. The protection or reclamation of lands from normal and occasionally abnormal conditions of flood and drought to which they may be subject is largely determined by the topography and structure of such land. The foundations of structures and the suitability of sites for safe and economical construction and maintenance of dams, reservoirs, canals and their appurtenances are largely questions of topographical and geological conditions. In all cases topographical conditions are more or less evident and can be determined in detail by surveys. Geological conditions can be de- termined only by expensive exploration and borings, which expense, however, can often be largely curtailed by a knowledge of local geology and of geological principles. Frequently even extensive exploration will not give the information needed without the interpretation which can be furnished only by geological knowledge. 161. Rock Masses and their General Classification. 1 — In general all materials forming part of the earth's crust, whether consolidated or unconsolidated, are termed rocks. These rock masses may be classified into four principal groups : i. Archean Rocks, which while probably not parts of the original crust of the earth, constitute the earliest known rocks. The Archean rocks are believed to be the foundation over which later rocks were de- Physiographic Processes, J. W. Powell, p. 11. Hydrology — 23 354 Geology. posited and the source from which the sedimentary rocks have been most largely derived. 2. Volcanic Rocks, which result from flows of melted lava that have issued from the interior of the earth through volcanoes and volcanic fissures. 3. Sedimentary Rocks, which have been formed in the sea by the dep- osition of materials due to the denudating influence of atmospheric and hydrological agencies which continually act with destructive effect on preexisting rock beds and on the resulting decomposed material dur- ing its transportation. These materials have been deposited in more or less changed forms and have served to build up new strata which in their turn have been lifted up and exposed to like conditions and have served, together with the formations already exposed, to furnish the new ma- terial for still later deposits. These strata have been laid down in vary- ing thicknesses but otherwise are somewhat like the leaves of a book with only the upturned edges accessible at the surface while their mass in general is largely overlaid by later deposits. 4. Mantle Rocks, which are the. more or less superficial deposits of disintegrated indurated formations produced by the destructive action of the atmosphere, of water and of ice, and which either remain a de- composed mass over the parent rock or have been transported by vari- ous agencies to other localities where they remain a surface deposit of soil and subsoil, comparatively loose and unconsolidated. 162. Historical Geology. — The study of geology has occupied the attention of many able and eminent men for many years, and many sec- tions of the earth have been studied in considerable detail. From the studies of conditions as they now exist, including the arrangement and characteristics of the strata, from the geological conditions now under process of development, and from numerous data too extensive to men- tion, conclusions have been drawn as to various conditions of the past, which, if summarized, will give the engineer a concrete idea of the man- ner of the growth of the continent, and will assist him in comprehending many local hydro-geological conditions which are less readily under- stood if examined as isolated and independent problems. The extent of certain geological deposits, the physical conditions that obtain therein, and the modifications of concomitant hydrographical conditions that result therefrom are in this manner more readily understood and ap- preciated. The geological deposits of greatest interest to the hydraulic engineer are those of sedimentary and glacial origin, for among these deposits are those which are of greatest importance as containing waters Historical Geology. 355 available as supplies, and those deposits which from their absorptive qualities most greatly influence the flow of streams both from absorbing, retaining and supplying waters under favorable hydrological condition. The hydrological character of the earlier rocks is not usually such as to render them available for water supplies, except through their cracks and fissures, which may be of local importance. The absence of absorp- tive qualities is, however, frequently of equal importance hydrologically on account of its important influence on runoff. 163. Chronological Order of Geological Time — Division of Strata. — From the earliest time the agencies now at work in the disintegration and rearrangement of geological deposits have been active in a similar manner but intensified at times by more extreme conditions of tempera- ture and atmospheric activity. The entire time since scientific observa- tions of geological conditions first began has occupied a comparatively few years, and the observed changes during that entire period have been limited but have served to indicate in no indefinite way the greater changes that have occurred in the past. Geological history as deter- mined from the strata involves geological activities of millions of years and the changes which have succeeded each other have often been wide- spread and fundamental. The chronological classification of the rock masses has therefore been based on the more radical changes which have resulted in : ( 1 ) the changed character of the strata themselves, and (2) the markedly dif- ferent characteristics in the life existing at the time of formation. During all these periods changes more or less complete were taking- place in the relative elevations of the rock surfaces both by erosion and by disatrophic movements, to both of which are due the contour and limi- tations of the existence of the consequent later strata. It is important to note that in many cases the deposits of different periods shade into each other through transition deposits more or less indeterminate, while in other cases the lines of demarcation are more obvious and the changes in character more complete. The following list includes the most important divisions of geological time, arranged in chronological order, the earliest in time occupy the base of the column and the remainder occur as they would in their na- tural or normal positions. 2 In no location is the above geological section complete but from the occurrence of these strata at various locations the sequence of forma- tion has been determined. Chamberlain and Salisbury Geology, Vol. 2, p. 160. 356 Geology. Fig. 213 is a geological map of the United States, showing the gen- eral formations so far as they are known to occur at the surface. From these outcroppings the strata clip in general in the direction of the later deposits, sinking beneath the surface under the more recent formations, and can be reached at points below the surface of more recent strata only by deep excavations or by the drill. Excavations made on the out- crops of geological deposits will in general uncover only formations of a still earlier age. Cenozoic Present \ „ , „. . , '. Quarternarv Pleistocene ( Pliocene ^ Miocene Oligocene Eocene Tertiary Mesozoic Paleozoic Upper Cretaceous Lower Cretaceous Jurassic Triassic Permian Coal Measures — Pennsylvanian Sub-carboniferous — Mississippian Devonian Silurian Ordovician Cambrian Carboniferous Proterozoic Keweenawan Animikean Huronian Archeozoic Archean Algonkian Pre Cambrian 164. The Precambrian Rocks. — At the beginning of the formation of the present sedimentary strata, the eafly Archean and Algonkian land areas were probably quite limited in extent, in comparison with the present exposed continental areas. The approximate boundaries, as far as known, and within the present area of North America, are shown in Fig. 214A. The entire area, deep below the present surface, is supposed to be underlaid by Archean rocks of unknown thickness, or by some other base rock on which rests the later sedimentary deposits. Ages before the formation of the present sedimentary deposits, the same processes had resulted in sedimentary deposits which, from the lapse of time and by the action of heat, pressure and other agencies, have been so changed and metamorphosed as to give many of them character- istics quite similar to the earlier Archean formations. Surface Formations in United States. 357 358 Geology. The earliest Archean deposits are the Laurentian rocks, consisting of granites, syenites, and allied rocks. Of a later origin are the Algonkian deposits, which consist of crystalline magnesium limestone, quartzite, slates and schists of the Huronian period, which contain the iron ores of Minnesota, Wisconsin and Michigan. The later Algonkian rocks of the Keweenawan period, consist of sedimentary rocks, sandstones, con- glomerates, and shales, with eruptive rocks containing the copper de- posits of the Lake Superior region. These rocks are flexed, folded, tilted and metamorphosed, showing evidences of upheaval and depression of the earth's crust of great mag- nitude and extent. With the exception of the eruptive rocks, most of the Algonkian rocks show evidence of sedimentary origin, indicating their derivation from a still more remote source, and that they are not themselves a portion of the original crust of the earth. Subsequent to the formation of the Archean and Algonkian deposits, and during the periods of the formation of the earlier sedimentary rocks, the central part of North America, including the Great Lake region, was occupied by an interior sea, the depth and extent of which fluctuated repeatedly. The rise in sea level with respect to the neighboring lands at certain times, is believed to have been due largely to the fact that the lands exposed to the disintegrating and denuding forces of the atmos- phere and of running water, were being reduced to lowlands, while the rock waste thus derived from them was being deposited in the sea, partly filling the basins. The water thus displaced rose, and even though the actual change of level was slight, it was sufficient to cause the sea to extend far over the lands on account of their greatly reduced elevations. These changes in the relation of land and sea were also doubtlessly caused by warpings and dislocations of the earth's crust. It is clear that many such warpings have occurred, for strata which must at the time of their deposition have been essentially horizontal and con- tinuous on the sea floor are now found widely scattered over the lands, and in a great variety of warped and folded forms. The reasons for these deformations can not be told with certainty. Gravity or the tendency of the earth's mass to settle towards its center, has probably caused the sinking of certain excessively loaded sections of the ocean floor which might have been less firmly supported from beneath than in other locali- ties. It is also possible that the cooling of the earth has caused con- traction, which has resulted in the outer portions accommodating them- selves to the shrinking nucleus by warping or wrinkling. Some of the changes that probably took place in the extent of land iv. Geological Periods. 359 Fig. 214. — Hypothetical Maps of Possible Relations of Land and Sea in Nortli America at Various Geological Periods (see page 358). 360 Geology. North America during the formation of the sedimentary strata are in- dicated by the hypothetical maps of Fig. 214." 165. The Upper Mississippi Valley. — To give a clearer idea of geo- logical growth, and of the geological structure of the earth, a more de- tailed study of some particular locality is desirable. This will enable the general features of geological structure to be more clearly under- stood than would be possible with the discussion of the larger area of the continent, or of the entire United States, where, from the multitude of details, the general principles are likely to be obscured. For this purpose, the Valley of the Upper Mississippi River has been selected, and in the study of the geological history of this territory it should be understood that it is but an example of quite similar con- ditions which have occurred in all portions of this country and of other lands. All lands have had a corresponding geological history, more or less varied, but in a general way controlled by similar laws, which have resulted in simi'ar general conditions, more or less modified in de- tail as the controlling factors have differed in their nature and extent. The Upper Mississippi Valley, together with much adjoining terri- tory, consisting of the Lake Michigan and Lake Superior basins and the valley of the Red River of the North, had a common geological origin and history, and, at a comparatively recent geological period, a common drainage system, all their waters emptying through various channels into the Mississippi River and thence into the Gulf of Mexico, until subsequent geological changes so modified the topography as to produce the present drainage systems. The territory here considered comprises the greater portion of Illi- nois, Iowa, Wisconsin and Minnesota, and a small portion of North- eastern Missouri and North-western Indiana, and embraces within its area much of the richest farming country of the United States, a country largely settled, and having numerous thriving and growing communities. In the north are forests of pine, and rich mines of iron and copper, while in the south are valuable deposits of bituminous coal and fire clay. De- posits of valuable building stone are found throughout its extent. It contains all the resources necessary for a rich and populous manufactur- ing and agricultural development. In order to show the details of geologic growths and their effects on the present geological and hydrographical conditions, a series of hypo- s See Bui. No. 11, Illinois Geological Survey; also Cleland's Geology, and Willis-Salisbury Outlines of Geological History. Upper Mississippi Valley. 361 Pig. 215.- — Hypothetical Maps and Sections of Possible Relations of Land and Sea in Upper Mississippi Valley during the Formation of Various Geo- logical Deposits (see page 3'60). 362 Geology. thetical maps has been prepared (see Fig. 215) showing the upper Mis- sissippi Valley at various periods in its geological history. 4 166. The Cambrian Period. — At the beginning of the Cambrian Period some diastrophic movements produced extended depressions of the earth's crust and caused the sea gradually to extend over the low in- terior of North America, expanding on all sides, until by the end of the period, all the central portion of the continent and most of the western and northern portions were submerged. An extensive highland belt (The Appalachian Uplift) separated this interior sea from the Atlantic on the east and long discontinuous mountain belts in the far west and northwest, separated it from the Pacific. On the north a great V- shaped land area in Canada (The Laurentian Outcrop), formed at that time the main part of the land of the North American continent. Two highlands, outliers of the Laurentian land, apparently escaped submer- gence : one in the Adirondack region of northern New York, and the other in the highlands of northern Wisconsin. Around their subsiding borders were spread out in late Cambrian times extensive deposits of sand. From the Wisconsin highland region, the sand reached south- ward on the sea floor well into Illinois, and now constitutes the Potsdam sandstone formation. 5 During this age the principal part of the upper Mississippi Valley (Fig. 215A) was under the sea, which throughout Wisconsin was com- paratively shallow and contained many quartzite islands of the Huronian formation, which yet rear their heads above the Potsdam outcrop. This Potsdam deposit consists mostly of sandstone derived from the broken quartz grains of the decomposed granites and allied rocks. These de- posits, close to the Archean land, consist of coarse quartzose sand rock, very open, porous, and free from the iron, lime and clay, which, in the higher strata, are found associated with it. The Cambrian Sea held in its depths some of the earliest forms of animal life. Myriads 'of small shellfish, the remains of which may be seen in many of the Potsdam out- crops, inhabited its waters. Although commonly spoken of as a single geological stratum, the Pots- dam is by no means homogeneous in texture throughout. During its formation a vast period of time elapsed, very many disturbances oc- curred, and the circumstances of deposition of the different portions of the stratum varied greatly. Those variations were almost or quite as great as those that marked the changes to subsequent geological ages. The evidence of this, in portions of Wisconsin, is so marked that ■* See The Hydro-Geology of the Upper Mississippi Valley, by Daniel W. Mead. 5 Bulletin 11, Illinois Geological Survey. Upper Mississippi Valley. 363 Professor T. C. Chamberlain has classed the Potsdam strata of Central and Eastern Wisconsin in the following subdivisions : Sub-Divisions of Potsdam Deposit. Thickness Feet. Sandstone ( Madison ) 35 Limestone shale and sandstone (Mendota) 60 Sandstone, calcareous 155 Bluish shale, calcareous 80 Sandstone, slightly calcareous 160 Very coarse sandstone, non-calcareous 280 Total 770 The thicknesses given are subject to wide variation. As a rule they thin out quite rapidly in Wisconsin, northward from Madison, and in- crease in thickness to the southward into Illinois. Professor W. H. Winchell notes a somewhat similar classification in Minnesota. In a deep well drilled in East Minneapolis he found the following series of Potsdam rocks. 6 Section of Artesian Well, East Minneapolis. Thickness Feet. Sand (Drift) 42 Blue limestone, Trenton 28 White sandstone, St. Peter's 164 Red limestone, Lower Magnesian 102 Gray limestone, Lower Magnesian 16 Potsdam: White limestone, Jordan 116 Blue shale, St. Lawrence limestone 128 White sandstone, Desbach 82 Blue shale ' 170 Sandy limestone 9 White sandstone 130 Sandy marl, Hinkley 8 White sandstone 79 Red marl 57 Red sandstone 290 1,069 Total 1,421 Although the classification into these sub-divisions is warranted by well-defined beds around Madison, Wisconsin, in eastern Wisconsin and in Minnesota, yet, owing to the thinning out or disappearance of these strata or by the multiplication of sub-divisions, the local variations are so great that in many places it is impossible to classify the strata found, under any general classification except the general name, Potsdam ; for the limits of this formation, as a whole, are well and clearly defined. e See Geology of Minnesota, Vol. II, p. 279. Hydrology — 24 364 Geology. As indicated in the foregoing tables, the Potsdam varies greatly in its character throughout its extent, not only from shale and limestone to sandstone, but also in the character of the sandstone, which is mostly Mc. 1I6. — Outcrops of Various Indurated Formations in the Upper Mississippi Valley, Drift Mantle Removed (see page 3G5). fine-grained, but becomes coarse-grained in its lower strata, and passes into a conglomerate near its margin, the shore of the ancient Archean land. As may be understood from its physical character, it readily transmits the water which it receives at its outcrop, either from rains or The Ordbvician Period. 365 from the numerous streams which flow over its exposed surface, the ex- tent of which may be judged from the maps. The outcrops of the Pots- dam occupy about 14,000 square miles in central Wisconsin, extending in a crescent-shaped tract around the Archean outcrop. (Fig- 216, page 364.) Below the later sedimentary deposits it occupies most of the area of the Upper Mississippi Valley and furnishes the source of thou- sands of private and public water supplies. 167. The Ordovician Period. — During the Ordovician period the in- terior sea continued to expand beyond its limits in the Cambrian period through local and temporary oscillations of its floor, and its shores kept changing their outline. In northern Illinois, a change from sandy sedi- ments to sandy limestones, and finally to pure, fine-grained limestone occurred as the period progressed, and indicates that the surrounding land areas suffered great reduction under the destructive actions, ero- sion and transportation, so that during the middle and late Ordovician period, the waters of the interior sea were no longer clouded by river- borne sediment, and the deposits made were limited almost wholly to shells, corals, and other organic remains. The early Ordovician sedi- ments are the Lower Magnesian limestone and the St. Peter sandstone. Above them is the Trenton limestone, containing an abundance of fossils which indicate that the water was relatively clear, shallow, and rather warm. (Fig. 214 B, page 359.) In the Upper Mississippi Valley two of these deposits are of consid- erable hydrological importance : the Lower Magnesian or Oneota Lime- stone and the St. Peter Sandstone. The Lower Magnesian is a dolomitic limestone, coarse, irregular in stratification, often inter-stratified with shale or sandstone layers and limestone breccia, which last, occurring in clusters or heaps, often gives the upper surface a billowy appearance and causes it to vary greatly in thickness. The variation in thickness seems to be more marked in Wisconsin than elsewhere. Although undoubtedly cracked and fissured to some extent, it seems to be in general free from these disturbances and to offer a quite uniform and homogeneous mass to prevent the upward passage of the waters con- tained in the Potsdam stratum below it. This stratum is found from 65 to 260 feet thick through Wisconsin and is from 105 feet to 170 feet thick in northern Illinois. It seems to thicken quite rapidly to the south- ward, and is found to be 490 feet thick at Joliet, 500 feet thick at Streator, and 811 feet thick at Rock Island. A flow of water, which may be derived from the underlying Potsdam sandstone, is sometimes, found in the softer portions of this stratum. 366 Geology. Over the Lower Magnesian limestone in the Upper Mississippi Valley lies a remarkably uniform quartzose sandstone. It is uniform in ma- terial and thickness, and quite covers all the irregularities in the surface of the underlying limestone, except at some points in Wisconsin where it is entirely pinched out and the Trenton limestone lies directly on the Lower Magnesian limestone. The average thickness of the St. Peter sandstone throughout the territory under discussion is probably about 150 feet, although in Wisconsin Chamberlain estimates its average thickness as only about 80 feet. This deposit is believed to have been formed in a shallow sea by the decomposition of the Archean and Potsdam rocks. The hypothetical condition of the Upper Missis- sippi Valley during the formation of the deposit is shown in Fig. 215B, page 361. No fossils have been found in this rock, and its formation marked an epoch probably unfavorable to the existence of life. This stratum has an outcrop of about 2,000 square miles in Wiscon- sin, and also crops out at several points in Illinois along a line of up- heaval which passes southwesterly from Stephenson County to the vicin- ity of La Salle, bringing the St. Peter to the surface along the Rock River at Oregon and Grand Detour, and along the Illinois River from La Salle to Ottawa. The Lower Magnesian limestone is also brought to the surface at Utica by this uplift. The St. Peter sandstone is an important water-bearing stratum, although its outcrop is so low that the pressure of its water is usually much less than the water of the Potsdam. Although apparently no life existed in this region during the forma- tion of the St. Peter sandstone, yet conditions favorable to the exist- ence of life again returned, accompanied by geographic changes in the relation between the sea and the land, and extensive beds of limestone were again deposited. These constituted the- limestones of the Trenton group, which may be divided into various substrata more or less distinct in character. Of these the Galena limestone is, perhaps, the best known, but for the purpose of this discussion the Trenton may be considered as a whole, inasmuch as its general character is approximately uniform. This deposit through its cracks, fissures and channels furnishes water in limited quantities for domestic use. Toward the close of the Ordovician period, the Trenton limestone deposit was buried by a great sheet of mud over 100 feet in thickness, which has since been consolidated into the Hudson River or Cincinnati shale. By the time this formation was deposited the interior sea had begun to shrink, and the surrounding land to emerge, exposing broad coastal plains, from which and across which, the sediment was washed into the sea. The Silurian Period. 367 Geographic changes of great extent now occurred. Intense deforma- tions in eastern New York added to the width of the Appalachian moun- tain belt, while in the Mississippi valley region there was a very exten- sive emergence of land, with, however, little or no deformation of the rocks. The interior sea shrank to smaller proportions and marine life became seriously restricted. These parallel changes of the geography and the fauna are the reasons for separating the Ordovician from the succeeding Silurian period. 1 68. The Silurian Period. — With the changes that occurred at the end of the Ordovician Period most of the interior of the continent be- came dry land, but as the Silurian period advanced, the inter-continen- tial sea once more encroached upon a part of the interior of the con- tinent. It expanded over Illinois and Michigan and southwest toward Arkansas and Missouri, where it was presumably bordered by a land area. (See Fig. 214C.) In this interior sea a great limestone forma- tion outcrops continuously for more than 1,000 miles from central New York to northeastern Iowa and is widely exposed about the Great Lakes. It takes its name from the Falls of Niagara, for which the hard lime- stone is chiefly responsible. Like most limestone the Niagara Lime- stone was originally an organic deposit, made up of an accumulation of calcareous skeletons and shells of marine animals, worked over by the waves and currents, and ground to a fine calcareous mud. One of its distinctive features is its wealth in fossils remains. Evidently, the in- terior sea was nearly free from river-borne sediment in most places ; hence, it is believed that the surrounding lands were low and the rivers sluggish. (Fig. 215 C, page 361.) 169. The Devonian Period. — At the close of the Silurian period, the emergence of large portions of the interior of the continent greatly re- stricted the inland sea. Subsidance of the land and expansions of the sea were renewed in the Devonian period. (Fig". 214 D, page 359.) By me middle of this period, the most of the upper Mississippi and the Ohio River were again below the sea. The Devonian occurs as surface rock in northwestern Indiana, where it is almost concealed by glacial drift. There is a Devonian outcrop near Milwaukee, Wisconsin, and near Rock Island, Illinois. During the greater part of the Devonian time most of Wisconsin and northern Illinois was above sea level, and may have been a part of a large land surface stretching south toward the Ozark uplift, of Missouri. Near the close of the Devonian period, when the sea again occupied much of this region, sands were sifted down into the open joints of the 368 Geology. lower strata, and with it the fossil remains that marked the Devonian period in those states. 170. Carboniferous Period. — The strata of the coal measures are the youngest bedrock of the upper Mississippi valley, and are therefore the highest rock formation wherever they exist in this region. The Pennsylvania system lies at the north margin of the great Illinois coal measures, and in most cases is found in isolated patches which lie north of the margin of the continuous coal area measures, and are the rem- nants of a continuous series which once extended farther to the north. The coal measures consist primarily of shales and secondarily, of sandstones. Among the shales beds of coal and black seams of carboni- ferous matter are common. The unexposed or fresher exposed shales are usually blue or drab. They occur in thick massive beds but soon weather into thin friable laminae and become lighter in color. Sandstone often consists of thick massive beds, but sometimes occurs as thin layers interbedded with the shales. The base upon which the coal measure rests is very regular in some places ; at the south, it con- sists of Devonian limestone, while in the north, coal measures rest on the Niagara limestone. The probable extent of land and sea during this age is illustrated by Fig. 215 D, page 361, which shows the further recession of the sea and the consequent limitation of the strata then under process of formation. This age ushered in an epoch of life very different from any which had preceded it. Its deposits were comparatively local in character, and although they have in a general way been correlated, yet there is a greater variation in these strata than in those of any preceding de- posits. Especially is this true in those of the coal measures proper. These deposits seem to have been made in shallow seas, lakes or swamps of limited extent, rather than in a broad and deep sea such as those in which most of the preceding deposits had been formed. Hence, great local variations are observable and the strata have commonly a much more limited geographic extent. This age witnessed the formation of extensive beds of limestone, sandstone, shales and coal. 171. Sedimentary Deposits of Later Periods. — The periods briefly outlined above, in order to furnish some conception of geologic growth, were succeeded in other parts of the country by numerous other more recent sedimentary deposits outlined in Sec. 163. These may be of great importance in the study of the hydrological phenomena of the locality in which they occur. Their consideration in detail is not con- sidered of importance in this chapter as the entire subject of geology Geological Structure. 369 must be taken up in much greater detail than is possible in one volume in order to give sufficient knowledge for its intelligent application to the work of the engineer. 172. General Characteristics of the Strata. — It should be under- stood that lines of exact demarkation seldom exist between the various strata. One stratum usually passes gradually into another. Changes in the controlling influence which modify the deposition were usually not radical and they obtained only gradually. Thus, in passing from sandstone to limestone, the upper strata of the sandstone will usually be found somewhat calcareous, and the lower strata of the limestone some- what silicious. A like condition applies to the character of the stratum throughout its geographic extent. The conditions at one point may have been such as to favor the formation of limestone deposits, while those at a point more or less remote may, during the same period, have been favorable to the formation of shale. We thus find widely different strata belong- ing to the same age. Hence, a stratum may within a short distance merge from a sandstone into a limestone, from a limestone into a shale, or the reverse, or from a coarse-grained stone to a fine and more im- pervious one. Or a stratum may even have been entirely lost by reason of a local elevation which raised the rock at that point above the sea level, thus preventing deposits, or by the existence of local ocean cur- rents which might accomplish the same result. The more widespread the conditions controlling deposition, the more uniform is the character of the resulting stratum throughout its extent. The character of the rock deposit which we may encounter in drilling is often highly problem- atic, and it is only by an extended examination of facts as they have been found to exist, and by their proper correlation, that we may ar- rive at conclusions as to what we must expect in new and untried locali- ties. The farther the point in question lies from those where the char- acter of the sub-strata is known," the greater is the uncertainty respect- ing it. 173. Modifications of the Strata. — The original extent of the vari- ous sedimentary strata of the Upper Mississippi Valley was much greater than the present geological map of the region would indicate. Hundreds of feet in thickness have been disintegrated and eroded by drainage waters. The Hudson River shale, while now encircling Cen- tral Wisconsin and Central Northern Illinois as a narrow belt (Fig. 216, page 364), undoubtedly once covered a much greater area, as did the strata of the Niagara group. The section through Elk Mound shows Hydrology — 24 370 Geology. J9AJU S-/OU///J J3AI& XOJ 9 s p ' Is : J9Al,H U?C£/ uos-tpuw JJAI& U/QUODS-/A1 -/3AI& uis-uoy^/AA UO £•//?&{*/ . Salisbury, 3 vols., 1906, Henry Holt and Co., Vol. I, Geological Processes and Their Results. Vols. II and III, Earth History. College Geology, T. C. Chamberlain and R. D. Salisbury, 1900, Henry Holt and Company. Text Booh of Geology, L. V. Pirsson and Chas. Schuchert 2 Parts, 1915, John Wiley & Sons, New York. Part I, Physical Geology, Part II, Historical Geology. Elements of Geology, Joseph LeConte, Revised by H. L. Fairchild, 5th Ed., 1910, D. Appleton & Co., New York. Geology, Physical and Historical , H. F. Cleland, 1916, American Book Company, New York. Introduction to Historical Geology, W. J. Miller, 1916, J. Van Xostrand Co.. New York. Causal Geology, E. H. L. Schwarz, 1910, Blackie & Son, London. Outlines of Geologic History with Special Reference to North America. Bailey Willis, R. D. Salisbury, 1910, The University of Chicago Press. Physiographic Processes, J. W. Powell, Am. Book Co., 1896. Hydro-Geology of Upper Mississippi Valley, D. W. Mead, Jour. Assoc. Eng. Sac, Vol. 13, 1894. ECONOMIC AND FIELD GEOLOGT. Economic Geology, H. Ries, 1911, The MacMillan Co., New York. Engineering Geology, H. Ries and T. L. Watson, 1914, John Wiley & Sons Co., New York. Geology for Engineers, R. F. Sorsbie, 1911, Chas. Griffin & Co., London. Field Geology, F. H. Lakes, 1916, McGraw-Hill Book Co., New York. f> See The Austin Dam, T. U. Taylor, Water Supply Paper No. 40, 1900, U. S. Geological Survey; also Report on the Dam and Water Power Development at Austin, Texas, Daniel W. Mead, 1917, City of Austin, Publishers. io Rock Grouting and Caisson Sinking for Hales Bar Dam, Eng. News, Vol. 70, 1913, pp. 949 and 1039; see also Eng. Rec. Vol. 59, 1909, p. 470 and Vol. 63, 1911, p. 641. Literature. 389 Outlines of Field Geology, A. Geikie, 5th Ed., 1912, MacMillan Co., New York. Catskill Water Supply of New York, Lazarus White, John Wiley & Sons, 1913. Dam and Reservoir Foundations, C. M. Saville. Eng. News, Vol. 75, 1916, p. 1229. The Austin Dam, T. U. Taylor, U. S. G. S. Water Supply Paper 40, 1900. Report on Dam and Water Power Development at Austin, Texas, D. W. Mead, 1917, City of Austin, Publisher. Rock Grouting and Caisson Sinking at Hales Bar Dam, Eng. News, Vol. 70, 1913, Eng. Rec, Vol. 59, 1909, and Vol. 63, 1911. Tennessee River Between Brown's Island and Florence, Alabama, Document 1202, House of Representatives, 64th Congress, 1st Session. See also Reports of United States Geological Survey and the reports of the Geological Surveys of the various States. CHAPTER XV GROUND WATERS 183. The Importance of Ground Waters. — Most private and in- stitutional water supplies, and many supplies for small towns and even for cities of considerable size such as Madison, Wisconsin ; Rockford, Illinois ; Memphis, Tennessee ; Austin, Texas, and Savannah, Georgia are secured from underground sources. This use of ground waters for private and public supplies is due to the apparent and in most cases the actual freedom of such waters from the grosser forms of pollution and to the fact that in general more satisfactory small supplies and often more satisfactory supplies of considerable size can be obtained more readily and by less expensive means from ground than from surface waters. Ground waters commonly need no treatment to make them suitable for domestic and manufacturing uses. Such sources have also been extensively utilized for irrigation purposes and occasionally for small water powers. The low water flow of streams is due entirely to ground waters, and conditions favorable to the storage of ground water and its delivery to the stream are essential to the maintenance of dry weather flow. In humid countries, streams that uniformly dry up in summer are those on whose drainage area there is little or no ground water storage. The conditions which give rise to underground waters and the con- ditions favorable to their flow are also of importance in many hydraulic works. Conditions favorable to ground waters may add to the difficul- ties and expense of the construction of foundation work and may per- mit flows under dams and reservoir embankments and from reservoirs, canals and ditches, and thus perhaps endanger the works or at least re- sult in a loss of water which may prove more or less serious. Ground waters also have important relations to agriculture, and a knowledge of these relations and of the flows of water in soil is indis- pensable to the engineer in the proper design of drainage and irrigation works. 184. Origin and Occurrence of Ground Water. — All ground waters are derived directly or indirectly from the rainfall. The nature of the surface on which the rain falls has an important influence on its disposal. Such conditions vary from inclined impervious rock or clay surfaces, from which practically all rainfall rapidly drains away, through all va- Origin and Occurrence of Ground Water. 391 rieties of texture, porosity and surface covering, to horizontal, pervious beds of sand and gravel which under normal conditions imbibe all, rain water received on their surface. In general, however ; i. A part of the rainfall is evaporated directly into the atmosphere. 2. A part flows directly into drainage channels as surface flow or runoff, and 3. A part seeps into the soil, subsoil and underlying strata, finally reaching an outlet in springs, streams, lakes or in the ocean. On account of the saturated condition of the atmosphere during rain- storms, evaporation is at such times small in amount compared with that which takes place from the soil between rainstorms through capil- larity and the action of vegetable life. The evaporation from soil has been discussed in Sec. 74, and Fig. 84, page 139, which illustrates evapor- ation under different conditions. The evaporation was calculated by deducting from the total rainfall the amounts of seepage waters col- lected. Fig. 228 is a direct comparison of the seepage and rainfall in these same experiments and gives some data on the amount of water which passes permanently into the ground water when the soils are well drained by underlying pervious substrata, although in the cases noted the depths of soil were not sufficient to eliminate entirely the surface evaporation losses. (See also Table 7, page 144.) In addition to the water received directly from the rainfall it should be noted that under some circumstances the ground waters are also aug- mented by streams which seep into and sometimes entirely disappear in their porous beds (Fig. 232), and by the seepage of irrigation waters into the soil. All of the materials of the earth's crust, whether loose mantle deposits or consolidated rocks, are capable of absorbing water both on account of their porous structure and by reason of cracks and fissures. The capacity for absorption varies with the porosity of the strata which in turn varies with the size and shape of the particles of which they are composed and the manner in which they are deposited. Fine material may have as great porosity as coarse material, that is the ratio of total pore space to volume of the material may be the same in two cases al- though the actual sizes of the interstices may be different. Different samples of the various geological deposits vary widely in porosity. The results of certain determinations of porosity measured by the percentage (in volume) of water absorbed are given in Tab!e 38. 392 Ground Waters. o r?.2 4.0 %3.6 ^ 3.4 $3.2 % 3 ° % e.s Q; 2.6 ^ /.a S /.6 &'■* $ /.o o.e ^ 0.2 o JTMAMJJASOND Q -Ffofhamstec i Expei -/me nfs /e 7/-/i 7.90 -is / *) \, 1 w ei / V \ J{ \ s ft t / \ \ \l .«? ^ \ y ft \ d \ \ it V l % V, ,\ / V J r M A A7 J J AS O N D 3.6 3.4 3.2 3.0 2.8 2.6 24 e.e eo / 8 / 6 / 4 /.e /.o 0.8 0.6 0.4 o.e o 4^ 4.0 3.8 3.6 3.4 3.2 3.0 2.8 2.6 2.4 e.2 eo /.8 /.6 /.4 /.2 /O 0.8 0.6 0.4 0.2 O B - Greaves Experiment/ /860-/873 K \ A \ \ \ A r / n \ ,^ fo * T ' / ?\ \ A $ *' \ V /^ \*r -d / / 1 X V ^ > A \ \ 1 I \ i k 8 N $1 V M V V / V- ->-- ^ v7 F /*7 A M ^ ^ /? s O /V Z) A Z? " Geneva Exp. A Z333-/887 /\ L ?/ \ « A \ \ \ - K \ — cs u sy A 5 A i i / x j R \ 4 / \\ 7 V / v ■A' y, •Yl w Q ; r v 7" !V- V' n* 5 i .' > Kj \r \ ^ r v 3 S ft Atf- -w- rd' 'H v $ r J r Af A M J J A 3 O A/ D Fig. 228. — Results of Experiments on Soils under Various Surface Percolation of Rainfall into Various Conditions (see page 391). Origin and Occurrence of Ground Water. 393 TABLE 38. Approximate Quantity of Water Which toill be Absorbed by Soils and Rocks. Volume of Water Absorbed Material per 100 of Material Sandy Soil i 45.4 Chalk Soil i 49.5 Clay i 50-52.7 Loam i 45.1-G0.1 Garden Earth i 69.0 Coarse Sand i 39.4 Peat Subsoil i 84.0 Sand 30-40 Sandstone 5-20 Limestone and Dolomite 1-8 Chalk 6-27 Granite 03.-.S The ground water in general saturates the strata to a depth at which the materials are so consolidated by the superincumbent weight that cracks, fissures and pores are eliminated. This depth is commonly es- timated at from 6,ooo to 10,000 feet but practically the ground water is confined to the upper 5,000 feet in sedimentary rocks and to about 500 feet in crystalline rocks. The strata are in general permanently sat- urated to the sea level near the coast and to other higher levels in the interior of the country, practically fixed by the surface of lakes, swamps or streams. From these more or less fixed water levels the water table or ground water surface slopes upward as it recedes from the point of discharge. (See Fig. 229, A.) The saturation of the strata is not always complete. Many mines in both sedimentary and crystalline rocks are dry even far below water levels, and sandstones free from water have been encountered in deep wells. 2 The water levels of lakes and streams are in general dependent upon the ground water level. (Fig. 229, B.) If lakes or ponds are fed by streams they may seep into lower adjacent ground waters (Fig. 229, C). This condition, however, is unusual except where such bodies of water are artificial, under which conditions the lower adjacent ground water may cause considerable losses from the stored water. Occasion- ally reservoirs or lakes may exist above the general ground water plain without serious loss on account of the local underlying impervious strata ( Fig. 229, D), and in some cases more than one water table may obtain due to local geological structure. (Fig. 229, E.) Water is en- 1 From Geology of Soils and Substrata, H. B. Woodward, Pub. by Edward Arnold, London, 1912. - W. L. Fuller, Economic Geology, Vol. 1, page 565. 394 Ground Waters. *4. ■Section of Long fs/and Showing' f/eva/ion of Ground Wafer o .;.- ; Sand and Grove/ ■'■•:o .. ' -°- "':©; Q. Lake Maintained by Ground Wafer Sancf and Grave/ £50 r C. Lake Maintained by Stream _, Wafer Seeping info Surrounding So//. ^300 C ^eoo \/oo o Lake on Impervious Materia/ Over/ying Unsaturated Sand ,Sha//oyv Wel/s — -, (Pond ///, Sea Leve /-////. Mam Water Tai>/e 77^771 7~/-/~/777~/7 O./ fy?//e = . . // / Perched Wafer Tab/e Ma/nfa/ned by fmpervious Under/ying Strata Fig. 229. — Occurrence of Ground Water under Various Conditions of Mantle Deposits. Movement of Ground Water. 395 countered in small quantities in crystalline rocks 3 and shales 4 but is found more abundantly in limestones, sandstones, and in the sands and gravels of glacial deposits and river valleys. 185. Movements of Ground Water. — The water absorbed by the soil passes downward, due to gravity, until it joins and modifies the sur- face elevation of the permanent ground water, it then seeps toward lower levels through paths of least resistance. The flow of water through the strata is governed by the same factors that control hydrau- lic flow in canals, pipes or other passages. (Fig. 230, A.) The size of the pores or passages in the water bearing material, the length of travel (/), the relative height of the source and point of discharge (h), and the quantity of water available result in the establishment of an hydraulic gradient ( A B) and a resultant flow that remains constant only as long as the factors remain unchanged. When the ground water at the source rises (B to B,) due to seepage from rainfall or other sources, the head (h,), the hydraulic gradient (A B, ), and the flow are increased. If through lack of supply the ground water falls (B to B,,), the head (h n ) is decreased, and the hydraulic gradient (A B,,) and the quantity of flow are reduced. In the same manner the flow of ground water is affected by the elevation of the surface of the body of water into which it flows. The sudden rise of a river surface (from A A to C C, Fig. 230, B) due to floods will frequently not only immediately reduce the ground water flow from that produced by the normal gradient (AB) but will often temporarily stop the flow and sometimes reverse it. In such cases the river water seeps back into the pervious banks of the stream (CD) until a new gradient (CB) is established. The tide influences the flow into the sea in the same manner and necessarily af- fects the elevation of the water of wells which draw their supply from the same stratum. (Fig. 230, C.) In the same way the discharge of springs and flowing wells will increase during the passage of low baro- metric storm areas as demonstrated by King (Fig. 230, D). 5 The ground water surface or hydraulic gradient has a slope propor- tional to the resistance of the soil or rock texture to the flow and to the amount of water seeping toward the outlet. In gravels and other coarse s Underground Waters in Crystalline Rocks, F. G. Clapp. Eng. Rec, Vol. 60, 1909, p. 525. . 4 Underground "Waters in Slate and Shale, F. G. Clapp, Eng. Rec, Vol. 59, 1909, p. 751. 5 See 19th Annual Report U. S. Geological Survey, 1897-98, Part 2, Princi- ples and Conditions of the Movements of Ground Water, F. H. King; also Water Supply Paper No. 67. p. 70. 396 Ground Waters. X? l/ar/af/on of flow and Gradient with Wafer Supply B Variarfion of Flow and Gradient yvifh River Heights ■JulyS Ja/ y /0 . July II Ju/y/2 C effect of Tides on Fl evafion of Ground Wafer { l/eatch) Wednesday Thursday Friday 12 2 4 6 8 10 M 2 4 6 8 /O 12 2 4 6 8 /0 M 2 4' 6 8 10 12 2 4 6 8 /OM 31.0 30.5 30.0 29.5 23.0 O effect of Baromefnc Pressure on Discharge of Spnnas and Wells, ftfing) Fig. 230. — Gradients and Elevations of Ground Water as Affected by Various Conditions (see page 395). 1 A ^ ux-" \ \ *r ZP ^ / s/ V i v V s / k, y/ \ y~ A y / > \ v. ) f \j \J \ \ -/e. riaj M 7 f >ie Vet D 1 C 'St an ft f Jit 'V> \ \f\ V J \ V r-s S Pff Movement of Ground Water. 397 materials the water moves freely and the inclination of the water sur- face is comparatively small, while in materials of close texture the gradient must be considerable to produce movement. In their flow from the line of the drainage area to the stream the Diagram Showing Levef of Ground Wafer During Spring Reriocf and ifs fSffecf on Var/ous Surface Condifions. Diagram Shoyving Leref of Ground Wafer During Summer Period and Change of Various Surface Condifions. Pig. 231. — Normal Conditions of Ground Water during Wet and Dry Periods (see page 398). ■Scale of 'Miles o 10 20 JO Fig. 232. — Deltas of Disappearing Streams (see page 399). 398 Ground Waters. seepage waters commonly encounter differing degrees of resistance due to changes in porosity and size of soil grains even in the same stratum, hence the gradient is seldom constant except for short distances where uniform conditions prevail. Due to irregularities in surface and sub- surface conditions the hydraulic gradient recedes from or approaches Gra v/ty Spring c "AY ■;M^v£- ^ Spring due to Fautf or Fissure. Spr/ng from fissured flock Spring from Cavernous f-fock Submarrne Spring from Pervious Stratum fnferm/ttant Spring Fig. 233. — Geological Conditions which give Rise to Various Classes of Springs (see page 399). the surface and gives rise to various phenomena illustrated in Fig. 231. When the water plain or hydraulic gradient reaches or passes above the surface the ground water causes springs, streams, lakes or swamps (Fig. 231, A), which during dry weather may become partially or en- tirely dried up when the water plain falls below the surface at the locality where it formerly existed. (Fig. 231, B.) In some cases the Movement of Ground Water. 399 ground water by reason of other and lower outlets may fall below the beds or adjacent streams in which case the streamflow will be decreased by seepage into its bed and banks. This is often the case in Eastern rivers when sudden floods raise the stream surface above the ground water level as noted above and is a phenomenon of common occurrence in the West where desert streams fed from the mountains flow into plains having small rainfall and low ground water. In some cases under such circumstances the streams are entirely lost by sinking into the plains after leaving their mountain channels. (See Fig. 232.) Fig. 234. — The Thousand Springs, Snake River Canyon, Idaho. In many cases ground waters seep through pervious deposits which lie below comparatively impervious beds on which they produce an upward hydrostatic pressure due to the head at their source less the head lost by resistance of flow. Where such waters encounter cracks, fis- sures or wells through the overlying deposits, they rise through such openings and if the hydrostatic pressure is sufficient may appear at the surface as springs or flowing wells. 186. Springs. — When the hydraulic gradient of the underground water passes above the surface at any point (Fig. 231, A), and when the water bearing strata also reaches or connects with the surface, springs are formed. (Fig. 233.) Springs are sometimes produced by surface outcrops of impervious strata overlaid by pervious water bearing de- 400 Ground Waters. SaBTO/v 3f>GjNaL « Fig. 235 A. — Fault Zone near Austin, Texas (see page 401). posits (Fig. 233, A), or by the occurrence of surface outlets from cracked, fissured or cavernous rocks. (Fig. 233, C.) The open texture of the lava rock on the side of the Snake River Canyon in Idaho has given rise to the series of springs shown in Fig. 234. Sometimes the hydrostatic pressure raises the underground waters to the surface Springs. 401 through cracks, fissures or fault lines (Fig. 233, B). Springs of large capacity are often found along fault lines where the faults intersect deep lying water bearing rocks. Such a condition is found near Austin, Texas (Fig. 235), where an extensive fault zone exists. Numerous /Qusf/n Cha/k Buc/erCShoa/Oh S ■ Limestone ' Feet r/000 fagteford Sha/es Dei Rio C/ays ■Fort Worth Limes tone Traris k&ak formation Miles Fig. 235 B. — Geological Section Through Fault Zone near Austin, Texas.* Fig. 23G. — Barton Springs from Fault, Austin, Texas, springs are found in this vicinity the largest of which is Barton Springs on the south side of the Colorado River (Fig. 236). This spring flows through fissures in the rock bed and banks of Barton Creek and has an average flow of about fifteen cubic feet per second and will probably be utilized as a water supply for the City of Austin. The cracked, fissured and pulverized rock of one of these faults pass- *Geologic Atlas of the U. S., Austin Folio, R. T. Hill and T. W. Vaughan, 19.02 Hydrology — 26 402 Ground Waters. ing under the bed of the river at the dam site above Austin was un- doubtedly the cause of the failure of the dam at that place in 1900 and of much of the trouble in rebuilding that structure. f_= Approximate Strike Lines Soft =£T= and Cavernous Strata Ponds and S/nks in Limestone Strata iOOOO 300O0 40000 £0000 Distance in /^eef SLTCrtOiV AB Fig. 237. — Map and Section near Sheffield, Albama, Showing Conditions which give Rise to Disappearing Streams and to Springs. Springs often result from the flow of water through the passages in cavernous rock which outcrop at or above the surface. (Fig. 233, D.) In general, the formation of caverns by solution is limited to the rock mass above the outlet water level although the rock structure may occa- sionally produce lower lines of flow and consequent cavernous condi- g Austin Dam, T. U. Taylor, Water Supply Paper No. 40, 1900, also Report on the Dam and Water Power Development at Austin, Texas, Daniel W. Mead, City of Austin, Publisher. Springs 403 tions far below the outlet water levels. In other cases cavernous condi- tions may have been produced in the rocks of valleys that have later been filled with glacial, lacustrian or fluvial deposits, or disastrophic movements may have lowered the cavernous rock far below the present water plains. Numerous springs of this class occur in most limestone regions. The exposed beds of soluble limestone in Northern Alabama near Sheffield (Fig. 237) have developed many cavernous channels. Into one of these, Pond Creek, draining about 35 miles of surface area, disappears. The Fig. 238. — Outlet Creek from Tuscumbia Springs near Sheffield Alabama (see Fig. 237). development of cavernous conditions in another stratum gives rise to Tuscumbia Springs (Fig. 238), one of the largest springs in Northern Alabama. Springs from cavernous stone are sometimes intermittent on account of peculiar formations. In general, such results are produced by the formation of a collecting cavern within the rock together with a syphon outlet channel (Fig. 233, F) in which case the water begins to flow when the cavern fills to the top of the outlet channel and ceases to flow when the supply in the reservoir or cavern is exhausted, which action is re- peated as the reservoir alternately fills and empties. Frequently in- clined pervious strata are exposed by the erosion of the overlying rock by streams, lakes or the ocean and numerous surface and submarine springs result. (Fig. 233, E., page 398.) 404 Ground Waters. 187. Artesian Conditions. — Early wells drilled into the deep under- lying strata in the Province of Artois, France, produced flowing waters at the surface. Similar conditions have since been discovered in num- erous parts of the world and such conditions and the wells which de- velop them have been called "artesian" from the place of their first de- velopment. In order to produce flow at the surface the hydraulic gradient of the underlying water bearing deposits must pass above the surface, other- wise the water will simply rise in the well to the local elevation of the gradient. (Fig. 239.) The term artesian is, however, commonly applied m— — 11 m r'T,'- -'' -^ M - ? -- 'Crc/sfalline Rock ~ 11-11 = 11=11=11=. n= ( , •4j, - m - Fig. 239. — Section Showing Artesian Conditions and Relations of Flowing and Non-Flowing Wells to Hydraulic Gradient and Surface Elevation (Fuller). to both rising and flowing wells and also to springs occurring through cracks, fissures and faults. (Fig. 233, B.) The leading prerequisite conditions on which artesian flows depend are given by Chamberlain 7 as follows : 1. A pervious stratum to permit the entrance and the passage of the water. 2. A practically water-tight bed below to prevent the escape of the water downward. 3. A like impervious bed above to prevent escape upward, for the water, being under pressure from the fountain head, would otherwise find relief in that direction. 4. An inclination of these beds, so that the edge at which the waters enter will be higher than the surface at the well. ' The Requisite and Qualifying Conditions of Artesian Wells, T. C. Cham- berlain, Fifth Annual Report U. S. Geological Survey, 1884, p. 131. Artesian Conditions. 405 5. A suitable exposure of the edge of the porous stratum, so that it may take in a sufficient supply of water. 6. An adequate rainfall to furnish this supply. 7. An absence of any (easy) escape for the water at a lower level than the surface of the well. For large flows the waterbearing material must be coarse and porous or the thickness must be great and the outcrop must be of large area and the rainfall ample. Fig. 240. — Map Showing Principal Artesian Areas of the United States. The artesian wells of Denver formerly provided a large surface flow in the spring and early summer when the snow was melting from the foothills, but these wells decreased or ceased to flow during the dry periods of the summer. The numerous artesian wells in the Upper Mississippi Valley (for geological section see C D, Fig. 217, page 370), especially those derived from the Potsdam Sandstone show no seasonal variations in flow due to the extended outcrop of the Potsdam in North- ern Wisconsin (about 14,000 square miles, see Fig. 216, page 364). The principal artesian areas in the United States are shown in Fig. 240. Geological sections which show the conditions that give rise to such wells are given in Fig. 241 for the Dakotas (A), along the Atlantic Plains (B), in Eastern Texas (C), and in the San Joaquin Valley (D). Numerous local artesian conditions are developed in the drift in Wis- consin, Illinois, Indiana and other localities, and many minor artesian 406 Ground Waters. 4O00 7TZ fJ- Cross Section through South Da KoTa Artesian Basin. ( Darton.) • J Atlantic Ocean | 400 \ ZOO, ^^Wmwm ^§^m^mmMm \$^m^$$. v xxxx MTOn> G- [deal ' •Section Showing Artesian Conditions at Ft. Worth, Texas. I tzooo Brewster — iMerrill r-Tu/are , Baird— \ I I if arret -, r Visalia D-Ideal*5ectior7,3anJoaquin ]/alley through Tulare Lake. (GrunsHy) Fig. 241. — Geological Sections Showing Various Artesian Conditions in the United States (see page 405). Underflow of Streams. 407 areas occur locally in various points of the United States, especially in the lower lands of river valleys. 8 188. The Underflow of Streams. — Many streams flow over beds of sand, gravels or other pervious materials such as lacustrine deposits and Sec f/o/-? ar 6> c Fig. 242. — Map and Section Showing Ground Water Conditions in the Gila and Salt River Valleys. After Lee. (See page 408.) those which have been deposited in older and deeper valleys by glacial action, by the work of former streams or by the present streams where conditions have changed their work from degradation to aggradation. These deposits are frequently very extensive and sometimes afford op- s Water Supplies of Wisconsin, S. Weidman and A. R. Schultz, Bui. No. 35, Wis. Geol. and Nat. Hist. Survey, 1915, p. 88. The Water Resources of Illinois, Frank Leverett, 17th An. Report U. S. Geological Survey, 1895-96, Pt. 2, p. 78. Water Resources of Indiana and Ohio, Frank Leverett, 18th An. Report U. S. Geological Survey, 1896-97, Pt. 4, p. 480. 408 Ground Waters. portunities for securing abundant water supplies at points far distant from the stream channel. The underflow of the Salt and Gila River Valleys in Arizona (Fig. 242) is extensively used for the irrigation of lands both inside and outside the United States reclamation project boundaries, some of these wells furnishing (by means of pumps) sup- plies of four cubic feet per second (Fig. 243). Many supplies of cities Fig. 243. — One of the Wells of the Southwestern Cotton Company in the Gila Valley. Four Cubic feet per Second Pumped from Ground Water. are taken from similar sources. The water supply of Wichita, Kansas, is derived from the underflow of the Arkansas River and provides an adequate amount of water for that city when the river bed is dry and the ground water surface of the underflow is drawn down several feet below the river bed. (Fig. 244.) In many cases where the old stream valleys are filled with sands and gravels, the presence or absence of streamflow is simply a question of the elevation of the general ground water gradient above or below the stream bed. In other cases, when the present beds are more or less impervious, the streamflow and the underflow are independent both in character and direction of flow. Temperature of Ground Water. 409 189. Temperature of Ground Waters. — It has been shown (see Fig. 14, page 48) that the temperature of the earth below the surface is not subject to as great a range of temperatures as air or surface waters. In consequence of this even the higher ground waters are comparativly cool in summer and warm in winter. There is also a considerable in- crease in temperature from the surface downward amounting in gen- eral to about one degree for each 50 to 100 feet. The U. S. Geological Survey measured the temperature in the deep well at Wheeling, West Virginia with the results shown in Table 39. Fig. 244. — Sand Bed of the Arkansas River at Wichita, Kansas, during Low Water (see page 408). TABLE 39. nderground Temperatures at Different Depths in the Well at Wheeling, West Yir ginia. Temperature Temperature Depth Feet Fahr. Degrees Depth Feet Fahr. Degrees 100 51.30 2,990 86.60 1,350 68.75 3,125 88.40 1,591 70.15 3,232 89.75 1,592 70.25 3,375 92.10 1,745 71.70 3,482 93.60 1,835 72.80 3,625 96.10 2,125 76.25 3,730 97.55 2,236 77.40 3,875 100.05 2,375 79.20 3,980 101.75 2,436 80.50 4,125 104.10 2,625 82.20 4,200 105.55 2,740 83.65 4,575 108.40 2,875 85.5 4,462 110.15 410 Ground Waters. These temperatures may be compared with those of the deep well near Berlin, Germany, which is 4170 feet in depth and has a surface temperature of 47.8° and a bottom temperature of 118.6 , and with the well at Leipsig, Germany, 5,740 feet deep with temperatures at the top TABLE 40. Temperatures of Deep Well Waters. Location of Well Rockford, 111 Galena, 111 Oak Park, 111 Ellendale, N. D. ... Redfield, S. D Huron, S. D Yankton, S. D Jamestown, N. D. St. Augustine, Fla. . Alamosa, Colo Canon City, Colo.. .. Denver, Colo Denver, Colo Guntersville, Ala. . . Arkansas City. Ark. Loyalton, Cal Santa Clara. Cal. . . Oglethorpe, Ga Keokuk, la Richfield, Kan Louisville, Ky Elkton, Md New Orleans, La. . , Alpena, Mich Winona, Minn Scranton, Miss Louisiana, Mo Miles City, Mont. . . . Omaha, Neb Sierra Valley, Nev. . Longport, N. J Ashland, Pa Charleston, S. C. ... Knoxville, Tenn. . . Ft. Worth, Tex Galveston, Tex Reedville, Va N. Yakima, Wash. . . Green Bay, Wis. . . . Tem- pera- Depth ture De- of Well grees F. 1320 to 1996 60 1509 49 2780 64 1087 67 960 68 863 60 600 62 1576 75 1400 86 1000 75 1600 90 500 50 350 56 1006 60 552 72 1000 130 600 60 490 62 2000 65 370 66 1900 57 490 45 1200 68 650 52 478 54 774 74 1275 64 456 57 1065 62 . 1132 Hot 803 66 1830 54 1970 99.5 2100 57 3250 140 1365 84 680 78 650 71 950 53 Reference Eng. News, Vol. 21, 1889, p. 326, 1 -Eng. News, Vol. 21, 1889. Eng. News, Vol. 27, 1892. '1 1-U. S. G. S. Water Supply Paper 51 U. S. G. S. Water Supply Paper 61. Temperature of Ground Water. 411 and bottom of 51. 9 and 135.5 ° respectively. On account of these con- ditions deep well waters are usually much warmer than the shallower ground waters, as shown in Table 40. In certain regions thermal springs are found which are sometimes of boiling temperatures. Some of these derive their temperature from the great depths to which the seepage waters have previously percolated through fissures. In other cases the waters are heated by chemical ac- tion, while in volcanic regions waters are heated to high temperatures at comparatively shallow depths by the presence of uncooled lava. There are about 3,000 springs of this latter class in Yellowstone National Park. TABLE 41. Qualities 0/ Water Collected During a Rainstorm, at Rothamsted, England.^ (Parts per million) Total Solids Carbon in Organic Matter Nitrogen as Time of Collection Organic Matter Am- monia Nitrites and Nitrates Total Ni- trogen Chlor- ine 3:00 P.M. 4:30 P.M. 40.8 29.4 0.93 0.62 0.18 0.19 1.07 0.37 0.18 0.13 1.43 0.69 1.0 0.8 190. The Qualities of Ground Water. — No water is found in a state of chemical purity in nature. The rain falling through the atmosphere takes up various floating matters and absorbs various gases from the air. Its quality improves in the later part of the storm after the air has been partially cleansed by the earlier rainfall. (See Table 41.) When it reaches the ground, the rain water as it runs over the sur- face dissolves, erodes and carries away in solution and in suspension some of the various materials with which it comes in contact. In this way the streams receive the washings from farm yards and fields and carry away silt, sand and organic matter to the rivers and the sea. In the same manner the water also carries similar matter into cracks and fissures of the rock, but as it seeps into the soil and sand, the coarser materials in suspension are left on the surface and only the finer organic and mineral matter and the matter in solution are carried into the ground. As the water flows through the soil and underlying forma- 9 Journal of the Royal Agricultural Society, 1847, p. 257. 412 Ground Waters. tions, the matter in suspension is rapidly removed if the strata are fine material, but the moving water constantly adds to its burden of matter in solution and becomes more highly mineralized the more soluble the 47 Fig. 245. — Average Mineral Content in Parts per Million of Surface and Rock Wells in Wisconsin. After Weidman and Schultz. material of the strata with which it comes in contact and the longer and farther it flows. Water from the cracks and fissures of the comparatively insoluble crystalline rocks contains only a small amount of matter in solution and is termed "soft water." The mantle and sedimentary rocks contain much soluble matter and the waters from such deposits are more highly mineralized the farther they are found from their source. As in gen- eral the deeper rocks in any section appear at the surface and absorb the Qualities of Ground Water. 413 rainfall at a greater distance from that section, the deep waters are in general more highly mineralized than those from lesser depths. The progressive increase in mineral content of the ground water in propor- tion to the depth and travel is shown in the map (Fig. 245) and section (Fig. 246) of Wisconsin, and in Table 42 which includes also the deeper waters of Iowa. 10 In Iowa deep wells are defined as those more than 700 feet in depth. -J500 Fig. 246. — Geological Section through Wisconsin and Average Mineral Content of Surface and Rock Wells. After Weidman and Schultz. TABLE 42. Showing the Relation 0/ Depth to Mineralisation of Underground Water in Wisconsin and Iowa. Approximate Depth of Underground District Water or Thick- Average Mineral Content ness of the Water- in Parts per Million bearing Strata 100 to 200 Feet... Surface Deposit Wells 121 400 to 800 Feet... Rock Wells 135 Surface Deposit Wells 224 800 to 1600 Feet.. . Rock Wells 216 Southwestern Wisconsin . . Surface Deposit Wells 330 Rock Wells 339 Northeastern Iowa 1600 to 2000 Feet... Shallow Wells 388 Deep Wells 351 Central Iowa About 3000 Feet. . . Shallow Wells 873 Deep Wells 1759 South Central and South- western Iowa About 4000 Feet.. . Shallow Wells 1587 Deep Wells 3657 10 Water Supplies of Wisconsin, by Samuel W. Weidman and A. R. Schultz. 414 Ground Waters. The character of the mineral content of underground waters depends entirely upon the chemical character of the strata through which they flow. (See Table 43.) The waters of the Potsdam Sandstone of the Upper Mississippi Valley (see Table 44) are more largely charged with the bicarbonates of lime, soda and magnesia, with minor quantities of TABLE 43. Analysis of Residues of Various Spring Waters in the Upper Mississippi Valley, Grams per U. S. Gallon. Compound Elgin, 111. 'Zoman Spring Cook Co., 111. Glen Flora Spring St. Croix, Wis. Mineral Spring a Wauke- sha, Wis. Hygeia Spring Owatonna, Minn. Vichy Spring .69 .28 Sodium Sulphate. 1.75 1.85 .52 .45 .71 .46 .18 0.45 .05 .79 '1.89 .34 52.41 4.04 4.63 .21 19.23 Magnesium Bicarbonate . . 11.09 7.25 8.40 2.50 Calcium Bicarbonate 15.57 11.19 16.37 Calcium Carbonate 9.57 Calcium Sulphate 1.62 .01 | 3.04 .71 1.43 Ferrous Bicarbonate .54 Ferrous Carbonate .50 } •» .11 .15 .91 j .49 .27 1.43 Alumina Carbonate Silica .10 1 . 70 Free Carbon Dioxide 4.34 Total grains per Gallon 15.76 36.31 20.56 37.50 85.02 a Spring from Potsdam Strata. sodium chloride and occasionally with many other salts. The waters from limestone regions commonly contain carbonates of lime and mag- nesia with various other salts. On account of the mineral content of ground waters, the consequent flow of streams is much harder during low water periods than during high water when the flow is derived largely from surface runoff. In the desert regions of the West the soils contain greater proportions of the alkaline salts which are detrimental to vegetation. Waters from such strata, when they rise to the surface or when they stand on the sur- face and evaporate, leave behind an alkaline residue which prevents the growth of vegetation and spoils the land for agricultural purposes until Qualities of Ground Water. 415 it is properly drained and the deposited salts are dissolved and carried away by the proper application of irrigation waters. Waters from underground sources which in general are more highly mineralized than surface waters are as a rule free from the grosser forms of pollution often found in surface streams. The soil and mantle TABLE 44. Mineral Character of Waters from Sandstones at Various Places in the Upper Mississippi Valley, Grams per U. 8. Gallon. Compound Jersey- ville, 111. Water Works Well Mon- mouth , 111. Water Works Well Dekalb, 111. Water Works AVell Rock- ford, 111. Water Works AVell Mad- ison, AVis. AVater AVorks AVell Sheboy- gan, AVis. Public AVell Potassiun Sulphate Sodium Sulphate Potassium Chloride 10.. SO 5.05 4.86 23.45 [ 1.13 } - .50 .36 .24 .2!) 14.48 Sodium Chloride Magnesium Bicarbonate .... Magnesium Chloride 85.93 Trace 15.53 9.61 .27 Trace 12.80 .29 Trace 12.89 306.04 14.07 6.47 . 17 54.01 Calcium Chloride 27 . 82 Calcium Bicai'bonate Calcium Sulphate Ferrous Bicarbonate Alumina 6.84 16.91 .11 .06 .78 15.82 4.70 .24 .10 1.04 8.39 13.17 15.24 i :-; . m 160.^3 |- . 69 .70a 17.40 .08 .14 .58 .82 28.72 .21 Trace 1 .OH 30.25 .50 13 Silica .47 Sodium Bicarbonate .33b Totals 141.51 73.89 5S0 -'4 * Organic. b Composed of chlorides of lithium, bromide of sodium and phosphates of line, with trace of soda, sulphate of baryta and bicarborate of soda. deposits undoubtedly have a purifying effect on polluted waters both by straining action and by the activity of nitrifying organisms in the upper soil. Nevertheless, the waters of many shallow wells are frequently grossly polluted by seepage from nearby vaults, cesspools and barnyards (Fig. 247) , and often deep wells are polluted in the same manner by im- proper casing through the mantle deposits. Springs and deep wells are also sometimes polluted by the passage of organic matter through open and cavernous formations (Fig. 248). Such pollution is of a most dan- gerous character because its existence is unseen and unrealized, and the clear and sparkling waters seldom give apparent evidence of their dangerous condition. 416 Ground Waters. 191. Velocities and Quantities of Ground Water Flow. — In many places where ancient river valleys are filled with great deposits of sand and gravel there are extensive ground waters from which large supplies are sometimes obtained. (See Fig. 243.) The general public and Fig. 247. — Pollution of Wells from Surface Drainage of Streets and Seepage from Vaults (see page 415). sometimes engineers, in making estimates of the quantities that can be obtained from such sources, are misled by the large volume of water present in these deposits. The movement of such ground waters under their normal gradient is very low (see Table 45), and to secure a large Fig. 248. — Pollution of Spring from Surface and Subsurface Drainage ( see page 415). quantity of water from wells, filters, galleries, etc., a considerable de- pression must be created in the ground water plain in order to produce the comparatively large head necessary to increase the velocity and in- duce the desired flow. In the spring of 1918 such a source was proposed as a water supply for a large irrigation project in a Western state. During the spring" and fall water is available from a stream which, however, becomes drv Flow of Ground Water. 417 Cb g -2 © o © a do© '7 Hrlrl P _3 © © © • 2 2 g = oddootV^c?.co $> - -,-t th ih . , — ^ — ' o -r^r-r-r m.ooo re -t. a a a ^ £j • > c> £! o ■Wco " 'l " rf< ■* -fl 1-H m a--ti ... r r r o • * • • o a o o ■M a- 1 i^S m mxn%i<6<£mm r r J^uixnmm £i k* - -_-.-«.,.,. ..---.-~ a - r k aiaiaJDQaJaJos* p^ 02 ai 02 od ^£ d ddeddcJd H .® H ddddeS g^ ai sd cc 02 ai 02 oq 02 "£ ■£ ■£ a! 1 a: ad m w r-lH J3 tjDpt3D^P^<). • ■/! ESS ^ i/imm . Ml o .a "2 u u u •- s- u u u e* t CU t, g M OOOCOOO - C E.£.S •aj t. *— ' *o y - 5aoaoo HHH 0' 3:3 ^ =: hS 02 KKKKKKKCCOKmE-" ^ oco cccoooo-t* G eg O 00 CMC fCOm-1-OO tofl ci 10 1" c.ncc-tif-fi-cc.:i:u-o * o -t- 1 6 66 c . c . c : c . t °. t ^ rl iH r-1 CC CC I- 01 CC t- M CI MHrti-i "^ o a — id +^2 — o 2 -CI • _ _, _ ■ OH -P® . • (N 1 • 1- 1- 1- 00 -f 00 CC l" 00 CI CI CI . . . . . ■ . > +i ■3 0,02 ; ■a ! a . : -| :§ :■§'! : -a a T a ■ r/> . 9 05 : a '=0^9 ' w cd *i«7 — - 02 C5 +J " •iSK'Sti r-q B (< > >■ Hi ra pc^aC .c5-M a «eS a? a cs ci a eS i' -j s-i O ci •- •- . d a . oa-s-t 50 «! U C-i - > > > > w w • fe > a >. >. >> ,£Ky = = = 7: y: w M O 0J .a — • ^ ~ C3 C3 cj ■3 1.2 B - ra to •>-->,, ^ "o "0 *o »—< z: ti ^ C cj ^^^ be M bB fcc si O +j cJ — ~ ~ .- a a a a «« "3 a '0 g 3 S*S S=~5 XT. VI M K OOOO Q -K< :is ^ < : >cie — «_ Hydrology — 27 418 Ground Waters. for about six months during the principal irrigation season, and during this time water to the amount of 750 cubic feet per second would have to be obtained, if at all, from the ground water which in the upper val- ley is contained in coarse sand and gravels several miles in width and several hundred feet in depth, and from which large supplies are ob- tained from wells. The underflow at the outlet of the valley passes through the section shown in Fig. 249, with an area above the rock bed and below the stream bed of 50,000 square feet. Five thousand square feet of this is fine sand and silt, and 45,000 square feet is coarse sand Fiu. 249. — Underflow Section of a Western River. and gravel. The ground water above this section has a slope toward the outlet of nine feet per mile. The project involved an expenditure of about $2,000,000 and promised a large profit if the ground water supply was dependable. The engineer of the project reported that a sufficient supply could be obtained from this source. Was he correct? An in- vestigation of the probable flow in this cross section as shown, and on the assumption of the section being entirely filled with sands and gravels of various degrees of coarseness and with other ground water slopes, will furnish a point to the following discussion and show how important the subject of ground water flow may become under certain conditions. In investigating the flow of water through sand, experiments have been made on materials which could be examined, weighed, measured, and the porosity of which could be determined by various methods which the experimenter applied. Even under such conditions it has been found that the accurate determination of porosity and the effective Flow of Ground Water. 419 size of the material are attained only by careful manipulation, and that where crude methods are applied to such measurements very discordant results are obtained. In the formulas derived from the experiments of Hazen 11 and Slichter, 1 - an "effective size" of sand or soil grains, expressed in milli- meters, is used to define the comparative coarseness of the material ; but each experimenter determined this by a different method, and there is no known basis of comparison between them. These form- ulas are inapplicable unless "effective size" of the material and other factors are determined in the same manner and with the same degree of care and skill as in the case of the original experiments, and even then they will apply only to conditions of uniformity and kind of ma- terial used in the original experiments and which can be found only under experimental conditions. 13 The general principles that underlie the flow of ground water through porous soils are as follows : The velocity of flow will i. Increase directly with the head or difference in elevations between the water at the inlet and outlet of the column of soil. 2. Decrease directly with the length of travel through the column of soil considered. 3. Increase rapidly with the size of the pores of the water bearing material. 4. Increase rapidly with the porosity or percentage of voids in the water bearing material. 5. Increase with the temperature of the flowing water. Darcy, 14 who made the first attempt to investigate this subject, pointed 11 Annual Report Mass. State Board of Health, 1892, p. 541. Some Physical Properties of Sands and Gravels with Special Reference to Their Use in Fil- tration, Allen Hazen. Note — Mr. Hazen has called attention to the purpose of these investigations and cautioned against the use of his formula under conditions foreign to those from which it was derived. See A. S. C. E., Vol. 73, p. 199. v Nineteenth Annual Report U. S. Geological Survey, 1897-98, Pt. 2, C. S. Slichter, Theoretical Investigations of the Motion of Ground Water; also Water Supply Paper No. 67, C. S. Slichter, The Motion of Underground Water. is When the problem of the engineer is such that the size of grains and character of the material can be determined (as in flow through filter sands) he should refer to the original discussion of this subject as a basis for his calculations for information concerning methods of determining porosity and effective size. "Les fontanies publiques de la ville de Dijoin H. Darcy, 1856, Paris. 420 Ground Waters. out that the velocity of flow through soil is directly proportional to the head and inversely proportional to the length of flow ; that is h (1) v = k — 1 Where v = Velocity of flow (in feet per minute) h = Head acting on the soil section (in feet) 1 = Length of the column or soil section (in feet) - k = A factor of flow to be determined experimentally for each ma- terial Slichter's formula for estimating the flow of water through a column of sand is as follows : hd a (2) q = 0.2012 fdK in which q = Quantity of water transmitted by the column per minute h = The head producing the flow (in feet) a = Area of the cross section of the sand bed ( in square feet ) 1 = Length of travel of the water d = The effective diameter or effective size of the sand grains n = A viscosity coefficient (which decreases rapidly with an in- crease in temperature) K = Porosity coefficient (varying with porosities of from 20 to 47 per cent) The part of the expression varying with the character of the soil may be represented by a coefficient or transmission constant, k, when Equa- tion 2 becomes ha (3) q = k — 1 which is essentially the same as the formula of Darcy. As has previously been noted, the formulas of. the type of Equation 2 for the flow of water through sand, etc., are all dependent upon the ac- curate determination of porosity and effective size of the porous medium. This effective size is dependent on the nature of about ten per cent, of the finest material, and there is no method uniformly applicable by which this effective size can be accurately determined for all classes of material. Even the porosity of a fine material cannot be determined without great care, for this factor depends not only on the size and shape of the grains but on the method of packing as well, and a removal of samples from a natural bed will alter their arrangement and may affect the porosity. In estimating the flow of ground waters both the porosity of the ma- terial and the effective size of the grains must be assumed, or at best, de- termined only at a few points, while the porous beds may extend for Flow of Ground Water. 421 miles and actually vary in both factors every few feet throughout their entire extent. The answer to the problem must therefore be found by estimating" what probably would occur if the porous medium had a cer- tain porosity and a certain definite character, and on this basis calculat- ing limiting values which will afford a much better guide to the engineer than an assumption of flow based on the desire of the investigator to secure a certain quantity of water for a certain purpose. It should be understood that any calculations of the velocity of flow of ground water can be regarded only as a rough approximation which will undoubtedly vary widely from the truth as developed by actual de- termination of flow by experiment or from the measurement of flow into wells, infiltration galleries, etc., and in consequence large factors of safety must be allowed in making estimates which are to serve as bases for investments. From Equation 3 it will be seen that the flow of water through fine materials where capillary attraction is effective is found to vary directly with the slope ; then the flow for a slope of io c /o is one-tenth of the amount of flow under unity slope (see Table 48) , while for slopes of 1 % it is .01, for .\ c /c it is .001, and for a slope of a foot per mile orr- it is .00189 of the flow for unity slope. This does not apply to coarse gravels when the velocity of flow varies more nearly with \/h. Slichter has found that the flow of water will increase rapidly with the temperature, and that the flow at various temperatures compared with the flow at the temperature of 50 F., taken at unity, will vary as shown in Table 46. He also finds that the flow of water rapidly in- TABLE 4G. Effect of Tevi per ■xture on Flow of Water Compared toith Floiv at 50° F. = 1.00 Temperature Fahrenheit 32" 35" 40" 50°' 55" G0° 65" 70° 75° 80° 90° Relative Flow .74 .78 .85 1.00 1.0S 1.16 1.25 1.34 1.42 1.51 1.70 creases with the porosity, and that the flow for various porosities com- pared with the flow for a porosity of 32^ taken as unity will vary as shown in Table 47. TABLE 47. Effect of Varying Percentages of Porosity on Flow of Water Compared ivith Porosity at .12% = 1.00 Porosity or Percent of Voids 30 32 34 36 38 40 Relative Flow .81 1.00 1.22 1.47 1.76 2.09 422 Ground Waters. Slichter has also determined that the flow of water through various classes of material will vary under conditions of 50 F. temperatures, 32% porosity and with unity gradient, approximately as given in Table 48. TABLE 48. Transmission coefficient (k) or Velocity of Flow of Water with Unity Slope at ■50° F. and 32% Porosity in Various Soils. Silt .00012 .002 (In feet per minute) !3 Sand Fine From To Very Pine .003 .009 P"ine Medium .011 .07 .046 .26 Coarse .28 1.02 Gravel 1.1 28.0 The quantity of water flowing in a given section of material may be found by the expression ( 4 ) Q = vap in which Q = Cubic feet per minute v = Velocity determined as above porosity a = Area of cross section x 100 p = Porosity For example, determine the quantity of water flowing through 1000 square feet of fine gravel (of maximum coarseness) with a temperature of 60 ° Fahr., a porosity of .40 and a gradient of 20 feet per mile. The flow at unity gradient in such material is 28 feet per minute, and a gradi- ent of f , ■ = .00379 I hence the velocity of flow at this gradient will be .00379 times 28 = .106 feet per minute. For a temperature of 60 ° F. this will be increased by 16%, and for a porosity of .40 by 109% ; hence the actual velocity will equal .106 times 1.16 times 2.09 = .257 feet per minute. The flow area a p will equal 1000 square feet times .40 = 400, and the quantity of flow will equal .257 times 400 = 103 cubic feet per minute or 1.7 cubic feet per second. The opportunities for gross errors in such computations as are made above are obvious, and yet the extreme case which can reasonably be assumed will often correct false impressions of possible capacities which otherwise would lead to serious results. Where more detailed informa- tion is necessary, it may sometimes be secured by the actual measure- ir ' The transmission coefficient k is the flow that will take place in a column of the selected material of standard porosity (32 per cent) at standard tem- perature (50° Fahr.) and under unity slope, that is with a head (h) equal to the length of the column of material (I) which condition is found in a vertical column with the water surface standing at the surface of th2 material. Flow of Ground Water. 423 ments of ground water velocity as suggested by Slichter in 1902. 1G Prof. Slichter's method is to sink two or more wells into the underflow, separated in the direction of flow by a certain known distance. By in- troducing an electrolyte into the higher well and utilizing electrical means, the time of passage of the water containing the chemical can be ascertained by the deflection of an ammeter needle and the velocity of the underflow thus determined. It is to be noted that the velocity of the underflow in different parts of a section varies greatly in accordance with the materials, the porosities and the contour of the underground channel. (See Fig. 250.) Fig. 250. — Velocity of Ground Water at Various Points in the Section of the Narrows of the Mohave River. After Slichter. 192. Wells. — Wells are excavations from the surface into underlying deposits and are usually constructed for the purpose of obtaining under- ground water for various purposes. In general, the waters have to be raised by some form of pump but occasionally with artesian conditions the water will flow at the surface. A well is therefore an artificial out- let for ground water, and when pumping is begun the first effect is to lower the hydraulic gradient or level of the ground water in the immedi- ate vicinity of the well sufficiently to create the head necessary to pro- duce the desired flow. Wells in cracked, fissured and cavernous rocks (Fig. 251) depend on local conditions for their yield. These conditions can seldom be de- termined except by actual construction, although previous local experi- ence may furnish a valuable guide as to what may be expected in new construction. Successful wells in crystalline and limestone rocks must reach water bearing cracks or fissures and a failure to encounter such 10 Water Supply Paper No. 67, by C. S. Slichter, The Motion of Underground Water. Water Supply Paper No. 110, C. S. Slichter, Underflow Meter used in Measuring Movements of Underground Waters. 424 Ground Waters. conditions will result in dry wells (Fig. 251, A & B). Wells in clay deposits containing sand beds or pockets are subject to similar contin- gencies (Fig. 251, C). Sometimes adjacent wells may furnish supplies of water which differ widely in mineral content or in organic purity on account of quite different sources from which their supplies are de- rived. (Fig. 251, D.) >?. Dry and Wafer Searing Wef/s /n Crysfa///ne Rock 8. Dry and Wafer 3ecrr/nc? We//s in L /m esfone. C. Ory and Wafer 3ear/ny kYe/fs /'n C/ay Contc/n/na Sand and Gnare/ Beds. D. ffard trnef Soff Wafer from Adjacent We//s. Fig. 251. — Conditions Favorable and Adverse to Securing Satisfactory Wells. The quantity of water which may be secured from any well can in general be determined only by actual test. Such tests are usually made by pumping the well continuously for a considerable period ; but even then the effects of long dry periods on the supply can only be estimated. For small supplies such tests are quite satisfactory but for large sup- plies the ultimate results are more or less problematic. The principles of the flows of water in beds of sand and gravel of fairly uniform character are more readily determined. The principles of flows into wells are essentially the same as those for natural flow of ground water into streams or other natural outlets, and the continuous operation of the well tends to exhaust the ground water, to reduce its elevation in adjacent strata and gradually to increase the depth from which it has to be raised. As the water producing area created by the Wells. 425 construction of the well is comparatively small, the gradient necessary for the production of considerable supplies is correspondingly large. Turneaure 17 has shown that when a well is sunk through any water bearing sand stratum the flow will be given by Equation 5. (5) in which Q = Quantity of water in cubic feet per day r = The radius of the well in feet k = Transmission constant of material p = Porosity of the water bearing material h = Height of water above the base of the water bearing stratum y = Height of any point in the ground water plain above the bottom of the well at x distance from the well x = Distance of any point in the ground water plain from the center of the well loge x = Hyperbolic logarithm of x From this equation the slope of the cone of depression can be deter- mined. (Fig. 252, A.) When pumping first begins this area of depression will gradually widen and affect the ground water for some considerable distance in every direction, and its slope will be somewhat modified by the normal slope of the ground water and the direction of its flow. The continu- ous pumping of wells from superficial deposits will gradually reduce the ground water level at continually increasing distances from the well until, if the supply be sufficient, a new ground water gradient is es- tablished which will be maintained as long as the relations of supply and demand obtain. If the supply is practically inexhaustible, the cone of depression will finally assume a permanent form with a fixed circle of influence having a diameter x beyond which the ground water will not be lowered and the ordinate y will equal H. Under these conditions Equation 5 may be written 18 Trkp ( H + h ) ( h — h ) (0) Q = x log, — r From which it is apparent that the supply will be proportional both to H -\- h and to H — h, which has been found to be the case in many it Public Water Supplies, F .E. Turneaure and H. L. Russell, 2d Ed., 190S, p. 279. is Ibid, p. 213. 426 Ground Waters. actual tests. From this equation it is understood that for small de- pressions in the ground water level the quantity of water will vary al- most directly with the head but that for considerable depressions the increase in quantity is small. (Fig. 252, B.) In deep wells where the reduction in head even if considerable is usually small with relation to the total depth of the wells, the flow is al- most directly proportional to the reduction in head below the hydraulic gradient. (Fig. 253.) When, however, the diameter of the well is small in proportion to the Ground Leyet v: fte/af/re r/e/ct 0.2 0.4 0.6 0.8 /.C \> kaa .r Y 6 \ ■£• 0.8 X > <* /Q. Cone of Depression of Ground Water B. jRe/ot/on of Reduction of fteacf to r/e/ct of We//s Fig. 252. — Principles of the Hydraulics of Wells. flow, the friction in the casing will reduce the discharge and this effect must be taken into account in any estimate of the yield of wells. 10 The elevation of ground water in wells is subject to all the seasonal variations of supply together with the additional factor of demand created by its use. The waters rise and fall with the rainfall and the season (Fig. 254), and the depth of the well and the pumping appliances used must be adjusted to meet all such conditions. As noted, every well in active operation creates in the surrounding water bearing strata a cone of draft dependent upon the principles discussed and affects the ground water gradient for a greater or less distance from the well, in accordance with the demand for water and the pervious character of the strata. Where a single well is insufficient to supply the amount of water de- sired, and additional wells are constructed, they must for economical 10 See Public Water Supplies, F. E. Turneaure, page 287. Wells 427 20 40 60 80 /OO /BO /40 /60 /SO 200 220 240 260 280 300 r~/ow in 7~housarnds of Ga//ons per Day /3. f^/orv of We//s af ancf aSove Grounaf Leve/ Surface of Ground-^ eo 40 60 80 /OO /eo /■40 /60 /80 200 220 240 57a-/ C fl 'ecrd A >o r /or*f 1 jl K^-t ~xpe '-/me *r?fa / /= 'o/hf s. >sP 1 8/2/6 20 24 28 82 36 40 44 48 S2 S6 60 f^/orv in 7~r>OLisands of Ga/ions per ^ o y S. r~/or* of We/is 6e/or* Ground Level ( Determined by flumping-) Fig. 253. — Flow Measurements from Certain Australian Wells.* ♦Artesian System of Western Queensland, C. J. R. Williams, Proc. Inst. C. E , Vol. 159, p. 315, 1904-5. 428 Ground Waters. /9/3 Z9/-4 /9/S /9/6 s oNDjrrJA/*?ji/A 5 o/vDurnAnjjA 5 o /v dj rnArr Fig. 254. — Variations in the Elevation of Water Surface in Wells due to Rain- fall and Season. After Meinzer (see page 426). Grour-rc/ Lere/ Fig. 255. — Illustration of the Interference of Wells. reasons be constructed at sufficient distances from other wells so as not to interfere greatly with the cone of draft ; otherwise the capacity of the wells so constructed will be reduced (Fig. 255). It is usually impracti- cable to construct wells in such manner that no interference will occur and various practical considerations must furnish a basis for their Wells. 429 proper adjustment. Where flowing wells are developed in the artesian areas they often furnish a convenient and economical method of obtain- ing water supplies, especially when the flow is sufficient to meet the de- mand. A successful well of this kind in a thickly populated commun- itv, however, soon brings about the construction of similar wells and as the wells increase in number and the quantity of water obtained increases in volume, the hydraulic gradient is gradually reduced until the supply required is so great that the wells cease to flow and pumping appliances have to be introduced in order to obtain the necessary supplies. As the demand for water supply increases the hydraulic gradient is farther and farther reduced until finally the water has to be raised from a consid- erable depth and the necessary expense involved finally limits the de- mand. The hydraulic gradient then becomes essentially permanent if the quantity of water in the strata and the drainage area of its outcrop are sufficient to maintain it. LITERATURE GROUND WATER Some Physical Properties of Sands and Gravels, with Special Reference to Their Uses in Filtration, Allen Hazen, Annual Report State Board of Health, 1892. See also Trans. Am. Soc. C. E., Vol. 73, p. 199, 1911. Principles and Conditions of the Movements of Ground Waters, F. H. King, 19th Annual Report U. S. G. S., Pt. 2, 1897-8, p. 67. Theoretical Investigation of the Motion of Ground Water, C. S. Slichter, 19th •Annual Report U. S. G. S., Pt. 2, 1897-8, p. 295. See also Water Supply Paper No. 67, 1902. ' The Rate of Movement of Underground Water, C. S. Slichter, U. S. G. S. Water Supply Paper No. 140, 1905. Underground Water Resources of Long Island, N. Y., A. C. Veatch, C. S. Slichter and others, U. S. G. S. Professional Paper No. 44, 1906. The Underflow of the South Platte Valley, C. S. Slichter and H. G. Wolff, U. S. G. S. Water Supply Paper No. 184, 1906. The Underflow in Arkansas Valley in Western Kansas, C. S. Slichter, W. S. & Irrigation Paper No. 153, 1906. Underflow Tests in the Drainage Basin of Los Angeles River, Homer Hamlin, U. S. G. S. Water Supply Paper No. 112, 1905. Bibilographic Reviexo and Index of Papers Relating to Underground Waters published by the U. S. Geological Survey from JS79 to 190 h, M. L. Fuller, U. S. G. S. Water Supply Paper No. 120, 1905. Bibliographic Reviexo and Index of Underground Water Literature in 1905, Fuller, Clapp and Johnson, U. S. G. S. Water Supply Paper No. 163, 1906. Experiences had During the Last Twenty-five Years with Water Works having Underground Source of Sujoply, B. Salbach, Trans. Am. Soc. C. E., Vol. 30, p. 293, 1893. Water Resources of Illixwis, Frank Leverett, 17th Annual Report U. S. G. S., 1896-7, Pt. 4, p. 480. 430 Ground Waters. Preliminary Report on the Geology and Water Resources of Nebraska West of the One Hundred and Third Meridian, N. H. Darton, 19th Annual Report U..S. G. S., 1897-8, Pt. 4, p. 719. Geology and Underground Water Resources of the Central Great Plains, N. H. Darton, U. S. G. S. Professional Paper No. 32, 1905. Underground Water Investigations in United States, M. L. Fuller, Economic Geology and American Geologist, Vol. I, No. 6, June, 1906. This paper contains a number of references on the subject of ground water. The Underground Water Resources of Alabama, E. A. Smith, Geological Sur- vey of Alabama, Univ. of Alabama, 1907. A Preliminary Report on the Underground Water Supply of Central Florida, E. H. Sellards, Bulletin No. 1, Florida State Geological Survey, 1908. Public Water Supplies, Turneaure and Russell, Wiley and Sons, Pub., Chap. 7, p. 87, 1908. Underground Waters in Crystalline Rocks, F. G. Clapp, Eng. Rec. Vol. 60, p. 525, 1909. Underground Waters in Slate and Shale, F. G. Clapp, Eng. Rec, Vol. 59, p. 751, 1909. Groundwater Supply and Irrigation in the Rillito Valley, G. E. P. Smith, Bul- tin No. 64, Agr. Exp. Sta., Univ. of Arizona, 1910. Geology of Soils and Szibst7-ata, H. B. Woodward, Edw. Arnold, London, 1912. The Undergrounds Water Supply of West Central and West Florida, E. H. Sel- lards and Herman Gunter, 4th Annual Report Florida Geol. Survey, 1912, p. 81. Ground Waters as Sources of Public Water Supplies. Wm. S. Johnson, Jour. N. E. W. W. Asso., Dec. 1909. The Underground Waters of North Central Indiana, Stephen R. Capps, Water Supply Paper No. 254, U. S. G. S.. 1910. Underground Waters for Farm Use, Myron L. Fuller, Water Supply Paper No. 255, U. S. G. S., 1910. Wells as Sources of Supplementary Water Supplies, Myron L. Fuller, Eng. News, Sept. 12, 1912. Ground Water Supplies, Wm. S. Johnson, Jour. Boston Soc. C. E., May, 1915. Water Supplies of Wisconsin, S. Weidman and A. R. Schultz, Bui. No. 35, Wis. Geol. & Nat. Hist. Survey, 1915. Watei-works Handbook, Flinn, Weston and Bogert, Chap. 4, p. 73, McGraw- Hill Book Co., N. Y., 1916. Water Supply, William P. Mason, Chap. VIII, p. 373, Wiley and Sons, 1916. Qualitative Estimation of Ground Waters for Public Supplies, Myron L. Fuller, Jour. N. E. W. W. Assoc, June, 1913. Geology and Water Resources of Big Smoky, Clayton and Alkali Spring Val- leys, Nevada, O. E. Meinzer, U. S. G. S. Water Supply Paper No. 423, 1917. For references concerning seepage and percolation see literature for Chap- ter VI. ARTESIAX AND DEEP WELL WATERS Requisite and Qualifying Conditions of Artesian Wells. T. C. Chamberlain, 5th Annual Report U. S. G. S., 1884, p. 131. Flow of Artesian Wells and Their Mutual Interference, C. S. Slichter, 19th Annual Report U. S. G. S., p. 358, 1897-8. Literature. 43 1 Artesian Flows from Unconfined Sandy Strata, Myron L. Fuller, Eng. News, Mar. 30, 1905, p. 329. The Interference of Wells, Frederick G. Clapp, Eng. News, Vol. 62, p. 483, 1909. Basic Principles of Ground Water Collection, Charles B. Burdick, Am. W. W. Asso., June, 1913. Drilled Wells of the Triassic Area of the Connecticut Valley, W. H. C. Pynchon, W. S. & Irrig. Paper No. 110, p. 95, 1904. Spring System of the Decaturville Dome, Camden County, Missouri, E. M. Shepard, W. S. & Irrig. Paper No. 110, p. 113, 1904. Deep Borings in the United States, N. H. Darton, W. S. & Irrig. Paper No. 57, 1902, No. 61, 1902, and No. 149, 1905. Record of Deep Well Drilling for 190'/, M. L. Fuller, E. F. Lines and A. C. Veatch, U. S. G. S. Bui No. 264, 1905. Record of Deep Well Drilling for 1905, M. L. Fuller and S. Sanford, U. S. G. S. Bui. No. 268, 1906. Flowing Wells and Municipal Water Supplies in the Southern Portion of the Southern Peninsula of Michigan, Frank Leverett, W. S. and Irrig. Paper No. 182, 1906. The Underground Water Resources of Alabama. Eugene A. Smith, State Geolg- ist, Geol. Survey of Alabama, 1907. Geology and Underground Waters of Luna Co., Neiu Mexico, N. H. Darton, U. S. G. S. Bui. No. 618, 1916. Preliminary Report on Geology and Water Resource of Nebraska West of the One Hundred and Third Meridian, N. H. Darton, U. S. G. S. Professional Paper No. 17, 1903. Artesian Wells of Ioiva, W. H. Norton, Iowa Eng. Soc. 1898. Artesian Well Practice in Western United States, Compiled from Government Report, Eng. News, Vol. 25, p. 172, 1891. Artesian Wells of Colorado, Colo. State Agric. College Bulletin No. 16, 1891. Artesian Wells in Kansas, Robert Hay, 22d Report Kansas Academy of Science. Notes on Artesian Water and the Effects of D'rigation on Sub-Surface Water in the San Joaquin Valley, Eng. Record, Vol. 31, 1894. Artesian Wells in the Red River Valley, Warren Upham, Monograph No. 25, U. S. G. S. The Glacial Lake Agassiz, p. 550. The Geological Structure of the Extra- Australian Artesian Basins, Maitland, Proc. Royal Soc. of Queensland, Vol. XII, April 17, 1896, Relates to the Artesian Basins of the United States. Wells of Northern Indiana, Frank Leverett, U. S. G. S. Water Supply Paper No. 21, 1899. Wells -of Southern Indiana, Frank Leverett, U. S. G. S. Water Supply Paper No. 26, 1899. The Ground Wate7S of a Portion of South Dakota, J. E. Todd, U. S. G. S. Water Supply Paper No. 34, 1900. The Artesian System of Western Queensland, C. J. R. Williams, Proc. Inst. C. E., Vol. 159, 1904-5, p. 315. CHAPTER XVI STREAM PLOW OR RUNOFF 193. Source of Runoff. — The water flowing in streams is derived from two sources, the amount of each being dependent upon the rain- fall and on many other physical conditions on the drainage area : 1. That portion of. the rainfall which passes directly, into the streams as surface flow and which is the principal cause of sudden increase in flow and of floods. 2. That portion of the rainfall which sinks into the ground to reappear as springs and ground flow at more or less distant points, and which in general is the principal source of the ordinary dry weather flow of streams, although in some cases surface storage (i. e. lakes and swamps) becomes a still more important source of dry weather flow. A portion of this seepage may pass into the deep strata and flow away from the drainage area, reappearing in the lower valley or perhaps in distant areas, or even in the sea, but such losses from the seepage water are usually very small. The runoff is that portion of the rainfall that is not absorbed by the deep strata, utilized by vegetation or lost by evaporation and which finds its way into streams as surface flow. The demands of seepage, vegeta- tion and evaporation are usually first supplied and the runoff is therefore the overflow or excess not needed to supply these demands on the rain- fall, or that portion which, on account of topographical conditions, has moved so rapidly that seepage and evaporation have not had time to affect it. The portion of the flow of streams derived from the ground water is that portion of the seepage on the drainage area that has passed down- ward into cracks, fissures or porous beds of the higher parts of the drain- age area, until it has encountered impervious material which has pre- vented its further descent and forced it to some outcrop that has been exposed by the development of the drainage channel into which it dis- charges. 194. Importance of the Study of Runoff. — The study of runoff is important to the engineer in connection with the investigation of public water supplies, water power, irrigation, drainage, storm water sewerage. Study of Runoff. 433 flood protection, navigation, river regulation, etc. In general, the in- terest of the engineer centers around three phases of this question : i st. The total quantity of flow, its annual and seasonal variation and the possible methods of its equalization or concentration. 2d. The maximum quantity of flood flow, its variation during the period of flood, and its reduction or control. 3d. The minimum flow and its possible modification by storage or auxiliary supply. Averages are of little moment. It is not satisfactory to show that the average water supply is sufficient if in one season or year there are flood conditions and in another there is a serious shortage of water or per- haps no water at all available. Water like food must be available when needed, and averages are almost valueless for most engineering pur- poses. A public water supply must command an adequate quantity essentially constant during the year and increasing with the growth of the community. A supply for irrigation must be adequate in quantity and available during each growing season. For successful water power development a continuous adequate supply must be existent or must be made available or else auxiliary power must be provided to take its place. For navigation a sufficient supply must be available during every navigation season. In flood protection, drainage, storm water sewerage, and in the design of spillways, channels or reservoirs to pass or control the high waters of flood periods, the question of the maximum flow and the rate of increase and subsidence of floods are matters of the greatest importance. In some engineering problems the whole range of variation is of im- portance, while in others the maximum or minimum may be the import- ant factor. 195. Occurrence of Runoff. — In general upland areas are wet only during and for a short time following rainstorms until the moisture sinks into the soil or rock, is taken tip by vegetation or is evaporated, or until the surface water drains into the lower lands. The lower lands remain wet for a longer period as they receive not only the direct rainfall but also the surface runoff and perhaps the seep- age from the saturated soils of the higher lands. When drainage is poor the low lands may hold the water for considerable periods and in the case of swamps and marshes may be permanently overflowed ex- cept possibly in very dry seasons, while in other cases, permanent pools, swamps and lakes that are never known to become dry result from im- perfect drainage. Hydrology — 28 434 Stream Flow or Runoff. The channels of streams undergo similar variations. Even in humid regions with small drainage areas and high gradients drainage channels may rapidly pass the waters from a rainstorm and in a few days or even hours become as dry as the surrounding country. In such cases these drainage channels are called dry runs. In streams draining larger areas in humid countries, the varying rainfalls and consequent runoff from widely separated areas, the seepage from porous soils and the drainage Fig. '2r>G. — The Colorado River at Austin, Texas, in Flood. of lakes and swamps furnish a constant supply, variable in magnitude but perhaps seldom or never failing and stream flow becomes perennial. In arid and semi-arid countries the variation in flow is more marked and the drainage channels from greater areas become dry at times. The Colorado River at Austin, Texas, drains an area of about 37,000 square miles and the runoff has been known to vary in quantity from 250,000 cubic feet per second to 9 cubic feet per second. This wide range in flow of the Colorado River is well illustrated by Fig. 256 which shows the river passing over the dam during flood stage, and Fig. 257, which shows the extreme low water flow passing through a narrow channel and through a single gate in the dam. The wide variation in the flow of streams is also shown by Figs. 258 to 261, pages 436 to 439 inclusive. In each case the variation in the flows of the twenty streams used as examples is illustrated by an annual Occurrence of Runoff. 435 hydrograph for a year of high flow and a year of low flow, so that approximately maximum and minimum conditions are indicated. These rivers are so chosen as fairly to represent the great variations in flow in different parts of the United States ; and the location of each stream is shown by the map, Fig. 262, page 440. These hydrographs show that the variations from day to day are. great and that while in general the Fig. 257. — Extreme Low Water Flow of the Colorado River at Austin, Texas.* high water and low water seasons in any stream are essentially similar, they nevertheless are subject to considerable variation. It is quite evi- dent from these hydrographs that the subject of runoff is by no means a simple one and that for practical engineering purposes even approx- imately correct conclusions call for a careful consideration of the many factors on which depend the great variations in flow of different streams and even of the same stream. 196. Difficulties of the Problem. — Practical problems in stream con- servancy involving questions of water supply are greatly complicated by the numerous factors which modify or control this phenomenon and which are so intimatelv related and intermixed in their effects that the *Photo by Mr. Guy Collett, Austin, Texas. 436 Stream Flow or Runoff. Jan. Feb Mar Apr May June My Aug. Sept Ocf Nov Dec Jon Feb Mar ffpr May June July Pug Sept Ocf Mov Dec 4.0 2.0 16.0 14.0 IZO 10.0 SO 6.0 4.0 Z.O IZO 10.0 3.0 6.0 40 20 12.0 1907 \ i \ , . \ ■ ) \i\ 4 1 1 1. i V A K V h m re " V ^ iVWyv 1 UJJJJvv^ Mernmac Piver of Lawrence - Massachusetts Dra/naoe /Jrea 4663 Square Mites 1905 I9IO — 1 ~ 1 \ I \ \ \h J J V \ ll ' \ w uA m L \ |J \f . V J \^.J u t. j J ^ «A V jA / Jv J O \l \J J \ A-vA iV-J / Susquehanna ffivei ol Williarnsport- Pennsylvania Dro/nage Area 5640 "Square M//es /&7 W^V. -^^- J \j V_ 5 Wisconsin Civer af tiilbourn ■ Wisconsin L7ra/naqe Prea 7300 Square Mi/es Fig. 258. — Hydrographs of Various Streams for Years of High and Low Flow. Hydrographs. 437 Jan. teb Mar. Ppr Mag June July Pug Sept Oct. Nov Dec Jan Feb. Mar Ppr May Juneju/u Pug. Sept Oct Nov Dec. 6.0 4.0 Z.O 1909 -A -A -+---|4 4 t--\4a 4 ft ■ --JJJ 4 t-t-t ,X-M m yfi I "KjL ^A^l ^ffiK 1 *=*- 1^ h 1907 . 1 1 v_ JO k *sA 1 . ' Vc WVV k /<2<9 5.0 f0 10.0 . 8.0 6.0 4.0 Z.O o 140- I Z.O 10.0 3.0- 6.0- 4.0 Z.O O- 6 - Savannah Piver at Wood lawn -South Carolina Dra/naqe Prea 6600 Square Mi tes 1 19/Z 4 . 1 1 1 i\ \ A » \ iA vv I "\ /l (\ \ / N V U \ JH v\ A. Ah IV J 191/ 1 \ 7 - /7W /£W/- cv" Jt/banu Georq/a Drainage 4lrea 5000 Square Mites 1909 n \\ \\ 1 1 1 I I J i \ w \ v A. ., — 1904 ^ A % ,,K A 3 Pearl 2iver at Jackson Mississippi - Drainage Prea 31 Z0 Square Miles 1905 \ A f 1 J 1 III JA u < * fV\ NnJ/JJj 4-t . 1 >vj "J ^Jl v y' vj *\ "-X^" 1 1904 1 I A M J l\ J M Vi i I v 1 v~ J s_i J V JvJ v_ . — - .9 - Gasconade 2iver at Pr/inq/on Missouri Droinaqe /5Jtk7 Z7Z5 Square Miles 1900 19/Z \ \ , \ \ 1 j 1 ill 1 ■1 P P\ JL_ , I V. J\ XJ ~^r ~W ^ JU 1 ■»— ,, -JL _=A l 10 Colorado 2iver at Pustin ■ Texas - Dra/naqe Area 34Z00 Square Miles. Fig. 259. — Hydrographs of Various Streams for Years of High and Low Flow. 438 Stream Flow or Runoff. Jan Feb Mar Apr flay June July Pug Sept Oct. Nov. Dec Jan Feb. Man Apr tlau June July flag. 5epf. Oct. Nov. Dec. .Z .6 .4 2 § | io.o l 8.0 \ C 40 X | 2.0 a ° \ £4.0 ! zo.o 18.0 16.0 14,0 12.0 IO.O 8.0 6.0 4.0 2.0 1906 k / . ' I J J ^w ^ rs i i w KJ ^J 19// II Red Piver of the North a/ Fargo North Dakota Oroinage Area 6020 Square Mites Iff/2 IfflO J / v> L \i K. -A. izt 12 Republican giver at Bostwick Ne/rasko Drainage Area 23300 Square Miles 19/3 / r\ \ J . — J" 1910 L yj 13 Yellowstone Piver at Huntley Montana - Drainage firea 12000 Square Mites Iff/3 A id \ V / Wlr ■tz: _j /904 - 14 Spokane Piver at Spokane Washington Drainage firea 4O0S Square Mites. 1899 1 1 — ■ -4 11 I V X% \ 1 H 4 h \l hi n \ V *\ \ T^T^ \ \ \ s t -\ ) ^l\ J l <|(c ) 0)iv ) N.I < )^N(J 5 ) Lr ) 70 60 \50 1 40 ^lhj (J S /0 Coosa R tver above /v7err/mac River above L awrence Mass. Drainage /Irea 7060 Sa. M/. j~/3a/nfa// h Rainfa// * - /' Ri jr 70 /; c \i f\ ?o n OJ c f — - — feS^k^Sj^^fe^^f Fig. 263. — Relation of Total Annual Rainfall to Total Annual Runoff on Cer- tain Streams in the United States. It will be noted that while in general the runoff increases with the in- crease in rainfall there are exceptions to the rule and that evidently no constant relations exist. 444 Stream Flow or Runoff. 199. Geographical Relation of Drainage Area. — The important factors in these relations are (a) size, (b) shape, and (c) location of the drainage area. Each of these factors may have a marked effect on the quantity and regularity of the flow of a stream. (a) Most storms are more or less limited in extent but often include centers of high concentration. A limited storm might cover a relatively small drainage area with marked effect on the runoff, but would have a much different comparative effect on the flow from a large area. A small area which becomes the center of intense precipitation will furnish relatively great flood discharges and consequent great variations in flow. As the size of the drainage area increases, the possibilities of intense precipitation over the entire drainage area are greatly reduced, and with this increase floods in the main streams become correspond- ingly less in relative magnitude. (b) The fan arrangement of tributaries results in high flows reach- ing the main stream at the common center of discharge of the tributaries at about the same time, and causes congestion and consequent extreme flood conditions (Fig. 108, page 197), while a fern leaf arrangement of tributaries (Fig. 264) will in general result in less extreme floods. (c) The geographical location of the drainage area may have a sim- ilar effect. Should the drainage area lie in a direction parallel with the path of intense storms, the precipitation and flow may be greatly in- creased over those which occur where the area extends across these storm paths, and consequently commonly receive intense rainfall only over a portion of the area. The hydrographs of small areas often show the effects of heavy rains by an immediate and marked increase in the flow, as will be npted by a comparison of the hydrographs of Perkiomen Creek and the Kennebec River (Fig. 265, page 446). On drainage areas of small streams where pervious deposits largely obtain, the rainfall is rapidly absorbed and does not radically affect the runoff nor do these streams show greater fluctuations than larger streams : for example, compare hydrographs of the Coosa River and Nottingham Creek (Fig. 265). Large streams do not feel the immediate effect of rainfall on account of the time required for the runoff to reach the main stream. The flow of large streams is also modified by the fact that uniform conditions of rainfall seldom obtain on the entire area. On large drainage areas conditions of rainfall may prevail on one or more of the tributaries only, while on other portions of the drainage area no rain may be falling, with the result that the larger the stream the less be- come the extremes and the greater the uniformity of flow. In some Drainage Area. 445 Fig. 2G4. — Drainage Area of the Wisconsin River. 446 Stream Flow or Runoff. cases streams which are fed by mountain snows at particular seasons as for example, the Sacramento River (see Fig. 261, Hydrograph 20, page 439) or in some locations subject to occasional general heavy rain- ill * t * • a $" ^ '«§ A <§ iC ^ 5 f 3 V V J> ij fl I ^ \aa o 1, ,!\ m 1 ' \ / l\ ' s ) \ \ . 1 f"\ 11 V ^MkP \J _A I A r •Vv *-\ vVyv -i-vA' vw^w rtennebec River Waierwi/e, Me Dra/nage Area 44/0 Square Mi/es ^1 ||QN N 0) oil (8 i y. 8 -52 /904 * » x ' 1 1 1 til 1 i - r \\\ tt- . -t- _ _J . Ml f\ ' E : n Jl ^- -t- - -4- r : \ sly n K 3 _ \ tfa A / | J 1 K vu 0P/4- — Jl. \ri n| s J vJ I^J^JL^ V — 'T- j w° vK>r L. J >^*J ^_J 'V^ - " Rerkiomen Creek , Frec/er/ck , Ra Drainage Area /5a Square S*7//es /SOS /904 ■£^=*- = = 3^^ / 5 30 ^ eo r 1 r \ J^ ^ \ r \K f V, "\r ^ N>-W l W r^*^ 4 § OsouegoPii^er at Batt/e /stand. New York-Dra/naqe Ar~ea ^QSO Square Ft/tes \ SZ.O \ X * ■0 /60 <0 /308 /9c 09 I _ r ktjtt 1 I m, ti J i- X\ irtl - -L A- 4 A I III M t3r . . i 1 L V^ 1 V \ * , wvly ^ \ " V, *au* v*-K*. jv u* M u \J /-#£> <5 ec- 60- 4.0- 20\ (Senesee /2/ver at Ffount MorrtsJVeov YorkrDra/naas Area /070 Square Fti/es. Fig. 269. — Hydrographs of Certain New York Streams. Storage. 459 The effect of surface storage on the flow of streams is well shown by (Fig. 269, page 458), a comparison of the hydrographs of the Hudson, Oswego and Genesee Rivers of New York State. The Hudson River flows from a drainage area (see Fig. 270) having numerous small moraine lakes providing moderate storage. The drainage area of the Oswego River (see Fig. 271, page 460) has an unusual amount of Fig. 270. — Drainage Area of the Hudson River. storage in the numerous lakes of central New York. The Genesee River (see Fig. 2^2, page 461) has only a limited amount of surface storage. A part of the difference in the flow of these streams may be due to underground storage, although this factor is believed in these cases to be subordinate to surface storage. B. Sub-Surface Storage. — Extensive pervious deposits on a drainage area generally produce a high degree of regularity in the flow of a stream. On drainage areas where such pervious deposits are exten- sively developed, the rainfall, especially if the surface be uncovered by vegetation, is rapidly absorbed, becomes a part of the ground water, 460 Stream Flow or Runoff. flows slowly toward the stream and, dependent upon the character of the deposit, reaches the stream only after a lapse of days or perhaps months. As the ground water becomes filled the gradient becomes steeper and the rapidity of its flow is increased. Heavy rainfalls on a \c& t Fig. 271. — Drainage Area of the Oswego River. pervious drainage area therefore will considerably increase the velocity of the ground water flow and hence augment the flow of the streams to a greater extent during or following such periods. As time passes after the occurrence of rains, the gradient will slowly decrease as the water drains from the pervious deposits into the stream, the velocity and quantity of flow become less, and the stream flow gradually de- creases. The decrease, however, is not rapid and a sufficient quantity is often held in storage until further rainfalls augment the stored ground water and a^ain increase the stream flow. With high ground water, Storage. 46 1 such a stream may frequently flow for several months without any ad- ditional rainfall, and the flow is commonly regulated to a greater de- gree by this means than by any other natural condition on the drainage area. The flow from such areas is usually a comparatively large per- centage of the total rainfall. Ground storage in gravels and sand, or other pervious deposits, re- moves to a considerable extent all of the water reaching them from the immediate influence of evaporation and stores them under the very best conditions for the future supply of the stream. Fig. 272. — Drainage Area of the Genesee River. The difference in the effect of surface and underground storage is quite well illustrated by a comparison of the Black and Wisconsin Rivers of Wisconsin, with the Manistee River of Michigan. (See Fig. 273, page 462.) The Wisconsin River drainage above Merrill, Wisconsin has numerous moraine lakes and several artificial reservoirs to store water for power purposes. (See Fig. 200, page 339.) The Black River above Neillsville, Wisconsin, has little storage. The Manistee River has little surface storage, but its drainage area is largely of sand and the regularity of the flow is remarkable. C. Artificial Storage. — Artificial storage created and controlled is usually surface storage and is open to the objections previously men- tioned. It has the advantage of permitting the use of the stored water when and as it is needed, and the entire withdrawal of the supply at other times provided the control is sufficiently extensive. Storage, when introduced on a drainage area, can be used for equalizing flow of 462 Stream Flow or Runoff. 30 28 ^26 fc>24 I k,20 >.I2 V) 8 W/jcons/n /?/rer at Necedah, Wti. / / -' *-J B/ac/r ff/Ver af A/e///j y/ //\j\ r^~_^«-^ M Ma/7/3 tee /P/rer*?/ Jfrer/r/an, M/ct?. V\/\ y A kht Me/yam/H/pe /? near /ronA/oi/nfa/r/jM/c/). J s \s r /Pack f?, fi/£>ra/ /Poctrfoz/jt/t. — >__ fj*j ^7/7. /a»A /^/r ^c/- /)^sy yi//?^ v/ct: /Vox £>e-c. Fig. 273. — Comparative Hydrographs of Certain Wisconsin and Michigan Rivers. Storage. 463 the main stream only with certain points and purposes in view. Fre- quently, where water is stored for various purposes, such as navigation and power purposes, its use for one purpose is found to be antagonistic to other uses. Figure 274, page 464, shows the ideal regulation of the Hudson River based on a proposed extensive reservoir system and on the stream flow for the years of 1908 and 1909. It may readily be appreciated that the regulation secured by such means during a term of years will vary greatly, depending upon the increase or decrease in the annual runoff and on the distribution of the same. An example of the manner in which adequate storage facilities may reduce the flood peak is afforded by the Shoshone Dam near Cody, Wyoming. The normal flow of the river is discharged through two 48-inch circular pipes at the base of the dam, which is 295 feet high from foundation to spillway, and impounds some 256,000 acre feet of water. As the flood waters due to the melting snow come down in June, the reservoir begins to fill and the discharge through the sluices slowly increases with the head, usually in August, the water in the river above the dam begins to grow less than the discharge through the pipes and by November the reservoir is again empty. The effect is to extend the high water flow over the entire summer and wholly to do away with the flood conditions as there has never been sufficient water to cause a discharge over the spillway. 204. Artificial Use and Control of Streams. — When the waters of a stream are diverted or used, all or in part, an effect on the stream flow below the point of use is obvious. Such cases may include irrigation, public water supplies, and supplies for navigation canals. Furthermore the waters may be controlled : a. For water power purposes ; b. For storage to utilize flood flows during low water periods or to mitigate high water conditions in the lower river ; c. For the improvement of navigation by the construction of wing dams and jetties ; d. For pre- venting overflow by constructing dikes and levees which restrict the river to a channel section ; and e. For other public or private conven- iences or profit by various other encroachments upon the waterway often made without intentional interference with the regime of the stream. The construction of dams in a stream for power purposes affects the regularity of flow at every point below the dam, unless offset by a regu- lated discharge. The closing of a power plant, even with water going over the spillway of the dam, will cause a considerable decrease in flow below, as the pond above must fill before sufficient head is gained to 464 Stream Flow or Runoff. 3QOOO Man Apr /Vac/ June Ju/y Ac/g Sept Oct /Vov Dec. Jan Feb. /Van Apr /Vat/ l&k* dfc /9/SGUl. A TtZD FZ. O trVT 4 A /Van Apr- /Vac/Jc/neJo/t/ Ac/a Sept Oct /Vok Dec Jan. Feb /Var A/ar /Vac/ /Varr Anr /Vac/ Jane Ju/e/ Auo. Sept Oct /Vo\r Dec. Jan Feb /Van A/on /Vac/ ^ /o.ooo sQ G kWXI Wafer Was fed Y///A Water tVsea 1 From Stonaae Fig. 274. — Ideal Effect of Storage on the Flow of the Hudson River. After N. Y. State Water Commission, 1910. produce the same discharge. Numerous installations of this kind on a stream often seriously interfere with the regularity of flow below them, and may prove disadvantageous to navigation. (See Fig. 275, page 465.) The diking of channels to prevent overflow of lands often seriously Control of Streams. 465 affects flood heights at and above the lands diked, as the water which was formerly stored by overflow is forced through the restricted channel and more head is therefore necessary. The levees of the Missis- sippi River at and below Memphis, Tennessee, have caused the flood peaks at Memphis to rise more than eight feet above their former level. $30 i Fig. 275. Uan r~e£>. Mar /?pr May xJurte Ju/y Aug. Sept Oct. /Vol/-. Dec. /9/3 P f IV \ n 1 1 \ K hi L \A T0 Jt W V \\ *rw\ rtfVi\ nfVV W v v y nF v T ry yV^ rVyvv tvrr -Hydrograph of Fox River at Rapids Croche Dam, Showing Effect on Flow of Lower River of Sunday Closing of Water Powers. pniii^nM|nMW &s mm y^.. a. Jit* 1 HH It &r j§a|l|L - ! OSi' _ !_ «(» p9MKmH. HH aS'-'^BHli ik^^HM^d MB ^ .-/ MpT ~3^£*- '■ n j^ - ^5^ Fig. 27G. — Obstructions in the Rock River at Janesville, Wis. It is necessary only to point out the radical effect of the diversion of water for irrigation, water supply and the feeding of navigation canals. Such effects are greater or less in accordance with the proportion of water removed from the stream, and the amount returned thereto by the seepage from irrigated lands, from irrigation ditches and the discharge of waste weirs and overflows from canals. Hydrology — 30 466 Stream Flow or Runoff. Wing dams, jetties, and other navigation works are built to improve channel conditions without materially increasing the head at flood stages. The construction of bridge piers and abutments, the filling of low lands and other encroachments on the stream channel, while not intended to interfere with floods, often tend to produce higher flood peaks both by direct contraction of the channel and the opportunities of still greater contraction by the chance afforded for collecting and retaining drift. The obstruction of channels caused by the contruction of buildings over streams in cities where land values are high, some- times results in conditions which may prove serious in extreme floods. (Fig. 276, page 465.) Such obstructions in Mill Creek at Erie, Penn- sylvania, occasioned the great flood losses at that place in August, 1915. 2 205. Conditions Favorable to Maximum Water Supply and Equal- ized Flow of Streams. — Case I. The following conditions are favorable to maximum equalized flow : A. Drainage Area : a. The drainage area must have an impervious bed of such a geological character that no water can sink into its mass and be conducted beyond the drainage boundaries to other areas, but it must be of such nature and capacity that all the precipitation received and not necessarily lost by evap- oration shall pass ultimately to the river channel. b. The surface slope must be slight so that little surface flow will take place even with intense precipitation. c. The larger the drainage area, the less the opportunity for a general intense precipitation which sometimes occurs on small areas, and the less the variation in flow under varying conditions of precipitation throughout the year. d. The temperature on the drainage area must be moderate, cool to reduce evaporating effects, and above freezing so that the surface may never become impervious through the forma- tion of ice, or receive precipitation as snow, with resulting loss from evaporation. B. Precipitation : a. The larger and more uniform the distribution of the annual precipitation, the greater the stream flow and the more per- fect its equalization. - Eng. News, August 12, 1915; also Eng. Record, August 14, 1915. Equalized Flow. 467 b. The precipitation should be moderate in intensity so that it may be absorbed by a pervious surface and without sur- face flow, but never so light as to result simply in the mois- tening of the surface, with consequent loss by evapora- tion of the small precipitation thus received. c. For maximum water supply, maximum precipitation or high precipitation, with other favorable conditions, is essential. Whatever the precipitation may be, the maximum amount of runoff will result when the maximum proportion of the precipitation is preserved to the stream. For equalized stream flow, a uniform distribution of precipitation through each and every year is most favorable, and any variation in precipitation must be offset by inter-precipitation storage which, however, must not result in undue evaporation. C. Storage : a. In order that evaporation may be a minimum and hence the water supply a maximum, there must be no surface storage, and the river channel must be comparatively deep and nar- row, with a minimum exposed water surface. b. To provide storage and equalize the otherwise irregular stream flow due to the natural irregularity in the occurrence of precipitation, the impervious bed of the drainage area must be covered deeply with pervious sandstones or sands, not so coarse as to permit rapid flow through their struct- ure but coarse enough to receive the rainfall rapidly into their mass in order to avoid evaporating influences at the surface and to convey the waters deep enough so that cap- illary attraction will not draw them to the surface and sub- ject them to evaporation. The surface must be free from vegetation and be unobstructed by roots which would pro- duce similar effects. For conditions favorable to maximum runoff and equalized flow es- sentially as described above, consider a broad deep impervious rock- valley deeply filled with sand and gravel, the surface devoid of vegeta- tion and with the stream meandering through the center of the pervious plain. The rain falling on this area will sink rapidly into the pervious deposits and move slowly toward the river. Little of the water will be lost in evaporation because the rainfall will immediately sink below the surface and reach the ground water where it is not subject to evapora- 468 Stream Flow or Runoff. tion effects. The great deposit of sand and gravel will store the water, retard its flow and permit it to move slowly towards the stream which will be fed with great uniformity, and while the ratio of rainfall to run- off in such a stram will be high, it will at the same time be distributed with considerable uniformity throughout the year and the stream will be perennial. These conditions will result in equalized flow, the degree of uniformity depending upon the perfection of development of the domi- nating factors mentioned above. There are few examples of extremely favorable conditions of this character. However, an illustration of the results of the occurrence of such factors to a high degree is shown by the hydrographs of the Manistee River of Michigan which flows through a sandy country where underground storage is highly developed. (See Fig- 273, page 462.) 206. Conditions Favorable to Maximum Variation in Water Sup- ply of Streams. — Case II. For the maximum variation in the water supply of streams, the extreme case occurs when torrential flows, fol- lowing heavy precipitation, are succeeded by dry stream beds shortly after precipitation has ceased. The following conditions are favorable to maximum irregularities in flow : A. Drainage Area : a. In this case the conditions of maximum quantity and inten- sity of runoff require an impervious rocky drainage area. b. The drainage area must have a steep channel and abrupt slopes to the divide. The rock surface must be smooth, and both main and lateral channels unobstructed. c. No soil or mantle deposits, no vegetation, no storage, surface or subsurface, must exist to obstruct or delay surface flow if the maximum torrential stream flow is to result. d. The temperature must be mild to avoid storage in the form of ice or snow, but not too warm or evaporation will reduce runoff. e. The smaller the area, the more surely will areas of intense rainfall cover the entire drainage area and produce extreme conditions. R. Precipitation : a. The precipitation must be concentrated in a limited rainy sea- son with continuous downpours, followed by long continued droughts. Light rain would increase evaporation and de- crease the total discharge. Maximum Variation in Flow. 469 A modification of the above conditions, leading in some cases to equal or more extreme conditions, might be occasioned by great deposits of snow during winter months followed by rapidly rising temperatures on the advent of spring when the combination of torrential rains and melt- ing snow might result in maximum runoff. Under the above conditions the heavy precipitation of intense storms accompanied perhaps by the waters from melting snows will flow rapidly and unimpeded down the smooth and abrupt slopes to the channel and rush down its steep gradient to its outlet, leaving a dry stream bed soon after the rain has ceased. The predominating influence of factors tending to irregularity of flow are shown by the hydrograph of the Gen- esee River, Figure 269, page 458. This example is not an extreme case, for this stream is seldom or never entirely dry ; its hydrograph shows the resulting conditions somewhat better than in the case of streams which entirely cease to flow at certain times in the year. 207. Conditions Favorable to Minimum Runoff. — Case III. The following conditions are favorable to minimum runoff : A. Drainage Area : a. A pervious soil over a pervious rock bed from which the seep- age waters will be permanently lost to the stream. b. A low, flat drainage area largely covered by shallow swamps, filled with vegetation, from which the flow will be sluggish and the evaporation large. c. High temperature and strong winds, to increase evaporation, reduce humidity, and rapidly remove the humid atmos- phere. B. Precipitation : a. A small rainfall occurring in light showers, well distributed throughout the year. An excessive development of these conditions may result in no flow from a given area. Such conditions are not rare but as a rule are confined to very small drainage areas. There are numerous examples of such conditions found in Wisconsin and these examples are of two classes : 1. Small sinks in sandy soil from which the rainfall partially evap- orates and partially sinks into the soil and flows to the main drainage channel of the general drainage area on which the sink is a local develop- ment. Similar sinks are also found in many limestone regions. In both cases seepage may be a considerable factor in rainfall disposal. 470 Stream Flow or Runoff. 2. Small depressions containing lakes which occupy a large propor- tion of the drainage area. In such cases seepage is a minimum and evaporation a maximum cause of rainfall disposal. 208. Discussion of Extreme Conditions. — In Sec. 207, Case III, are illustrated the limiting conditions of no supply and this case needs no further discussion. Cases I and II embrace the extreme conditions of maximum water supply and uniformity of stream flow on the one hand (Sec. 205) and of maximum irregularity on the other hand (Sec. 206). In either case increased drainage area tends to greater regularity of flow but almost any other change or modification of whatever nature will disturb the condition and produce opposite effects in the two cases considered. The introduction of surface storage on these areas will in- crease evaporation in both cases, and hence will decrease total discharge ; but it will decrease regularity in Case I, while it will increase it in Case II. In Case I the occurrence of forests or vegetation of any kind on the drainage area will obstruct the pervious surface deposits and reduce the free access of water. The lighter rains will be kept entirely from the soil and evaporated from the surfaces of leaves. The forest bed will hold the moisture from the soil and conserve it for plant use. The roots will draw the moisture of the pervious soil from considerable depths. In each case a reduction in flow and a tendency to irregularities will result. In Case II the occurrence of forests on the impervious area, the forest bed, the vegetable fibre, the cracks opened by the roots, all offer both obstruction and limited storage and, while slightly reduc- ing the discharge, tend to equalize flow. LITERATURE RELATION OF RAINFALL AND STREAM FLOW Flow of the West Branch of the Croton River, J. J. R. Croes, Trans. Am. Soc. C. E., Vol. 3, p. 76, 1874; Vol. 4, p. 307, 1875. The Flow of the Sudbury River, Mass., A. Fteley, Trans. Am. Soc. C. E., Vol. 10, p. 225, 1881. Rainfall Received and Collected on the Watersheds of Sudbury River and Cochituate and Mystic Lakes, Dexter Brackett, Jour. Asso. Eng. Soc, Vol. 5, p. 395, 1886. Rainfall, the Amount Available for Water Supply, Desmond Fitzgerald, Jour. New Eng. W. Wks. Assn., 1891. Rainfall, Flow of Streams and Storage, Desmond Fitzgerald, Trans. Am. Soc. C. E., Vol. 27, p. 253, 1892. Rainfall and River Flow, C. C. Babb, Trans. Am. Soc. C. E., Vol. 28, p. 323, 1893. Relation of Rainfall to Water Supply, Charles E. Greene, Mich. Technic, Mich. Univ., 1895. Literature. 47 1 Data Pertaining to Rainfall and Stream Floio, C. T. Johnston, Jour. Wes. Soc. Eng., Vol. 1, p. 297, June, 1896. Runoff of the Sudbury River Drainage Area, 1S75-1899, Inclusive, C. W. Sher- man, Eng. News, 1901. Relation of Rainfall to Runoff in California, J. B. Lippincott and S. G. Bennett, Eng. News, Vol. 47, p. 467, 1902. The Relation of Rainfall to Runoff, George W. Rafter, U. S. G. S. Water Sup- ply, Paper No. 80, 1903. Rainfall and Runoff on New England Atlantic Coast and Southwestern Colo- rado Streams, W. O. Webber, Jour. Asso. Eng. Soc, Vol. 31, p. 131, 1903. Rainfall and Runoff from Catchment Areas in New England, L. M. Hastings, Jour. New Eng. W. Wks. Assn., Vol 18, p. 32, 1904. Twenty Years' Runoff at Holyoke, Massachusetts, of the Connecticut River, Clemens Herschel, Trans. Am. Soc. C. E., Vol. 58, p. 29, 1906. Comparison of Rainfall and Runoff in the Northeastern United States, John C. Hoyt, Trans. Am. Soc. C. E., Vol. 33, p. 452, 1906. Length of Records Necessary for Determining Stream Flow, John C. Hoyt, Eng. News, Vol. 59, p. 459, 1908. Rain and Runoff near San Francisco, Cat., C. E. Grunsky, Trans. Am. Soc. C. E., Vol. 61, p. 496, 1908. The Yield of a Kentucky Watershed, G. L. Thon and L. R. Howson, Jour. Wes. Soc. Eng., Vol. 18, p. 634, 1913. FORESTS AND STREAM FLOW A. Favorable to Forest Influences on Runoff Decrease of Water in Springs, Creeks and Rivers, Contemporaneously with an Increase in Height of Floods in Cultivated Countries, Gustav Wix, Nos. 6 and 9 Papers of Society of Austrian Engineers and Architects, 1879, Translated by M'aj. G. Wetzel, U. S. A., Washington Govt. Pt. Officers, 1880. The Influence of Forests upon the Rainfall and upon the Flow of Streams, Geo. F. Swain, Jour. New Eng. W. Wks. Ass'n, Vol. 1, March, 1887. Data of Stream Flow in Relation to Forests, Geo. W. Rafter, Ass'n C. E., Cor- nell Univ., Vol. 7, p. 22, 1899. Forest Influences, U. S. Dept. of Agric, Forestry Div., Bulletin No. 7, 1902. Forests and Water Supply, C. C. Vermuele, Ann. Report State Geol., New Jersey, 1899, p. 137. New Jersey Forests and Their Relation to Water Supply, C. C. Vermuele, Ab- stract of Paper before Meeting of the American Forestry Ass'n, New Jer- sey, June 25, 1900; Eng. News, July 26, 1900; Eng. Record, Vol. 42, p. 8, July 7, 1900. Forests, G. W. Rafter, Hydrology of the State of New York, Bui. 85, N. Y. State Museum, 1905. Saving the Forests and Streams of the U. S., Dr. Thos. E. Will, Jour. Frank- lin Inst. May, 1908. Conservation of Water Resources, Floods, M. O. Leighton, U. S. G. S. Water Supply Paper 234, 1909; also Rept Natl. Conservation Comm. Senate Doc. 676, 60th Cong. 2d Sess., Vol. 2, 1909. 472 Geology. Surface Conditions and Stream Flow, Wm. L. Hall and H. Maxwell, U. S. Dept. of Agri., Forest Service Circular 176, Jan. 11, 1910. Influence of Forests on Climate and on Floods. G. F. Swain, Am. Forestry, Vol. 16, p. 224, 1910; also Eng. News, Vol. 63, p. 427, 1910. B. Adverse to Material Influences of Forests on Runoff Forests and Floods, Roberts, Am. Eng., April 11-25, May 2-30, June 6, 1884. Forests and Reservoirs in Their Relation to Stream Flow, Etc., H. M. Chitten- den, Trans. Am. Soc. C. E., Vol. 62, p. 245, 1909. Forests and Floods, Extracts from an Austrian Report on Floods of the Dan- ube with Applications to American Conditions, Lieut.-Col. H. M. Chitten- den, Eng. News, Vol. 60, p. 467, 1908. The Relation of Forests to Stream Flow, Editorial Eng. News, Vol. 60, p. 478, 1908. Deforestation, Drainage and Tillage, with Special Reference to Their Effect on Michigan Streams, Robert E. Horton, Jour. Michigan Eng. Soc, 1908. The Relation of Forests to Stream Floxo, Maj. Wm. W. Harts, Extracted from Memoirs Corp. of Eng. U. S. A., Oct.-Dec, 1909, Eng. News, Vol. 63, p. 245, 1910. A Report on the Influence of Forests on Climate and on Floods, Willis L. Moore, House of Rept., U. S. Committee on Agriculture, 1910; see also Eng. News, Vol. 63, p. 245, 1910. Report on Relation of Forests. to the Floio of the Merrimac River, Mass., Lieut.- Col. Edward Barr, Doc. No. 9, House of Rep. 62d Cong. 1st Sess., 1911; see also Eng. News, Vol. 66, p. 100, 1911. The Flow of Streams and the Factors that Modify it, with Special Reference to Wisconsin Conditions, D. W. Mead, Bui. No. 425, Univ. of Wisconsin, 1911. Influence of Forests on Streams, L. C. Glenn, Eng. Assoc, of South, Vol. 21, p. 67, 1910. CHAPTER XVII VARIATIONS IN RUNOFF OR STREAM DISCHARGE 209. Importance of a Knowledge of the Variation in Stream Flow. — The hydrographs previously discussed indicate ,in general great di- versities in the discharge : 1. Of different streams. 2. Of the same streams during different years. 3. Of the same streams during different seasons of the same year. These differences have marked influences on the availability of each stream for utilitarian purposes depending upon these variations and the uses to which the stream may be applied. In order to make the use of a stream practicable for the purposes of a public water supply, navigation, water power or irrigation, it must be possible to secure a sufficient supply of water as needed and at a cost low enough to make the project financially feasible, otherwise the project should be abandoned. In every project the needs or demands for water and the supply are both more or less variable and are af- fected by the seasons, the climate, and by many other conditions. When only small supplies are to be taken from large lakes or rivers, the va- riations in runoff may be of little relative importance ; but when, as in many cases, the source of supply is to be developed to the maximum practicable extent, the problem of conserving and utilizing the irregular flow of a stream so that it may be made available at the time and in the quantity needed for a given purpose, is important. Every problem of this kind is essentially different from every other similar problem and must be considered by itself and in the light of all modifying influences. In considering such uses therefore any examples are only illustrative of special conditions and in every case the engineer must investigate for himself the nature of the demands of his project and the possible supply available from the particular source from which such demands must be met. 210. Consideration of Public Water Supplies. — In the considera- tion of water supplies for most projects, not only the present but the future demands, must receive attention. The water needed for a public supply will increase with the growth of population ; it will vary from day to day with the season, with the humidity and with the tem- perature ; it will be less at night than in day time. In every problem 474 Variations in Runoff. these factors and often many others must be considered in connection with the source of supply and in the plans for its development. Fig. 277 shows the variation in both annual and monthly pumpage at Milwaukee, Wisconsin, together with the growth in population sup- plied. As Milwaukee draws its supply from Lake Michigan and that source for the purpose is unlimited, these variations are of importance only in the design of the system ; but if on account of gross pollution of the lake, Milwaukee was obliged to turn for a supply to upland streams, the future increased demands and their variations together with the variations in the flow of the stream considered would be of 70 65 60 h55 <5 Q ^ 50 lb C -35 ^ 30 35 20 fl fl J, A. f A\se Dai Tfnf /y C >'re ynsumpf/o Year- — . n 1 h n 1 -V i ' I I VI v f J \ i \ f X >■ r J \ y 1 jAr nJ p i e^ f '&\ tit 0^ oV£^ -1 60O 5 75 550 \ 585 c 50O \ 475 K 450 c: 435 < 400 \ I 375 350 /905 /906 /907 /908 7909 79 7 O 797/ 79/3 79/3 79/4/9/5 79/6/9/7 Fig. 277. — Variations in Monthly and Annual Pumpage at Milwaukee, Wis. great importance in considering the adequacy of such sources and the works needed to make the source useful to its maximum limits. 211. Consideration of Supplies for Power Purposes. — For water power purposes studies of available supply and probable demand are not less important than for other projects. Fig. 278 shows the flow of the Peshtigo River, the power output of the plant (see Frontis- piece), the water stored and drawn from storage, the fluctuations in the reservoir surface and head, and the water wasted. To determine the practicability of utilizing the irregular flow of a stream for water power purposes, a study of its hydrographs, of the available heads, of the probable demand for power, of the available pondage or storage and of their economic relations is necessary. Supplies for Power. 475 433-/ Ul UO/J.0A3/J ~/3JO/\/ P&3H "^ ^ ^ pU003£- ^aaf -f.33_J U o/qnQ u? aS-JOc/qs/Q 476 Variations in Runoff. 212. Consideration of Supplies for Irrigation. — For irrigation pur- poses comparisons of supply and use are also essential. In many cases irrigation supplies are needed for only certain months in the year 5ALT f?/VER . 727 _^=l__^ 1 __Ii= _____:- :____f___-__=jL__ r A NJ f : ^f ^4JJJJjiJftk| [Lji 1 111 M Mfijii^ :tt?"%$r n? X/////^//^/ 5T = _jt ^T__ Q^ _ - . _ ^ - | -* 0/ i"" -±--- "::;::::::::=i:: t ~ in Q/ - -_ + . - _ I I- = :I L_. /9/e /9/3 /9/4 Z9/5 /9/6 /9/r BO/5E "" ~ " j__ - - - J - J x " p44^^J4 ^^zz^/^ __■ _.- ___ _-]_ -•r ~ 3 ;>^7 S ! -. :: -;;, ^_ _ 4 T - - _ _ I :. .____: : :_. _ -_L „ /9/? /9/J /9/4 /9/5 . /S'/dS' /9/r BELLE EOURCHE " t "" -- -'"T " T //z/_l " I " ■• i ' _L r>* • z< : _u r — — us /^ i^^__._ .J////*-.. J____ .__h ^ji/sL ///// /"// n i . ^P da 7/ <4 iz/z^ . . „ /+■.... Z2ZZZ o : ^_ _ft>)^ Q,3 ____- <_^ _ :::::£ -±A , \ 7777773 _1_ ////// 7//AA/ n -, ////// ///AA/ 02 I V///A V///IL __: a, =. - " '/AM t*"<*A L Ul 1 1 "'^Z* _l ■ - --_ -!---_=_ __=__ _ /:£< — ^ ■g\6 w p& ■gT3 +0 ' /, *- s / >/ o 3 6 3 /e /5 /a e/ 24 27 30 Discharge - Thousands- of Cu6/c feet per Sec O. Unsatisfactory /7af/ng Carre /6 \ 3 0/23-456 789/0 / 23456 7 8 9 /O Discharge-Thousands of Cubic Feet per Sec. Discharge-Thousands of Cubic feet per Sec. £T. Change in fiafing Curve due to Changed Section. f\Chanqe in Rat/ng Carve due to Tee in Section. Fig. 282. — Types of Rating Curves. Hydrology — 31 482 Variations in Runoff. of the section and while the gage height (Bh) may remain the same for these conditions, the actual discharge through the section will be greater or less than with constant flow. 216. Difficulties in Stream Measurements. — Unfortunately for the purpose of stream measurements stream channels vary radically from place to place in section, slope and character of bed, and the flow is not uniform but is constantly changing in quantity and consequently in slope. In practice, the flow of -streams at various times and with various heights of water only approximates that indicated by a rating curve because : 1. The gaging stations may be improperly selected with regard to controlling sections, bends in the channel, obstructions to flow, etc., and thus be incapable of development as a suitable gaging station. (Fig. 282 D.) 2. Measurements may be made with a rising or falling stream when the gradient is greater or less than that corresponding to a uni- form flow for the corresponding elevation of the stream. (See Fig. 281.) 3. The measurements from which the curve is established may be in error for accuracy can be attained only by experience and care. 4. Cross sections unless in rock frequently change by scouring or may in any section be changed by the deposition of debris (Fig. 185, p. 327), thus altering the relation of gage height to discharge. (Sec Fig. 282 E.) 5. The elevation of the water surface of streams may be greatly affected near the outlets by backwater from the rivers into which these streams flow and may at almost any point be affected by backwater resulting from jams of ice or logs, by the lodgment of materials or by the growth of aquatic grass and weeds which increase gage height while they reduce the corresponding stream flow. 6. Even when the section chosen is fixed and satisfactory and the rating curve well established, only continuous gagings by a continuous recording gage will account for all the fluctuations in flow due to normal changes and artificial control of stream flow, and gagings taken only once per day may not fairly represent the flow of the stream for that day. (Fig. 55, p. 102.) 7. Friction of flow is greater with an ice covered river, and a rating curve for ice conditions will differ greatly from the curve for an open channel. (Fig. 282 F.) In northern streams when ice is forming in a channel there is always a period of indefinite flow, for during the Measurement of Stream Flow. 483 formation of ice the flows must necessarily change from those indicated by the rating curve for open conditions to those indicated by the rating curve for ice conditions, and the same change will take place on the breaking up of the ice in the spring. Such changes cover only a brief period, however, and are less important than other factors mentioned. Gagings made at dams are frequently in error on account of : i. Errors in discharge formula or discharge curve used. 2. Leakage around or under the dam. 3. Lack of continuous gagings with rapidly varying streams. For the above reasons many of the published gagings of streams are somewhat in error and consequently misleading. In many of the later stream gagings published by the Hydrographic Branch of the United States Geological Survey the relative reliability of the gagings is indicated. In all cases the gagings should be investigated before they are used as a basis for important conclusions. 217. Runoff Data and Their Use. — The Hydrographic Branch of the U. S. Geological Survey has for many years been making observa- tions of runoff on various streams in the United States. 3 The number of gaging stations has gradually been increased as funds have become available, and in many cases the work has been considerablv exiended by State and private aid. In the earlier days of this work on account of inexperience and the lack of sufficient funds, many records were of more or less doubtful character, but some have been reviewed and rendered more accurate by later studies and investigations and have been republished in a corrected form. In spite of the increasing ex- tent of this work, it is frequently found when a new development is considered, that there are no data bearing directly on the project. Observations have often been made on neighboring streams or at other stations on the same stream, and conclusions must be drawn from the data available. Under these conditions it becomes imperative that runoff relations be investigated in order that such relations may be utilized to modify or confirm the available data for the use of the pro- ject under consideration. Unfortunately these relations are neces- sarily more or less discordant and inexact but this fact is common to all engineering data and should not stand in the way of an attempt to secure the best possible knowledge of the principles from which correct and conservative conclusions may be drawn. Where meteorological records and stream flow measurements are available the pertinent data most readily obtainable for an area arc in See Water Supply Papers of U. S. Geological Survey. 484 Variations in Runoff. the order of their importance: runoff (local and comparative), mete- orological conditions (precipitation, temperature, wind velocity and humidity), physical conditions (topography, geology, surface and sub-surface storage) and surface culture (forests, vegetation, cultiva- tion, etc.). Data concerning stream flow can be obtained from various publica- tions and from the local Hydrographic office of the U. S. Geological Survey. Meteorological information can be obtained at the local Weather Bureau and from the publications of the U. S Weather Bureau. Some information concerning physical conditions on a drain- age area are often available in various State and United States Geolog- ical publications, but detailed data covering topography, geology and the physical condition of the drainage area as regards storage; soil, vegetation, etc., can be obtained only by observation and even then can be only generally known. The runoff data needed by the engineer in the solution of his various problems may vary greatly. A knowledge of the average annual streamflow is seldom sufficient even with large storage although the equalization of dry periods of several years by storage is sometimes possible. Even in such cases a knowledge of the distribution through the year is desirable at least to the extent of monthly flow. With small storage or with no storage available the flow of a stream from day to day becomes of great importance. In other problems the extreme conditions of drought or flood or the probable height of water levels are the controlling data and here local records are seldom sufficient, for considering the short time of observa- tion it is seldom safe to conclude that such extremes have been reached, and the engineer must gather information from many other besides local sources as a basis for conservative conclusions. For comparative purposes the flow from streams of known drainage areas must be available. It is not sufficient that the quantity of dis- charge of a certain stream be known, for such fact is of no value for comparative purposes unless the number of square miles of drainage area is also known. When comparative hydrographs of the monthly flows of a stream in cubic feet per second per square mile are to be used as a basis for stream flow computations, another doubtful element is introduced by estimating the drainage areas of the two streams that are to be compared. Engineers are cautioned against this source of error in various publications of the Hydrographic Branch of the U. S. Geological Survey. 4 4 U. S. Geol. Survey, Water Supply Paper 353, p. 15. Runoff Data. 485 "Even though the monthly means for any station may represent with a high degree of accuracy the quantity of water flowing past the gage, the figures showing discharge per square mile and depth of run- off in inches may be subject to gross errors, which result from including in the measured drainage area large noncontributing districts or omit- ting estimates of water diverted for irrigation or other use. 'Second feet per square mile' and 'runoff (depth in inches)' have therefore not been computed for streams draining areas in which the annual rainfall is less than 20 inches, nor for streams in which the precipitation exceeds 20 inches if such computations might probably be uncertain and mis- leading because of the presence of large noncontributing districts in the measured drainage area, of omitting estimates of water diverted for irrigation or other use, or of artificial control or unusual natural con- trol of the flow of the river above the gaging station. All values of 'second-feet per square mile' and 'runoff (depth in inches)' previously published by the United States Geological Survey should be used with extreme caution and such values in this report should be used with care because of possible inherent sources of error not known." In few cases are available maps sufficiently accurate to permit, with any great degree of accuracy, the determination of the drainage area of large streams. It is therefore evident that not only is measured stream flow s'ubject to more or less error but the drainage area from which it flows is known only approximately and when such data are used for comparative purposes, the exact drainage to which it is ap- plied is also somewhat uncertain. 218. Variation in the Discharge of Different Streams. — It is evi- dent that if all things were equal the runoff or discharge per square mile of drainage area for all streams would be the same. In reality great differences occur in different. parts of the country in the various factors that affect runoff (Sec. 197) and in consequence there are cor- responding great differences in the flow of different streams. Some of these differences are shown by the hydrographs of Figs. 258 to 261, pages 436 to 439 inclusive, where rivers widely separated (Fig. 262) are each represented by a year of high flow and a year of low flow. It should be noted that these hydrographs show the discharge in cubic feet per second (hereinafter abbreviated as second feet or sec. ft.) per square mile of drainage area so that they are strictly comparative except that some of the hydrographs (Nos. 11, 12 and 13) are drawn to a scale ten times greater than the others. The high waters shown by these hydrographs vary from as high as 24 cu. ft. per sec. per square mile to as low as .38 sec. feet per square mile, and the low water flows 486 Variations in Runoff. vary from as high as one sec. ft. per square mile to as low as .01 sec. ft. per square mile in the years of high flow. In areas widely separated such variations would normally be expected, and it is evident that there is little advantage in a comparative study of the flow of streams not contiguous and physically similiar as a basis for estimating the varia- tions in discharge which may be expected. In streams that are closely adjoining the comparative discharge may be expected to more nearly agree, but even under such conditions it is evident by a comparison of hydrographs that the physical conditions of the drainage area of various streams in the same state may be so greatly different as to result in large differences in their annual and seasonal discharges. This wide difference is shown by Fig. 269, page 458, which shows the comparative discharge of the Hudson, Oswego and Genesse Rivers in New York State. In the cases just stated the drain- age areas are not contiguous, but even when they are nearly so as in the case of the Black, the Wisconsin and the Rock Rivers of Wiscon- sin (Fig. 273), the conditions are frequently so different that both the high and the low stream flows differ radically in quantity, and the stream flows are not safely comparative. On the other hand it is true that when streams are adjacent and conditions are reasonably similar, a fairly close comparison exists in both the quantity and distribution of their annual flow (Fig. 283), and this agreement is frequently quite as close as is found in the comparison of flow at different stations on the same stream (Fig. 266, p. 449). and often within the limits of the factors of safety which should be applied to runoff estimates. 2ig. Variation in the Discharge of the Same Stream. — The hy- drographs of Figs, 258 to 261 inclusive, show not only the variation in the flow of different streams but also in each case a hydrograph for a year of high flow and for a year of low flow is shown. From these hydrographs therefore an idea can be gained not only of the great difference in flow between different streams widely separated geograph- ically, but also of the great variations that occur in the runoff of in- dividual streams during different years. In long terms of years even greater variations in runoff sometimes occur than are there indicated. To obtain a full knowledge of the variations in the flow of a stream it is essential to study its hydrographs for a long term of years. The extreme maximum and minimum conditions of stream flow are even more rare in their occurrence than those of maximum and mini- mum conditons of annual rainfall, and it will be recalled by reference to Fig. 122, page 220, that the extremes' of annual rainfall at Boston that occurred in the fifty years prior to 1868 have not recurred in the Variations of a Stream. 487 Jan Feb. Mar Apr May June Ju/y Aug. Sept Oct A/ov Dec 20 O.O %25 /Venom/nee £?/\/er Near tron /^oun tain. Mich Dra/nage Area 24/3 Sq.Mi 005 kO.O ^25 Peshtigo f?i\/er at Hermans farm Drainage Area &7Q 3a. Mi. O.O Chippewa River at Eau C/aire Drainage Area 6740 3q.Mt Fig. 283. — Hydrographs of Four Rivers in Wisconsin for 1908. 488 Variations in Runoff. Q ! jjj \ 1 III 1 N /I 1 • 4-\ ^ "^_ i/j f 5 " :-=s / ^ f= ~^-L ! ^ iT 5 i J^ 5-j-f^i- ^f 81 <£ i y i> V \ r>7 ^s 'y „■ ^. N, \i >i' K 1 i^j < ! -tf 05 0) p ^ 5|V: 5[ ,*T j ' "S; l/l | 5 -^-' 5 > l/T ! ?; W , J^i ■ ~~v^/_ j "7 -, ^> J ^3 x =4-*-j '"~i-vU,i =cd^J «£^ vTJ> ^^Jr ^ ! I&i 1 Kj ■ i\ r^^? \-J k ; !fj ! 1 : 1 < i i l/i ^ / /' / "i i r 1 j "fc| a i (j !> ! li ' ' -rtfc hj- h^i ^\ \lJ- Ttt ^- s ' S i -^f ■«* ■?■■ 1 hH ! ^ "' ^L; -~* !\ ! t?, ! \ H f\ii 1^ ' «£ 1 ~r"?i 'f ^ £1 0) iy Z 7 8 : ]/ «d* ! § i< * * *Tj <6 >+' 1 o i ^S ' O) &■ l5 1/ i -r-r '*"<>' V \ '^ F ■ \ T~ % gT c -- I ^ "^ \ 7^ ] C; | ': V i 1 v J £■ i^ K3 /] X "V i ' J 3 j ^r c izX u = -^t ; "' i' ■=2 2- = =g ! < K" . ^c ^c -5f 6' t^\ % it jslg: § ^ -2 "E § 5| I " *> < : "O "-i r t^6 85 ^2 S :^ 5 j< 5i , OJ ■«=-■* / * «»? S i / y "^ ,' ' ■* Z% s=» A ■< ■ ^ -^1 y i '^-^ 't T ' ^>v ~ =l ~ " V* Ld -*- I <= S> ^A " A ^C - •^ ?! i J 4^ ^ JC « _Su -t-t 2^ j jt : r^ f P^ ^ r> T' 1 < ^ / (» pi 'r ^ r v '£ l ,S T ^s ■ )i s'"' i ;] 01 gj "Z.' X J~ S -r=i r S ,t " 3 01 5 <> v •% * - /] —k- 4 ^ k= — d — =3p /? *S "* * _^* 1 *7 5t tJ _^* L? ^~H ,c ^ J ^i- ( > '? ^^ \ ^ ■\\ \ ! \ 1 A. dt XJ j 1 "T* ^ H? fr ■ n* * III' 3F \. 1 3 t ~^, ^i ^ ^i 2 \_r^ \ M ""* ^ -^i_ ', oo / / 0' d I nfe 0' y / / <•' A / -. / ,-> / / / 1 J ~-^3SS ; -^' I 1 6* * -9- y s ^ J /905, s '" ,. w p. „ ■» -v '<;<"■ / 1 | / 1 / ' / A ^ ; p V r s n? \ a (, • 9- / / /7 y' / ^.— - -•' JL S^-xS-" " \ ^ y J 5 .? 19%, 10%, 4% and 2% of the total resulting runoff. Any meas- urements of such effects cannot be more than approximate and apply only to the individual drainage areas for which they have been deter- mined. The method of study used by Mr. Stewart was as follows : "Referring to the year 1907 (see Fig. 288) , the ordinates to the curved lines, starting with the given average monthly runoff and drawn down- ward and to the right, represent approximately the rates of runoff, if no rain should occur subsequent to the month for which the respective curves, representing the underground flow was determined as follows : In September, 1907, the average monthly rainfall was 6.08", 1.88" above the fourteen year average. The heavy rains were distributed over a period of about a week near the middle of the month, the heavier rains at single stations being about 4.6 inches. "The rainfall in each of the months, October, November and Decem- ber, was very small, amounting to 0.87", 0.69" and 0.42" respectively. The maximum daily rainfall at any one station in October and Novem- ber was about 0.40", with rains at other stations on or about the same dates averaging about 0.20". The maximum rainfall in December at any one station was 0.30", with rains at other stations averaging about 5 Storage Reservoirs, by Clinton B. Stewart, Wisconsin State Board ' of Forestry, 1911. Effects of Storage. 495 o. 10". The amounts and distribution of the rainfall in these months was such that very little runoff could have resulted therefrom. Esti- mating the probable values for the runoff from these small rains, the Variation offlcfua/ Rain fa// from /4 Year Aire rage f/pove Merril/ +0.53 -045 -003 +O.06 -f.47 -/.I7 ~ /Z5 -O.74 +1.83 -2.07 -J.20 -0.59 FPainfa/l Deficiency from Jan I, from 14 Year Average +0.53 +0.08 +OOO +0.06 -1.41 -Z.S8 -3.83 -4.57 -2.69 -476 -5.96 -6.55 Jan. feb Mar flpr May June Ju/y f/ua Sept Ocf Nov Dec Fig. 288. — Ground Flow on the Upper Wisconsin River. After C. B. Stewart. curve A H may be drawn. Ordinates to this curve at points A, C, E, etc., would represent with reasonable accuracy, the runoff for the cor- responding months of September, October, November, etc., if no rains had occurred subsequent to September. The ordinates to the curve I H 1 , similar in form to A H, at I, B, D, F, etc., would represent the runoff for the corresponding months of August, September, October, November, etc., if no rains had occurred subsequent to August." Similar studies to those of Mr. Stewart are the basis of the ground 496 Variations in Runoff. flow diagrams of Mr. C. C. Vermuele (Fig. 289), which he used to calculate the dry weather flow of streams from estimated depletions of the ground water. Vermuele found that the flow with full ground water in Eastern streams was in general two inches per month, and that when the depletion of the ground water occurs the monthly ground flow would vary with the average depletion for the month (Sec. 232 ). Curves of similar import are used by Professor Meyer as a basis for the calculation on ground flow (.Sec. 234). f 2' SUDBURY ^ 7 K. A 6 1 1 1 1 ■4 r t CROTON ~\ 1 1 1 1 1 1 1 NESri/JM/HV/vnD TOHICHON / *2 ■> / 4- S 6 Fig. 289.- Average Month/y Dap/et/on of Ground hfatei — Inches. -Grounds Flow Curves of Eastern Streams. After C. C. Vermuele- 225. Variation in Annual Relations of Rainfall to Runoff. — Taking into account the lag of streamflow due to surface and ground storage, it is not to be expected that any close agreement will be observed be- tween rainfall and runoff for the same period, and the shorter the period and the larger the drainage area, the more discordant the rela- tions which must be expected. Fig. 263, page 443, shows the relations of total annual rainfall to total annual runoff on four streams in which the data for various years are arranged in the order of the magnitude of the annual rainfall. From this diagram it will be seen that in general the annual runoff has increased with the annual rainfall but that in each case there are exceptions more or less radical. In such cases various influences have intervened and have overcome the effects on runoff due to the changes in rainfall conditions. If a diagram be drawn (Fig. 290, p. 497) on which the annual rain- falls be represented by abscissas and the runoff by ordinates, a 45 ° line drawn from the zero point will represent 100% of the rainfall that might run off from a steeply inclined impervious drainage area, such as a slate roof. On account of the various losses which modify and re- duce runoff, the points indicating the relations of annual rainfall to an- nual runoff will fall considerably below this line. If it is assumed that retention remains fairly constant, all observa- Rainfall — Runoff Relations. 497 tions should fall upon a line drawn parallel to the 100% line and at a vertical distance therefrom equal to the average annual retention. In this case the horizontal or vertical distance between the inclined line and the 100% line represents the average annual retention, and the distance from the inclined line to the base represents the varying annual discharges. On this basis, the discharge would apparently be zero should the rainfall equal only the average retention. Where annual rainfalls decrease to this extent, it is found that some runoff usually w y ,# >v AY J v\ 1 Retention (Transpiration, tzraporah an La sf and Deep Seepage) ^^ V -J4^ ■■■ /\ . ..;.-.,' ^ I 'Runoff ^S>\ Annual Rainfall- Inches. A- tjpprox imate Limits of Maximum Runoff o 10 20 so 40 SO /Jnnual Rainfall- Inches. B- Approximate Limits of Minimum Runoff Fig. 290. — Examples of Extreme Annual Rainfall-Runoff Relations, occurs when the rainfall is below the mean annual retention so that the general relations at these lower limits would be better represented by a curved line which becomes tangent to the base line at a point perhaps equal to about one-half the amount of the average annual retention. Long series of observations on many streams show that in general an annual rainfall of at least five inches is necessary to produce runoff even from small drainage areas with mountainous topography, while with broad valleys and gentle slopes, no runoff will occur with an an- nual rainfall of less than than io to 15 inches. This statement is some- what misleading as much depends upon the annual distribution and in- tensity of the rainfall so that the limits named are but roughly ap- proximate. When the annual rainfall becomes more than the mean annual retention there is an increase in runoff more nearly proportional to rainfall and in general this increases with the slope of the area. Curves drawn to represent mean annual rainfall runoff relations will begin with their zero at the limiting annual rainfall at which no runoff will occur and, in general, will run nearly parallel with the 100% line after the rain exceeds an amount perhaps double this limit. Re- Hydrology — 32 498 Variations in Runoff. tention might be expected to increase with rainfall, for the more rain- fall the greater the opportunity for loss through evaporation, trans- piration and deep seepage. The consequence of increased rainfall, how- ever, is high humidity and reduced temperatures which have a tendency to diminish these losses. In general, practical results lie between the one extreme where the normal retention remains almost constant (Fig. 290 A) and the other extreme where the annual retention in- creases with the annual rainfall more rapidly than the increased runoff (Fig. 290 B). In both these cases it is important to note that runoff appears as a residual after the demands of temperature, evaporation and deep seepage are supplied. 226. Approximating Rainfall-Runoff Relations. — Fig. 291 A shows the relation of annual rainfall to annual runoff of the Merrimac River above Lawrence, Massachusetts, for 36 years. The mean rainfall for this period was 41.49 inches, the mean runoff 20.06 inches, and this point is platted on the diagram in the center of gravity of the 36 years obser- vations. The inclined lines on the diagram radiating from the left lower corner indicate the varying percentages of the rainfall appearing as runoff. The average percentage of runoff, is 48.6% of the rainfall but the extreme variations are from 32.2% to 61.9%. Hence, if the discharge had been estimated on the basis of the mean percentage it would have been 51% too high in one case and 21.5% too low in the other. The line of mean annual retention is drawn parallel to the ioo c /o. If estimates of annual flow of the Merrimac River were made on the basis of this line, the extreme variation from actual flow would be 27.5% too high in one extreme and 25.3% too low in the other ex- treme. The latter estimate agrees with the facts somewhat more closely than the percentage estimate but both are considerably in error, and in the consideration of the rainfall-runoff relations of many drainage areas the errors in either method would be much greater than here in- dicated. (Fig. 291 B.) This variation is, however, sometimes well within the limits of the factor of safety which should be allowed in such estimates. If on these diagrams are shown not only the centers of gravity of all observations but also the center of gravity of the groups of observa- tions both greater and less than the mean, rainfall and runoff being con- sidered, lines to represent the mean rainfall-runoff relations with greater accuracy can be drawn through the center of gravity of the en- tire group and approximating the centers of gravity of the sub-groups. The angle of these lines with the base will usually be less than the 45 ° line of Fig. 291 A as is shown by the broken line in Fig. 291 C (after Rafter). Rainfall — Runoff Relations. 499 30 28 26 24 , 22 C/<5 •n te c; /4 <' 2 V /0 o 5 8 | ! / o 'I -"1 / o o / X .' ■^\% nV o Jr* ^~- \ u 7 / / / r* / 15 V o. ^^ rt^ ^. / ' ( * "fv ^3 / / .-- -' / -"' / O 1 . -// >0* / _^L -"" • / y/. -^ y Xx> >i- -' s ' __ -■ c / DC / 1 6° /' . O 1 1° p * 0* , c ^ A f o / 3Ql <■ '/ ,< y - A _. -- " j 12 /6 20 24 28 32 36 40 44 48 52 56 60 64 68 Rain fa// in Inches B. Sudbury River, floss.- /8 75 to /900. / 3 ^ r ^ ^ y o ^ o / o f\0 V O R/i V b / J a* & s 1 + «v ; o K 6*> / / / S / « > ■-' • '. 6 r - 1 ^ ■ ■* s f- "' I /2 /6 20 24 28 32 36 40 44 48 52 56 60 04 6d Rain fa// in Inches C. Croton R/ver, A/ew rork-/877 to /899. Fig. 291.— Annual Rainfall-Runoff Relation on Three Rivers of Eastern United States. 500 Variations in Runoff. Diagrams to fairly represent mean annual relations must differ with various conditions on each particular drainage area and will therefore vary somewhat with every stream. C. E. Grunsky has given the fol- lowing rule for roughly approximating the runoff from a drainage area. "The percentage of the annual rainfall, when less than 50 inches, which runs to the stream, is equal to the number of inches of rain. When the annual rain exceeds 50 inches, 25 inches thereof goes to the ground (evaporation) ; the remainder is runoff." This statement may be useful for readily keeping in mind the general form of a mean runoff curve, but it will hardly be useful for even the rough estimates for which it was designed, except under special con- ditions, as will be noted by reference to Fig. 292 on which the curve rep- resenting this rule is shown (as Curve No. 4) in comparison with other curves suggested by Mr. Grunsky and others for special areas. In this figure are also platted two extreme cases of streams of high and low runoff. Curve No. 1 shows the mean annual rainfall-runoff relations on the Salt Spring Valley. This is a drainage area of 25 square miles tributary to the San Joaquin River and flowing from the west foothills of the Sierra Nevadas in Calaveras County, California. These data were corrected by Lippincott and Bennett 7 for both rainfall and runoff. This curve represents an extreme condition of high runoff. Curve No. 8 shows the mean annual rainfall-runoff relations of Boulder Creek with about 12 square miles drainage area and a mean altitude of 5500 feet above Cuyamaca Reservoir in San Diego County, California. This area represents an extreme condition of low runoff. In both cases the annual relations are also platted on the diagram to show the considerable annual departures from the mean curves. These curves and others shown on Fig. 292 are listed on the diagram, but the annual departures from the other curves are not shown as further data would lead to con- fusion. In examining this diagram it should be noted how widely the observations of individual years depart from the curves which repre- sent mean annual relations and how impossible it is to use such curves as a basis for even approximately estimating the probable annual runoff from rainfall records of areas where different physical conditions obtain Engineers of considerable experience in other matters have sometimes used such curves as a basis for water supply estimates on projects in- e Rain and Runoff near San Francisco, California, by C. E. Grunsky, Trans. Am. Soc. C. E., Vol. 61, p. 514. " The Relation of Rainfall to Runoff in California, by J. B. Lippincott and S. G. Bennett, Eng. News, Vol. 47, p. 467. Rainfall — Runoff Relations. 50 ^ S? Or JS i- (X fe G k "b N OjBj ^ V) H) K OQ «0 \o > CVl C5 «0 ^ > CVi V> VTj ^ ^ j ■tl-:- off. Jan Feb Mar Apr May Jan. Ju/yAugSeptOct Nov Dec // 9/0 8! P $3 Wisconsin River Drainage Area Mean Discharge af Rhmelander Wisconsin Average Mean Rainfall at Seven Stations 1906 -1317 Inclusive ¥ X Z> Runoff JanFeb.fiariAprPttyJunJu/yAug.Sept.Oct Nov Dec ^9 ft s -, ^6 ^3 Coosa River Drainage Area Mean Discharge of Riverside Alabama Average Mean Rainfall af Seven Slat ions IS03- 1313 Inclusive ,o. it's? ' Jan Deb Mar Apr MayJunJu/yAug.SeptOct Nov Dec ^4 Red River of the North Drainage Area Mean Discharge of f\ rargo North Dakota Average fv?eon Rainfal l I \a f fight Stat/ona Jan Deb Mar Apr May JunJu/y Aug Sept Oct Nov Dec. Fig. 293. — Average Distribution of Rainfall and Runoff Throughout the year for Various Streams. 228. Variations in Periodic Rainfall and Runoff Relations. — As would normally be expected from the previous discussion, the rainfall- runoff relations for monthly or seasonal periods are even more erratic than those for the annual period. Temperature and vegetation in- crease with the summer months, and a greater proportion of the rain- fall is lost in evaporation and transpiration and therefore retained from the stream flow. The average seasonal rainfall-runoff relations of four streams are shown in Fig. 293. On the Merrimac River the mean maximum discharge is in April when the winter storage is delivered as runoff, and July, the month of maximum rainfall, has nearly the min- 504 Variations in Runoff. 25 Jan F eb. flar Apr May June Ju/y Auq Sepf Oct Nov Dec. Fig. 294.— Rainfall and Stream Flow for Four Years on the Wisconsin River. imum runoff. On the Coosa River the maximum rainfall and runoff occur in February and March, but the high rainfall of July shows com- paratively little effect on the stream flow. In each case the area below the line of runoff shows the mean annual discharge while the area be- tween the rainfall and runoff curves shows the mean annual retention. Fig. 294, page 504, shows four annual hydrographs of the Wiscon- Periodic Rainfall — Runoff Relations. 505 sin River on which are also platted the mean daily rainfall on the area above the gaging station. The small rainfalls of March which precede the high water periods of April and May should especially be noted. The comparatively small effects of the large summer rainfalls on the flow of such periods should also be noted. In monthly periods the lag of the streamflow and the effect of other factors in general produce very discordant relations between the rain- fall and the resulting streamflow. Runoffs of more than 100% of the rainfall for the monthly periods become common in such comparisons on account of the effect of the rains of previous months. Fig. 295. page 506, is a study of these relations for monthly periods for three small streams near Philadelphia, Pennsylvania. A 45 ° line drawn from the lower lefthand corner of all such diagrams would indicate 100% rainfall-runoff relations, and discharges of more than 100% are found to be common for the first four months of the year. During May to August, inclusive, transpiration and evaporation are at their maximum and the proportion of runoff decreases, but even during May and August single instances are found when the runoff greatly exceeds the rainfall. This is, of course, due to heavy rains near the close of the preceding month and to low rainfalls for the month considered. For October to December, inclusive, the ratio of runoff to rainfall in general again in- creases on account of the reduction in evaporation and vegetable trans- piration, but the relations at best are discordant and not adapted to practical use for even approximate estimates of monthly flow. 229. Rafter's Curves of Periodic Rainfall-Runoff Relations. — Rafter 9 found that monthly relations of rainfall to runoff were too dis- cordant to be used for streamflow estimates, but divided the water year from December 1 to November 30 into the following periods : December-May, Storage Period. June-August, Growing Period. September-November, Replenishing Period. He endeavored to show that when rainfall and runoff are considered for these periods the relations may be fairly Avell represented by curves which may be established for each stream. Fig. 296 is a reproduction of Rafter's diagrams for the Sudbury River rainfall-runoff relations for these three periods. On this diagram are shown, the mean line of retention for the period CC, a more rational line of relation GG drawn approximately through The Relations of Rainfall to Runoff, by George W. Rafter, W. S. Paper No. SO, U. S. G. S., also Hydrology of the State of New York, by George W. Rafter, Bui. 85, N. Y. State Museum. 506 Variations in Runoff. x x Jon uary IV ^° n x f J r cA 2 i c AC* <§§2&''1o * 1 1 l x * AA February _i£k K >e MhA if *i r c A/arch J ^aJ* o ^ A O 9 £0 3* 35 Aq %' ■September o «»?° A * A> 4fA AX ° 1 vLo u «^* n>a i b Apr/7 xa * X - " L ^ii A 3 J„° A o*b p X ■f»TAO 5>f 1 Oc tot er A A 1 I x x *-< *& b of |* o £ &»h 5*1 | ', 1 o rtay o 6 1 " /f *0 1 A \ A °z Aa ¥- >^ &j o i Vc yembsr x X <*: - A - ^ VL< \ — i ^ t? * 1 4 L Uune 1* December A X *£ fl fa M % t* X 2 3 4 5 6 7 8 9 /0 // /2 /3 /4 Rain fa// in Inches Observat ions O / 2 3 4 5 6 7 8 9 /O // /2 /3 /4 Rain fa// /n Inches X Toh/cAon CreeA A A/eshaminy •• O PerA/omen Drai nage Area /02.2 Square Mites. /39. 3 /52. Fig. 295.- -Monthly Rainfall Runoff Relations for Three Small Streams Near Philadelphia. Periodic Rainfall — Runoff Relations. 507 26 24 23 pa 2/ 20 §'? % /7 kt6 % /S 14 /S /2 // W A. Storage Period / e / / /> ' / / //' Center of Gravity 4 /o o (/ $fr or cnr/re uroup X of Su6- Groups vo 3 V 9 / f / / / /o o o ,4 f "I ) L / 3 / ffy / / ' i > / / i f o A / > a s / f c W o C / o ¥ ( / / 6 9/0/1 13 /S /4 /S /S // /8 /S 20 3/ 22 23 24 25 26 27 28 29 30 3/ St _ fpainfa/i fn inches to 6 ^. Growing Ffer/od ,° ^ y 3 / . ^ c ft >r - »J "i£ o .^ / / £^ — «-?* [>•"■ G / u /^J^>5"(5- 7 A? // / £' ( o &' o * -6- / V »/ / S / ^0 /- n <■ -> / ^? *> /. r 1 ^ - ■-H-+-4- Lake Cocihifuctte n l — , , *-f?t?fenf/on Vec / l n -L. 7 ei / - 1" 7 ft , — .._ *crn 1 - — \ 5?>5> 5 5 5 5 5 5 5 Sf 5 5 5 5 $ 83 5 5 $ 5 55 5 5 5 5 ? 5 5 5 ^ 5 5 s> 5 § 5 5 * ? 5 5 5 5 5 5 5 5 5 Si 5 5 5 Fig. 297. — Diagrams of Retention and Temperature for Two Streams in East- ern United States. After G. W. Rafter. to mean temperatures, at least when considered as an independent factor, and that therefore the fundamental bases of Mr. Vermuele's formula are not correct or safely applicable to general calculations of this nature. 233. Justin's Method. — J. D. Justin 4 has suggested an expression for annual runoff in the eastern United States as follows : R2 Fr= 0.934 SOiss — in which F = Annual runoff in inches R = Annual rainfall in inches S = Slope of drainage area found by dividing the maximum dif- ference in elevation on the drainage area by the square root of the drainage area T =Temperature of the drainage area in degrees Fahrenheit Mr. Justin suggests the use of this formula to determine monthly runoffs for the calculation of data for mass curves. Such curves he regards as inaccurate as to individual months but states that such in- * Derivation of Runoff from Rainfall Data, by J. D. Justin, Trans. Am. Soc. C. E., Vol. 77, p. 346. Justin's Method. 513 accuracies will" not affect the conclusions as to the necessary size of the reservoir for a given draft. He believes that the formula is "applicable to the Eastern United States and in general should give results within 10% of the true runoff." His tables, while agreeing more closely with the mean annual runoff of many streams, show a maximum difference in that calculated from the mean annual flow on the Passaic River of 4.6 inches or over 18 per cent, and would evidently vary still more from annual values. Mr. Justin makes no attempt to determine the actual monthly distri- bution of runoff in more than a most approximate way, and the curves representing the expression cannot and do not agree with the observed annual rainfall-runoff relations any closer than the experimental equa- tions of Rafter. He takes into account temperature and slope but neg- lects the ground flow conditions which make it impossible to approxi- mate closely the seasonal variations in flow. 234. Meyer Method. — Professor A. F. Meyer 5 has presented a method of "computing runoff from rainfall and other physical data." In his investigations of northern states, Professor Meyer compares a rainfall year for a 12-month period beginning November 1, with a corresponding runoff year beginning on the following March 1. This method is quite involved and depends upon such a complete knowledge of the physical conditions on the drainage area that ap- parently it is applicable only when more knowledge is possessed than is common in the majority of such problems. Its author has, however, applied it with considerable success to areas where no such detailed knowledge seems possible, such for example as the Ohio River above Wheeling, with 23,820 square miles of drainage area, and the Colorado River at Austin, Texas, with 37,000 square miles of drainage area. The method is made applicable only by the acceptance of certain transpiration, evaporation, soil storage, seepage and surface flow curves which in turn depend upon a detailed knowledge of the peculiarities of flow that have taken place on the drainage area. The transpiration and evaporation curves are based on a consideration of the theoretical factors involved and of various experimental researches and were modified and revised until they gave the best results when actu- ally applied in estimating stream flow. The curves for soil storage, sur- face flow and seepage flow for the calculations of the monthly runoff s Computing Runoff from Rainfall and other Physical Data, by A. F. Meyer, Trans. Am. Soc. C. B., Vol. 79, p. 1056, 1915; also Hydrology, by A. F. Meyer, John Wiley and Son. 1917. Hydrology — 33 5 1 4 Estimating Runoff. of the Root River, in which calculations Professor Meyer's methods are most completely examplified, were derived by their author "not from any group of data but on a process of logical reasoning, experience, ob- servation, and all the facts bearing on the subject which he could com- mand." These curves cannot be reproduced from any data or on any scientific basis. To use this method it is essential to accept these graphical empirical expressions for various constants and modify them on the lines suggested by the author and by the actual runoff relations found to exist on any drainage area to which they are applied, and this cannot safely be done except by or under the direction of an experienced hydrologist. This method was presented as furnishing a skeleton of basic princi- ples, and steps in the computation of runoff to which any degree of re- finement may be applied to the computation by taking into account variations from the normal meteorological conditions on a given drain- age area. The author states that his method should be used "princi- pally for the purpose of analyzing, supplementing and extending ob- served stream flow records so as to make these records a better basis for works of improvement into which runoff enters as a factor." This method presents a distinct advance in the attempt to analyze runoff phenomena inasmuch as all of the principal factors that influence the flow of streams are considered. The disadvantage of this method lies in the necessity of accepting, temporarily at least, certain empirical variable coefficients to be taken from curves which cannot be either verified or corrected except at great labor and after many trials. Its danger lies in their acceptance without verification and their use under conditions to which they are not applicable. 235. Basis of all Methods of Stream Flow ^Analysis. — In general it will be seen that all of the methods which have been suggested or can be devised for analyzing runoff are necessarily the result of correlating observed effects (runoff) and more or less complete data of physical causes (rainfall, evaporation, transpiration, temperature, etc.). The problem is : Given a long detailed record of stream flow together with more or less detailed knowledge of physical conditions, to determine a rational method of applying the known data so that the calculated values of runoff will agree with the observed flow. The object of such methods are : rst. To extend available observations and thus to determine the prob- able effects of more extreme conditions of rainfall, drought and other factors on stream flow. Basis of Stream Flow Analysis. 5 1 5 2d. To enable the engineer to approximate the runoff which will ob- tain from any drainage area where only limited stream flow data are available. Such studies intelligently made possess a great value in familiarizing the engineer with the influence of the various factors on the resulting stream flow, and in extending his knowledge of the stream flow which may have been experienced under extreme conditions which may have occurred but for which no records of flow are available. They are also of importance in the determination of the necessary information to be sought in the investigation of new areas, but they do not furnish a method which can be applied to the solution of such problems for new areas, and their use for such calculations by those who have not made a profound study of the entire subject, is liable to give the results of such calculations a weight to which they are not entitled. At the present time there seems to be no rational method that can readily be applied to the accurate estimate of the seasonal distribution of runoff. In the writer's opinion, when long term records are avail- able comparative hydrographs of adjacent streams should be used and corrected for differences in physical conditions and by at least short time observations on the stream in question. Investigations along the lines suggested by Professor Meyer should also be undertaken to con- firm or correct the opinions so derived. The danger in the use of com- parative hydrographs is evident for the great differences which often occur in the flow of adjacent streams have already been emphasized. Professor Meyer expresses the opinion that comparative hydrographs are of little value for supplementing stream flow data unless the char- acteristics of two drainage areas are identical. While this is true it is also true that calculations for any stream where runoff data are n'ot available cannot be made with any greater degree of accuracy from the characteristics of any other stream unless it has identical characteristics which in turn cannot be determined without extended observations and actual stream flow data. The hydrograph is a correct expression of the detailed runoff of a stream, resulting from all the varying physical conditions which have occurred on the drainage area above the gaging station previous to the time which it represents. It will express the flow of any other stream only when correctly modified for the different physical conditions which have obtained on the comparative area during the corresponding period. The effects of such differences can be only approximately determined, and the comparison is always correspondingly inexact. 5 1 6 Estimating Runoff. 236. Runoff Problems. — In estimating runoff the method employed must necessarily vary with the purposes for which the information is to be used. In general the information sought will involve the total run- off available under certain conditions of storage and distribution. It is evident from a study of the hydrographs previously discussed that there are but few cases in which all of the runoff of a stream can be utilized to advantage under all conditions of flow. The works for the control and utilization of a stream must be built at considerable cost and their size and capacity should be limited so that the returns from the flow conserved will result in an amount adequate to meet with a safe margin, fixed charges, operating costs and maintenance. It is in gen- eral impracticable therefore to develop works of this kind so that they will be utilized to their capacity only once in a long term of years, for the cost will be too great for the benefit received. In some cases where works are comparatively simple and inexpensive and the value of the water conserved is very great, as in the case of public water supplies for large cities, works of sufficient capacity to utilize the total flows of the lowest three to five years may be practicable. In other cases, the practicability may be limited to the total flow of the lowest year. In still other cases the flow which can be made available for the average six to eight months may be the limiting requirement ; while in still other cases the flow which can be made available for the month or week of lowest flow may control. Every case is a special problem which may vary within wide limits and must be solved in some practicable manner, that will give dependable results commensurate with the risk to life, health and property involved. The problems involved may include conditions : 1st. When sufficient runoff data are available, and the information sought is the amount of water which can be utilized with more or less storage. 2d. When no runoff data or only limited data are available, and when the probable runoff must be estimated by comparison with the flow of other streams or calculated from data derived from the flow of other streams. In either case the condition may include problems : A. Where storage is sufficient to equalize the supply over a series of dry years or at least over a series of dry months. B. Where storage is sufficient to improve the average flow of one or two low months. Runoff Problems. 517 C. Where storage is sufficient to improve the flow of the days of low runoff. D. Where storage is only sufficient to impound the low or average day's flow and make it all available during a portion of the day during which it is to be utilized. In many problems of runoff the amount of storage available is a very important consideration. If storage is available sufficient to equalize the flow of a stream for a series of years, a knowledge of the variations in the annual runoff may be of primary importance, and the distribution of runoff during the year may be secondary. If the storage is sufficient to equalize the flow of the lowest year, or even of the one or two lowest months, then the monthly flow may be of primary im- portance and the distribution of flow through the month may be of little importance. In cases of limited storage, where equalization can be accomplished only for a few weeks or a few days, a knowledge of the daily distribution of flow becomes essential. Storage then is frequently an important factor, and the problem may be to determine : a. What storage is necessary to accomplish a certain equalization of flow ; or b. What equalization of flow can be accomplished by a certain avail- able storage. ESTIMATING AVAILABLE FLOW FROM KNOWN RUNOFF 237. Runoff Problems with Large Storage (Flow Known). — Rippl's graphical method of storage computation is of much value where it is desirable to utilize the average flow of a series of dry years or months by storage. This method consists in representing the net yield of a stream graphically by a mass diagram for the entire period for which observations are available or for such special dry periods as will control the extent of the project. From a study of mass diagrams of the net available runoff may be determined : 1. The quantity of storage necessary for its utilization ; or 2. The net flow that can be utilized with a known amount of storage. To use this method of investigation the observed or estimated flow of the stream for each month is reduced by the loss due to evaporation, seepage, etc. The remainder represents the net quantity of water available. The summation of these monthly balances, added one to the other consecutively are then platted in a curve in which the abscissa of 518 Estimating Runoff. each point represents the total time from the beginning of the period ; and the ordinate, the total quantity of water available during the same interval. The scale may represent inches on the drainage area, cubic feet, acre feet, or such other unit as may be desired. Such a curve is represented in Fig. 298, by the irregular curve A-B-C-D-E-F. 600,000 JOO.COO Fig. 298.- Monthj. -Diagram of Rippl Method of Storage Calculations. The inclination of the curve at any point indicates the rate of the net flow at that particular time. When the curve is parallel to the horizon- tal axis, the flow at that time will just balance the losses caused by evaporation, seepage, etc. A negative inclination of the supply line shows that a loss from the reservoir is taking place. In a similar manner the curve of consumption can be platted. For most purposes this can be considered a straight line as the variation in the use of water from season to season is a refinement not usually war- ranted, unless the uses to which it is to be put at various times of the year are well established. In Fig. 298, a series of straight lines of con- sumption are drawn, representing the use of water at rates of 100 to 700 acre feet per day. These rates correspond essentially to rates of from 50 to 350 cubic feet per second. The ordinate between the supply and any demand line represents the Runoff with Large Storage. 5 1 9 total surplus from the beginning of the period considered, and when the inclination of the supply line is less than that of the demand line, the yield of the drainage area is less than the demand and a reservoir is necessary. The deficiency occurring during dry periods is found by drawing lines parallel to the demand line, or lines, and tangent to the curve at the various summits of the supply curve, as at B. The maximum deficiency in the supply, and the necessary capacity of the reservoir to maintain the demand during the period, is shown by the maximum ordinate drawn from the tangent to the curve itself. The period during which the reservoir would be drawn below the high water line is represented by the horizontal distance between the tangent point and the first point of intersection of the curve. If the tangent from any summit parallel to any demand line fails to intersect the curve, it indicates that, during that period, the supply is inadequate for the de- mand. To insure a full reservoir it is necessary that a parallel tangent drawn backward from the low points on the supply curve shall intersect the curve at some point below. For example, the line B-7, representing a daily consumption of 700 acre feet, does not again intersect the curve and is therefore (within the period represented by the diagram) beyond the capacity of the stream. The line B-6 intersects the curve at E and is the limit of the stream capacity. Such a consumption will be pro- vided by a storage of about 115,000 acre feet as represented by the length of the line 6-D, and such a reservoir will be below the flow line for about twenty-two months during the dry period illustrated in this diagram. That this reservoir will fill is shown by the intersection of the lower tangent D-A with the curve near A. The conditions neces- sary to maintain rates of 500, 400, and 300 second feet are shown re- spectively by the tangents B-5, B-4, and B-3, and the verticals 5-D, 4-C and 3-C. If the amount of storage is known, and it is desired to ascertain the maximum demand that can be satisfied by such fixed capacity, the rate is determined by drawing various tangent lines from the summits, hav- ing the maximum ordinates equal to the fixed storage. Mass curves showing the effects of evaporation resulting from various reservoir areas on the available flow of Tohickon Creek are shown in Fig. 89, page 153. The details of the computations on which these curves are based are given in another volume. 6 e Water Power Engineering, by Daniel W. Mead, McGraw-Hill Book Co., 1915, 2d Ed., p. 179. 520 Estimating Runoff. 238. Runoff Problems with Moderate Storage (Flow Known). — When the storage available is moderate in comparison with the runoff available, a method of analysis suggested by Mr. S. B. Hill may be used to advantage. This method is illustrated by an analysis made of the probable available flow of a southern river. Fig. 299 shows the mean monthly flow of the river in question for the years 1893 to 1906 in- clusive. As the higher monthly flows can not be made available the diagrams of flows above 1755 cubic feet per second are not shown. The available storage was 51,000 acre feet or 2,221,560,000 cubic feet, which is equivalent to a flow of 857 second feet for thirty days. The maximum daily continuous flow (A. A. Fig. 299) is determined by the effect of the driest year (viz. 1904) on the storage. The effect of the dry periods on the storage is shown by the indentation into the lower or storage line of the diagram. In the year 1904 the reservoir capacity Avould have been just exhausted in order to maintain the maxi- mum flows during the low months of September, October and Novem- ber of that year. The amount of available continuous flow (i. e. the position of the line A- A) is determined by equalizing the deficiency in flow during the dry months with the total reservoir capacity. It is important in the study of storage to see that in the intervening periods of excessive flow, such flows are sufficient to supply the defi- ciency occasioned by previous demands on the reservoir, otherwise the dry period must be considered in its relation to subsequent periods in determining the available continuous power (see Fig. 299, 1897 and 1898). The daily flow of this river for the year 1904, is shown by the hydro- graph. Fig. 301, from which it will be seen that without storage, the available flow of this stream would be limited to a minimum of 268 acre feet per day. In order to maintain a continuous supply greater than that due to the minimum flow of the stream with storage, some source of auxiliary supply such as wells for water supply or irrigation problems, or some source of auxiliary power such as steam for power developments, must be available. If it is not desired to utilize the flow of the stream to a greater capacity than indicated in Fig. 299 or by a capacity of 1,372 acre feet per day, making the total acre feet available 1,640 (represented by line B-B, Fig. 300), an auxiliary supply or auxiliary power to the extent represented by the double cross hatched areas on this diagram, would be needed. As at all other times water would be available, the addition of steam auxiliary power apparently would be warranted to Runoff with Moderate Storage. £> 1U-4 4- wiff) Storage jA — Q \\^ - ^f "i-W^J __ Fig.' 301. — Hydrograph of a Southern River. of streamflow, it frequently becomes desirable to analyze the probable available flow when the storage is fully utilized or to calculate the amount of storage which will be necessary to accomplish certain re- sults. Under these circumstances it becomes desirable to prepare hydro- graphs of the daily flow of the stream and to analyze the flow from month to month and from week to week in order to determine what the results would have been if such storage conditions had obtained in the past so that the future may be predicted with more or less certainty. In 1917 such an analysis was made of the flow of the Colorado River at Austin, Texas, in order to determine the financial bearing of certain proposed betterments in the dam and power station at that place. 7 In this case almost 20 years of streamflow records were available and daily hydrographs were platted for each year. Each hydrograph included only so much of the flow as might be practically utilized in order that the scale would be sufficiently large to calculate graphically the effect of pondage and the auxiliary power needed to maintain a constant output Report on the Austin Dam, by Daniel W. Mead, City of Austin, 1917. Runoff with Limited Storage. 523 of 3,300 horse power. Fig. 302 shows three of these hydrographs for conditions as follows : A. For the year of maximum runoff, 1900. B. For a year of mean runoff, 1904. C. For the year of minimum runoff, 19 10. The results of the investigations for these years and the means for the entire period for which data were available are shown in Table 51 and also graphically in Fig. 303. TABLE 51 Showing Amount of Hydraulic Power which Could have been Delivered by the Austin Hydraulic Power Plant with a 60-Foot Head and the Normal Flow of the Stream; also the Amount of Auxilary Power Necessary to Maintain 3,300 Continuous Horse Power During Certain Years and for the Mean of the Period from 1898 to 1917, Inclusive. In Thousands of Horsepower Hours 1900 1904 1910 Mean 1898 to 1917 Period Hydrau- lic Steam Hydrau- v lie Steam Hydrau- lic Steam Flydraii- lic Steam February May July September . . . October November .... December .... 2,480 2,240 2,480 2,400 2,480 2,400 2,480 2,480 2,400 2,480 2,400 2,480 1,087 1,050 1,126 1,432 2,480 2,400 2,440 2,240 2,355 2,480 1,260 1,060 1,393 1,270 1,354 968 40 240 45 1,140 1,420 1,013 883 973 2,320 2,267 776 742 736 1,288 1,070 527 533 1.407 1,357 1,507 80 213 1,624 1,738 1,744 1,112 1,410 1,873 1,947 1,397 1,304 1,520 1,831 2,237 2,116 2,073 1,805 1,847 1,857 1,567 1,584 1,083 952 960 569 143 284 407 675 553 623 832 896 Percentage . . . 29,200 100 21,410 7,870 13,123 16,072 21,300 7,920 67.7 32.3 44.9 55.1 72.9 27.1 While this is a special application to the study of a water power pro- ject with steam auxiliary, it is evident that the method used may also be applied to water power or water supply projects where a secondary source with comparatively large pondage may be used as an auxiliary supply. ESTIMATING AVAILABLE FLOW FROM COMPARATIVE HYDROGRAPHS 240. Comparative Hydrographs with Large Storage (Flow Unknown). — The use of comparative hydrographs for estimating the 524 Estimating Runoff. Jan Feb. Mar Apr May June July Aug Sept Oct Nov. Dec. mmmm mmm Y//////////A Seepage.Fvaporation and Pondage Auxiliary Steam Flow of Barton Spring Fig. 302. — Power Hydrographs of the Colorado River. at Austin, Texas (see page 523). ?//, w / ' ' ■ ■ ■ ■ ■ WMWM i^U '/// . . . '//a V/A'//A///Y//X/// y m c .. y/A '///. v-~. „- V-+A V-4/. -.- 1 ,.v „.. &a — / lean Hy< Jrat. 'lie ? ?9"A )s w ''/// - - .... Y//s O 20 \ 40 % <0 60 SO \ s. >s \ •s. \ -n! \ Fig. 303. — Proportion of Yearly Auxiliary Power Necessary to Maintain 3,300 Continuous Horse Power on Colorado River at Austin. (See page 523.) Comparative Hydrographs. 525 flow of a stream where little or no runoff data are available is consider- ably simplified when large storage is practicable. During 1918 it became desirable to determine the probable amount of runoff of the Ashtabula River near Ashtabula, Ohio, that could be utilized for power purposes by the construction of certain reservoirs on the drainage area. There were no stream flow measurements available from the drainage area, hence it became necessary to estimate the probable runoff from the com- parative runoff of other streams. r. Comparative Drainage Areas. There were available for com- parative purposes runoff measurements on nearby streams as follows : Steam Location Area Sq. Miles Data Available Shenango River. . Cussewago Creek. Shenango River. . Shenango River. . French Creek French Creek Sharon, Pa Near Meadville, Pa Greenville, Pa 610 90 152 107 1-1-1910 to 1-1-1918 6-1-1910 to 1-1-1918 2-1-1912 to 1-1-1918 1-1-1914 to 1-1-1918 5-1-1910 to 1-1-1918 5-1-1910 to 1-1-1918 The records of the last two stations were defective as the rating curves were not well defined. The published data for French Creek at Kimmeytown indicated annual runoff almost equal to the annual rainfall, thus showing their unreliability. These two streams were also at a considerably greater distance from the Ashtabula River than the first four, so that the data from the first four streams were used in the computations. Fig. 304 is a map of the region adjacent to Ashtabula, showing the relative location of the Ashtabula River and of the four drainage areas used as a basis for comparison, and also the location of the nearest sta- tions where rainfall records were available, viz., at Erie, Saegerstown and Greenville, Pa., and at Warren, Hillhouse and Cleveland, Ohio. Without considering the area of the reservoirs, the drainage area above the lower proposed reservoir dam on the Ashtabula River was 116 square miles. For safety this was estimated at 100 square miles, thus making an allowance for safety of i6°/o on runoff calculations. 2. Reservoir Capacity. In considering the development proposed, it seemed to be practicable to construct reservoirs having a total usable capacity of 1,589,500,000 cubic feet, and the estimates were made on this basis. 526 Estimating Runoff. 3. Mass Curves of Runoff. Mass curves of each stream (Fig. 305) showing the accumulated sum of the monthly runoffs in cubic feet per second per square mile were first platted, and the rates at which the water could be used were then determined. The rate lines are the in- clined lines shown on the diagrams and begin in each mass curve at various dates when the reservoir can be considered as filled. The slope of these rate curves is determined by two requirements : 1. The capacity of the reservoir. 2. The requirement that the reservoir must be full at the close of the period. 'eteger'sfown Fig. 304. — Region of the Ashtabula River and Comparative Drainage Areas. (See page 525.) The capacity of the reservoir is indicated on the drawing by the height of the vertical lines drawn near the center of the rate lines and near the middle of the periods of deficient stream flow. The vertical lines which occasionally appear at the end of one rate line and at the beginning of another show the amount of water which would reasonably have been wasted for lack of greater reservoir capacity. The rate lines at the end of December, 19 17, are drawn so as to leave the reservoirs at that date partially filled to provide for partial deficiency at the beginning of 1 9 18, although the runoff records show that the streamflow during the Comparative Hydrographs. 527 first three months will probably fill the reservoir, in addition to supply- ing water for a fair rate of use. 4. Estimates of Usable runoff. — The results of the computations for mean monthly runoff are shown on the mass curves and are summarized in the following table : TABLE 52 Regulated Mean Annual Flow of the Ashtabula River in Cubic Feet Per Second Per Square Mile (with Storage) Based on the Actual (Regulated) Floio of Comparative Streams. River Above Shenango Sharon Pa. Shenango Turnersville, Pa. Little Shenango Greenville, Pa. Cussewago Meadville, Pa. 610 sq. mi. 1.26 1.35 1.62 1.25 1.06 .99 1.06 1.10 152 sq. mi. 107 sq. mi. 90 sq. mi. Year 1910 1911 1.75 1912 . 1.58 1.39 1.22 1.24 1.17 1.39 1.64 1913 1.33 1914 1.18 l.o3 1.24 1.18 1.21 1915 1.19 1916 1917 1.20 1.20 Mean 1.21 1.33 1.23 1.36 Mean of all records 1.285 5. Hydrographs. — The hydrographs (Fig. 306) were also made on the basis of the average monthly runoff in cubic feet per second per square mile. The use, storage and waste of water is also indicated by the shaded areas. This shows in a different way how the flow could be utilized. This form of diagram if drawn to a large scale on cross sec- tion paper may also be used in calculating the available stream flow by making the water used during the dry period equal the excess runoff. This method is ordinarily less accurate and does not so clearly indicate the limiting effect of storage. The average of all the records of mean annual flow for these streams is 1.28 cubic feet per second per square mile. 6. Geological Conditions. — In general the drainage areas of all the streams in question are covered by drift varying from 25 to 75 feet in depth. The underlying indurated formations are not known in detail, but the entire Ashtabula River drainage area lies within the area of Devonian shales, while the other stream areas lie almost entirely within 528 Estimating Runoff. an area of carboniferous limestones, sandstones, conglomerates and shales. Normally it would be expected therefore that the flow of the Ashtabula River would be somewhat greater than that of the other streams for the character of the underlying deposits of the four com- /9/0 1911 /9/2 /9/3 /9/4 /9/5 (9/6 /9I7 Fig. 305. — Mass Curves of Runoff of Various Streams near Ashtabula, Ohio. (See page 526.) parative streams would probably lead to some losses from deep seepage which would not occur on the Ashtabula drainage area. 7. Rainfall. — To determine the distribution of the annual rainfall for the eight years for which runoff data were available, maps were drawn (Fig. 307) on which were platted isohyetal lines, for the water Comparative Hydrographs. 529 /9/3 /S/6 ~ '. >'>''.'7? T V//// m^ Re /a t/ve Discharge, L i / //e Shenango River at Greenv///e, Pa. Re/a /ive Discharge, Shenango River at Turner ■i/i/Ze, Pa. Re/a five Discharge, Shenango R/ver at Sharon, Pa. Re /a// ye Discharge, Cussewago Creek near r/eadvi/Ze, Pa. Fig. 306. — Comparative Hydrographs of Streams near Ashtabula^ Ohio. (See page 527.) Hydrology — 34 530 Estimating Runoff. A. indicates Drainage Area of Ashtabu/a PiVer near Ashfabu/o. Oh/o. C- indicates Drainage Area of Litt/e Shenango Piver af / ■ ' ° * •<■ ,& -y t S > ■ , / ? - 4, / / E 16 14 12 10 r 1 \ Shenango f?iver Turnerr/He, Pa. r /- Y> W y y 6 /, / ■ E 50 36 3d 40 42 44 46 48 50 36 38 40 42 44 46 Pa/'n foil I -Inches on Drainage Area. Fig. 310. — Mean Annual Rainfall-Runoff Relations for Streams near Ashtabula, Ohio. (See page 532.) plant, which, together with the auxiliary power already installed, would maintain the total output to an economical maximum which the flow of the more productive year might warrant. 12. Method. — The method of estimating runoff by comparison with other streams as outlined above is evidently open to criticism as ap- proximate and subject to considerable errors. It is believed, however, that the factor of safety used resulted in a conservative and safe esti- mate of runoff. This method offers a fairly definite method of proce- 536 Estimating Runoff. dure which can be applied without radical assumptions and by engineers of limited hydrological experience. When time and expense are war- ranted, this method can and should be supplemented and the conclu- JFig. 311. — Relative Locations of Drainage Areas of the Peshtigo, Wisconsin and Menominee Rivers (see pagee 538). sions corrected by at least short time observations of streamflow on the stream for which the estimates are made. It is also probable that a more detailed analysis of the monthly rainfall-runoff relations, some- what on the line of the Meyer method, might serve to confirm or cor- rect the conclusions drawn. Comparative Hydro-graphs. 537 M ina'/cates Drainage Area of Menominee Pi ver P indicates Drainage Area of Peshtigo Piyer. Wind/cafes Drainage Area of Wisconsin Piver Fig. 312. — Annual Rainfall on Drainage Areas of Peshtigo, Wisconsin and Menominee Drainage Areas (see page 538). 241. Estimating Available Flow with Moderate Storage from Comparative Hydrographs. — In the year 1906 investigations were be- gun on the feasibility of developing the Peshtigo River of Wisconsin at High Falls (see upper Frontispiece) for power purposes and con- 538 Estimating Runoff. ducting electrical current to Green Bay to be used, with the stream electric plant already installed as auxiliary, for the purpose of furnish- ing power and light to that City. Surveys were made from Johnsons Falls (about y/i miles below High Falls) to Cauldron Falls (about yy 2 miles above High Falls) and as the project looked favorable, a gaging station was established near a farm house 9 miles below the dam site. In 1908 the question of construction became important and es- timates of the probable flow of the stream became necessary. At the time this estimate had to be made there were one year's gagings available on the Peshtigo River and about five years' gagings on the Wisconsin River at Merrill, and on the Menominee River near Iron Mountain, Michigan. 1. Physical Conditions. The relative locations of the drainage areas of these streams are shown on the map (Fig. 311). All of the areas considered lie within the boundaries of the kettle moraine of the second glacial period and within the geological limits of the Archean and Al- gonquin Rocks. The Wisconsin drainage area has the greatest amount of surface storage in lakes and swamps and considerable deposits of sandy soils of the second glacial epoch are found on all three drainage areas. 2. Rainfall. — The distribution of the annual rainfall for the water year beginning Dec. 1 and for the five years for which runoff records were available and the mean annual rainfall for the years preceding 1908, are shown on the series of maps in Fig. 312. From these maps the mean annual rainfalls on each drainage area for each year, for the mean of the five years of runoff records and for the mean of the period of rainfall records were determined and are shown in Table 55. TABLE 55 Mean Annual Rainfalls on Peshtigo River and Comparative Drainage Areas. Drainage Areas 1903 1904 1905 1906 1907 5- Year Mean Mean Annual Rainfall Wisconsin 42.1 46.5 46.5 34 36 39.5 34.5 36 39.5 36 38 39 24.5 27.5 32 34.2 37.3 38.2 * 27.2 33 Menominee 32 The average annual rainfalls at certain stations adjacent to the three drainage areas considered are shown in Fig. 313, page 539. Estimating from Comparative Hydrographs. 539 "> ^» **> *o <3 5 <5 <5> O) ft) Dj 1) O) . /lean Annua/ Annuo/ and Seasonal Roinfo// on one/ near /he r*Tenominee River Drainage Area /lean Annua/ r/ean S/ or age r/eon Growing Mean Pep/enishing Annua/ and Seasona/ Ra/nfa// on and near /he Wisconsin River Drainage Area /lean Annual /lean S/orage /lean Growing /lean Rep/enishing Annua/ and Seasona/ Rom fa// on and near /he Resh/igo River Drainage Are a I | S/orage Period v%A Growing Period Uli Pep/enishing Period Fig. 313. — Annual Rainfall at Stations on the Peshtigo, Wisconsin and Menom- inee Drainage Areas (see page 538). 540 Estimating Runoff. 3. Runoff. — A comparison of the hydrographs of the Peshtigo, Wis- consin and Menominee Rivers, showing the discharge in cubic feet per second per square mile for the year 1907, is shown in Fig. 283, page 487. <0 \ \ 1 v I \ V V \ A , \ 1 V \ \ ^ Os. -v Its.- V ~>G--Z?o Y&o~: ,, -<-'i? — " ~["g a. b^r: — V—-. ^"*^H^_ ~~~**~ ' s / ff— Comporati ve Duration Curves for /907 I \ w ^ \v\ s \ \\ s V \ -X \ ^ \to *^&h~ 1 ^ N ~~^: : -k. [■ ^^ 1 \ \ V* - ,._ ~* — ^&~ — - ~-~_ ^S&r>> "^^Tj^^ j^Sr - "~~~ -J*^^- t~^r--^ ^306 t — =^ — --H^,. — — --i r.--^ B.- Duration Curves of the Menominee River \ ^^ \ 1 \ \ '- "^"^ > 'OS ;» V ■.\" x --... /r> x ^V ^pjt ~~~ ^ v ^ ^~ _ *£?oe ^\\^ \ ^-^ =■ \ , - — is ■*. *~^. =^-— -•-». =xo "~ , "*£?5*j ^ ~---- ^TKP ^^ 1 — =■ x -«^--- ^^ ~» ^ — -.v C.~ Duration Curves of the Wisconsin River Fig. 314. — Duration Curves of the Peshtigo, Wisconsin and Menominee Rivers. From these hydrographs, corrected for flow under ice conditions, the comparative duration curves for these three rivers and for the year 1907 were made (Fig. 314-A). These duration curves show the same data as shown by the hydrographs (Fig. 283) except that the daily runoffs are shown arranged in the order of their magnitude. With Estimating from Comparative Hydrographs. 541 the storage available above High Falls, these curves would all be main- tained to a minimum of .645 cubic feet per second per square mile. As the annual rainfall on the Peshtigo drainage area for the year 1907 was a minimum for the 16 years of annual rainfall records, and about 10% below the mean annual rainfall on the drainage area, it seemed probable that the flow of that stream for that year reaches a minimum that would rarely be reached. It should also be noted that although the annual rainfall for 1907 on the Peshtigo River was 10% less than on the Wisconsin and 23% less than on the Menominee, the low water flow for the lowest six months of the year was well maintained and only slightly less than that of the two comparative streams. Comparative hydrographs of both the Wisconsin and Menominee Rivers were also made and studied. The daily hydrographs for the Menominee River are shown in Fig. 315. Duration curves for both streams for the five years of records are shown in Figs. 314. The rainfall diagrams of Fig. 313, and the Table 55, both show that the annual rainfalls for 1903, 1904, 1905 and 1906 on both the Wisconsin and the Menominee drainage areas were considerably above the mean annual rainfall for the period of rainfall records, but that the annual rainfall for 1907 on both areas was much less than the mean and very near the minimum for the period of record. 4. Conclusions. — It was concluded from this study that the average flow would probably be at least 10% greater than shown by the 1907 hydrograph and duration curves ; that there might be years of somewhat less flow which could be cared for by the Green Bay steam plant ; that the hydrograph and duration curve of the Peshtigo River for the year 1907 furnished a conservative basis for estimating the average annual available water supply ; and that if such as an average would furnish an amount of power which would be profitable when the cost of installa- tion and operation was considered, then the project was feasible. The final conclusions were that a dependable average flow of 377 second feet was available which with the 85 foot head, which could be de- veloped, would at 80% efficiency produce at the turbine shaft 70,000 horse power hours per day, and that with the steam auxiliary power available at Green Bay it would pay to develop the hydraulic plant to to a capacity of 485 second feet or 90,000 horse power hours per day. It may also be noted that the plant at High Falls was duly constructed (see Frontispiece, lower figure) and has been operated successfully and profitably. A hydrograph showing the natural stream flow, the water used and the water wasted, as well as the variations in head in the reservoir for the year 19 17, is shown in Fig. 278, page 475. 542 Estimating Runoff. Jan. Feb. Plan Apr. rloy .June Ju/y Aug. Sept, Oct. A/ov. Dec. Fig. 315. — Hydrographs of the Menominee River (see page 541). Literature. 543 LITERATURE Rainfall and River Outflow in the Mississippi Valley, Thomas Russell, Ann. Rept. Chief Signal Officer U. S. A., 1889, Pt. 1, Appendix 14, p. 159. The Laws which Govern Stream Flow, C. C. Vermuele, Geol. Survey, New Jer- sey, Vol. 3, Water Supply, 1894. Forests and Water Supply, C. C. Vermuele, Ann. Rept. State Geol. Survey, 1899. Stream Floio Data from a Water Power Standpoint, C. E. Chandler, Jour. N. E. Water Wks. Assn., Vol. 21, p. 464, 1907; also Vol. 22, p. 409, 1908. Power Capacity of a Running Stream with Storage, W. G. Raymond, Jour. N. E. W. Wks. Ass'n, Vol. 22, p. 184, 1908; also Proc. Iowa Eng. Soc. 17th Ann. Meeting, 1905. Derivation of Runoff from Rainfall Data, J. D. Justin, Trans. Am. Soc. C. E., Vol. 77, p. 346, 1914. Computing Runoff from Rainfall and other Physical Data, A. F. Meyer, Trans. Am. Soc. C. E., Vol. 79, p. 1056, 1915. Poioer Estimates from Stream Flow and Runoff Data, D. M .Woods, Boston Soc. C. E„ Vol. 3, p. 77, 1916. STORAGE AND PONDAGE The Capacity of Storage Reservoirs for Water Supply, W. Rippl, Pro. Inst. C. E„ Vol. 71, p. 270, 1883. Storage and Pondage of Water, J. P. Frizell, Trans. Am. Soc. C. E., Vol. 31, p. 29, 1894. A Mathematical Analysis of the Influence of Reservoirs upon Stream Flow, J. A. Seddon, Trans. Am. Soc. C. E., Vol. 40, p. 401, 1898. The Croton Valley Storage, Samuel McElroy, Jour. Assoc. Eng. Soc, Vol 8, 1889. Flow of Streams and Storage in Massachusetts, Desmond Fitzgerald, Trans. Am. Soc. C. E„ Vol. 27, p. 253, 1892. Rainfall, Flow of Streams and Storage, Desmond Fitzgerald, Am. Soc. C. E., Vol. 27, p. 304, 1892. Storage Reservoirs in Southern Cal., Robert Fletcher, Eng. News, Vol. 46, p. 124, 1901. Pondage and Storage, D. W. Mead, Chap. VII, Water Power Engineering, McGraw-Hill Book Co., 1915. Reservoir System of the Great Lakes of the St. Lawrence Basin, Its Relation to the Problem of Improving the Navigation, H. M. Chittenden, Trans. Am. Soc. C. E., Vol. 40, p. 355, 1908. Effect of Proposed Storage Reservoir on Stream Flow and Water Power of Lower Chippewa River, C. B. Stewart, Eng. News, Vol. 70, p. 246, 1913. Storage to fee Provided in Impounding Reservoirs for Municipal Water Supply, Allen Hazen, Trans. Am. Soc. C. E., Vol. 77, p. 1539, 1914. Filling and Emptying Reservoirs, T. R. Running, Graphical Solution, Eng. Rec, Vol. 69, p. 67, 1914. CHAPTER XIX FLOODS AND FLOOD FLOWS 242. The Importance of Flood Studies. — The problems of flood relief with which the engineer has most commonly to deal are the pro- tection of populous districts of cities by the construction of storm water sewers, and the drainage of agricultural lands by canals and ditches. Closely connected with such works are the design and construction of channel improvements and levees for the protection of city and agricul- tural areas from the flood overflow of creeks and rivers bordering on or passing through areas to be protected or improved. Still greater problems arise when important communities must be protected from the damages occasioned by great floods where conditions must be im- proved by still more comprehensive works, including river diversion and training works, channel improvements, levees and revetments and perhaps the construction of impounding and retarding reservoirs. The railroad engineer finds constant need for the study of flood con- ditions in order to design the culverts and bridges frequently necessary along the railroad rights of way, with sufficient capacity and stability to protect tracks and embankments from washouts and .the attendant re- sults. In water supply, water power and irrigation work the engineer must often design structures to impound, conserve and utilize water supplies, and must provide suitable spillways, wasteways and flood gates to pass the occasional high flood flows in order to protect such structures and the lives and property of the communities lying in the valleys be- low. Such works are rapidly increasing in number and importance with the growth and development of the country, and the consequences of ignoring flood conditions, of understimating flood intensities or of improper designs to meet the contingencies of floods are constantly becoming more serious and involving almost yearly great losses in prop- erty and occasionally large losses in life. 243. Changing Conditions and Flood Effects. — In general the flood plains of streams have been created by the streams themselves and channels have been maintained only commensurate with the normal floods which annually flow through the channels. The occasional high flood overflows the river banks, the extreme flood which occurs only at rare intervals may find the channel entirely insufficient (Table 56) and overflow the entire flood plains from hill to hill. (Fig. 316.) In the Flood Effects. 545 TABLE 56. Present Channel Capacities in the Cities of the Miami Valley Compared with the 1913 Flood Discharge.* City Channel Capacity Sec. Feet Flood Discharge Sec. Feet Ratio Per Cent Drainage Area Sq. Miles Sidney Piqua Troy Dayton Dayton (Below Wolf Creek) Miamisburg Franklin Middletown Hamilton 10,000 25,000 20,000 90,000 100,000 65,000 65,000 115,000 100,000 44,000 70,000 90,000 250,000 252,000 257,000 267,000 304,000 352,000 22.7 35.7 22.2 36.0 39.7 25.3 24.3 37.8 28.4 555 842 908 2,525 2,598 2,722 2/7.85 3,162 3,672 7dO 770 76(? _ River Channel ff.— Cross 5ecf/on of Miami River at Dayton, Ohio City of Dayton D/Afance-3 - Hundreds of feet: 30 Fig. 316. — Extent of Overflow from the 1913 Flood. a Report of Chief Engineer, Miami Conservancy District, Vol. 1, p. 26, 1916. 2 Diagram A from Eng. News, Jan. 4, 1917. Diagram B from Rept. Chief Engr., Miami Conservancy Dist., Vol. 1, p. 68, 1916. HYDROLOGY — 35 546 Floods and Flood Flows. settlement of every country the lands first occupied are those that are most convenient and favorable for habitation, agriculture, commerce, manufacturing and other uses. Submerged lands or lands subject to frequent overflow are at first ignored, and those subject to occasional overflow may be settled and be abandoned when such overflow occurs, or are occupied on account of their otherwise desirable character or location in spite of the occasional troubles and losses entailed. t Pig. 317. — Gully Erosion near Janesville, Wis. As communities develop, the existing settlements attract other set- tlers and the demands for additional area for habitation, manufacturing and agriculture increase land values. Channels that are only occasion- ally occupied by the streams and low bottom lands are filled and built upon ; bridges are built often without provision for extreme floods ; and even the normal channels are sometimes so restricted (Fig. 276, page 465 ) that the ordinary floods must rise in height in order to create the increased velocity needed to carry the water through the reduced chan- nel. In many cases the channels of streams through farming districts become restricted to a greater extent than those through cities. Im- proper methods of cultivation and the diversion of minor drainage to new channels often result in undue erosion (Fig. 317) and cause the washing into the streams of large quantities of sands and gravels which congest the channels (Fig. 318). Caving banks carry stumps and trees into the stream, and the channel is also frequently used as a convenient Flood Effects. 547 Fig. 318. — Bar Formed in the Rock River above Janesville, Wis., due to Erosion shown in Fig. 317. dumping ground. The result is undue congestion which often becomes manifest only under extreme flood conditions (Table 57). TABLE 57. Present Channel Capacities at Yarious Loations in the Miami Valley Out- side of Towns and Cities, Compared with the 1913 Flood Discharged Stream Location Channel Capacity Second Ft. Flood Discharge Second Ft. Ratio Per Cent Mad River Mad River Stillwater River. Stillwater River . Stillwater River. Loramie Creek . . Miami River Miami River Miami River Miami River Miami River Miami River Miami River Miami River Twin Creek .... West of Springfield . Below Osborn Above Covington . . . Below Covington . . . Above West Milton . N. W. of Lockington Above Sidney Above Sidney Below Piqua Tadmor Below Dayton Below Miamisburg . . Below Hamilton Below Miamitown West of Germantown 5,000 6,500 1,200 6,000 7,000 1,600 5,000 5,000 10,000 8,000 25,000 35,000 25,000 20,000 3,000 55,400 75,700 33,100 51,400 86,200 25,500 34,100 48,500 70,000 127,300 252,000 257,000 352,000 384,000 66,000 9.0 8.6 3. 11. 6.3 14.7 10.3 14.3 6.3 9.9 13.6 7.1 5.2 4.5 3 Report Chief Engineer, Miami Conservancy District, Vol. 1, p. 25, 1916. 548 Floods and Flood Flows. 244. Great Floods and Flood Losses. — The damages occasioned by floods are notable on account of their sudden and serious character, and while it is probably true that the financial losses occasioned by floods are not in the aggregate so large as those occasioned by droughts yet the latter are less obvious or determinable and in general more difficult to prevent. Floods destroy property and life, and losses are direct and measurable. The effects of their recurrence and often of their first occurrence can be obviated by proper protective measures, al- though in general the shortsightedness of a community in this regard is overcome only after actual flood losses have been experienced. As examples of the serious nature of flood problems and the neces- sity of betterments to prevent the recurrence of such disasters, the following data are given concerning a few floods of comparatively re- cent times. 4 In 1791 Great flood occurred in Cuba and some 3,000 lives are said to have been lost. In 181 1 Some 24 villages were swept away by a great flood of the Danube in Hungary. In 1813 Some 10,000 lives were lost by floods in Austria, Hungary, Poland and Silicia. In 1824 Ten thousand lives were lost in St. Petersburg and Cron- stadt from a flood of the Neva. In 185 1 The Yellow River of China burst its banks and changed its course for almost 600 miles, changing its point of discharge from the Yellow Sea to a point 200 miles north in the Gulf of Chili. In 1856 Flood damaged the south of France to the extent of $28,000,000. In 1874 One hundred forty- four persons were drowned by a flood accompanied by the bursting of a dam on Milk River, Mass., and 220 lost their lives in floods in Western Pennsylvania. In 1889 Much of Johnstown, Pennsylvania, was destroyed by a flood which broke the dam on the Conemaugh River, many lives were lost and property worth several million dollars was destroyed. In 1903 A great flood occurred in Kansas City and on the Mississippi River, causing a loss of many millions of dollars. Heppner, Oregon, was also destroyed with a loss of about 300 lives. In 1910 The Seine flooded Paris and caused a loss of over $200,000,000. In 191 1 A flood in Freeman's Run caused the failure of a storage * Floods — Encyclopedia Americana. Flood Losses. 549 92° 9/° 9CT 89" Fig. 319. — Alluvial Flood Plain of the Lower Mississippi River (see page 550). 550 Floods and Flood Flows. dam with the loss of 87 lives and the destruction of most of the Village of Austin, Pennsylvania. Extensive floods causing heavy losses were also experienced on various rivers in Wisconsin. In 191 3 Great floods occurred in Eastern United States. In the great Miami Valley about 400 lives were lost and property valued at about $100,000,000 was destroyed. The history of the great plains of China from Peking to the Yangste River for the last four thousand years is replete with the occurrence of floods in which have been lost literally many millions of lives. The history of the settlement of the lower Mississippi Valley is a continued story of loss of life and property by the almost yearly overflow of that river. In some cases floods have been accentuated by the sudden re- lease of stored waters from improperly designed dams and reservoirs, and occasionally this has been the controlling cause of the great loss of life and property. Much can be done toward alleviation and prevention of these condi- tions by intelligent engineering works if supported by enlightened pub- lic opinion. The great increase in these losses with the development and growth of the country is creating a constant demand for such betterments. 245. Floods of the Lower Mississippi Valley. — The greatest flood problem in the United States is that of the Lower Mississippi Valley. (Fig. 319.) This great valley on account of its accessibility by navi- gation, its fertile flood plain and temperate climate attracted settlement at an early date. The settlement of these lands and their frequent inundations by the floods of the river have caused almost annually great losses in property and frequent losses of life. This resulted in early attempts at local betterments which have Jater been organized into more consistent efforts through state and district levee boards and later by government assistance through the Mississippi River Com- mission. The total amount expended on the levees of the lower Mississippi up to 19 14 was about ninety-seven million dollars of which the United States expended thirty-one millions. Up to June, 1913, the total ex- penditures of the United States on this portion of the river was about seventy million dollars. 5 The early works of protection were limited in extent and the levees were only sufficient for protection against moderate floods. Even at the present day the levees have not been • r ' Hearings on Bill S. 2, To prevent floods on the Mississippi River, Commit- tee on Commerce, U. S. Senate, 63d Cong., 2d Session, pp. 137-175. Lower Mississippi Valley. 551 built to an elevation sufficient to provide for the maximum flood height which must be expected when the works are finally completed and rendered permanent by proper revetment and other bank protection. The occasional great floods obtain at intervals averaging about once in six years (see Floods of +50 feet at Cairo, Fig. 320), although it will be noted that they sometimes follow each other annually for two or three years. These great floods have frequently destroyed miles of levees and inundated great sections of the alluvial valley. The area of the alluvial flood plain of the Lower Mississippi subject to overflow 60 SO ML 1 55/5S/pp/ 1 River erf Ca/ra,. r//. IJl . 1 II Il 1 ill 1 II 1 U 9 H h n n 1 U 1 i 9 1 E 1 1 1 11 1 1 ^0 y° /0 ~/8Z0 /830 '840 J850 /860 /870 /880 /8.90 1900 1910 /920 Fig. 320. — Maximum Annual Gage Heights on the Mississippi River at Cairo, 111. prior to the construction of the levee system is estimated by the Missis- sippi River Commission at 29,790 square miles (Fig. 319). The flood of 1897 inundated 13,578 square miles and that of 1913 about 10,812 square miles. The ordinary floods of the Lower Mississippi are caused by the normal floods of its various tributaries, the Upper Ohio, the Tennessee, the Upper Mississippi, the Missouri Rivers and many minor streams. When the normal spring floods on these various tributaries fail to synchronize near their crests the floods on the lower river reach only normal heights, but where exceptional rains produce high flood condi- tions on one or more of these tributaries and these floods synchronize with ordinary floods on other tributaries, exceptional floods result in the lower river. The heights of the maximum annual floods at cer- tain stations on the Mississippi River and its tributaries are shown in 552 Floods and Flood Flows. J\ P ?«\ \ Ni\ r lK '1 N -^Ci pyf H ! r — X \ 1 N / ! ^ri \j y^ ^)V^~ )i / ( i \ ) i / ' ' / \ Floods in Wisconsin. 553 Figs. 320 and 327. The relative gage heights at various stations on the tributaries, and the resulting gage heights at Cairo, are shown in Fig. 326, and the rainfalls producing the flood of 1882 together with the departure of the rainfall from the normal are shown in Fig. 321. 246. Floods of October, 191 1, in Wisconsin. — The autumn flood of October, 191 1, on the Wisconsin River was one of the most severe on record for that river. In general floods on the Wisconsin occur in the spring (Fig. 327, p. 562). When fall floods occur they are always due to a saturated condition of the drainage area from earlier rains followed by an unusual intense concentrated rainstorm. In this case the rainfall of October 2 to 6 was preceded during the thirty days from September 3 to October 1, 191 1, by a somewhat heavy pre- cipitation, the distribution of which is shown in Fig. 322 A. The heaviest rainfall of October 2 to 6 extended across the upper portion of the Black River Valley and as a broad band across a portion of the Wisconsin River Valley (Fig. 322 B)) The heaviest portions were south of the headwaters of the Wisconsin River (see also Fig. 200, P- 339) where a reservoir system has been constructed. The progression of the flood wave from this storm is shown by hydrographs for different points along the Wisconsin River in Fig. 287, p. 493. At Rhinelander, above which most of the reservoirs on the river are constructed, there was practically no flood. In this flood a dam just below Wausau went out (Fig. 5, p. 27) which undoubtedly was one of the causes of the extra rise at Knowlton. At Grand Rapids the flood peak followed a little later. Some of the flood gates at that point were blown out which added somewhat to the flood heights below that point. At Prairie du Sac, where the plant of the Wisconsin River Power Company was under construction, the work was flooded, the cofferdam destroyed and a large loss entailed. The greatest flood loss from this storm occurred on the Black River. The first casualty was the failure of the earth dike of the Dells reser- voir dam. This reservoir was used for storing water for power pur- poses and impounded about 10,000 acre feet. The dam consisted of a concrete section and spillway and of an earthen dike with a concrete core wall. The break was occasioned by the over-topping of the earth section due to inadequate spillway capacity. The concrete section was left intact but the earthwork with i.ts core wall was destroyed. The failure of this reservoir resulted in the overtopping of the earth section of the reservoir at Hatfield, about 4}^ miles below. The Hatfield dam consisted of a concrete spillway about 50 feet in height on both sides of which was an earth embankment. The spill- 554 § Floods and Flood Flows. "o vo Floods in Wisconsin. 555 way which was some 490 feet long was adequate for any normal flood in the river and passed about 12 feet of water before the east embank- ment was overtopped and destroyed. The flood waters, when they passed over the earth section, washed out 500 feet of reservoir em- bankment and about the same length of the Green Bay and Western Railroad which crossed the Black River at this point. A view of the site of the destroyed earth section at Hatfield, taken some time after Fig. 323. — Break in Earth Embankment at Hatfield Dam. the flood, is shown in Fig. 323, and the water from these reservoirs together with the normal flood of the Black River sweeping down on the City of Black River Falls about 12 miles below Hatfield, caused great damage in that city. The dam at Black River Falls during the flood of June, 191 1 (Fig. 324), carried about 10,000 cubic feet per second with the spillway more than filled. A normal high flood flow of about 40,000 cubic feet per second must be expected at Black River Falls under extreme con- ditions and without floods from breaking reservoirs. The north abut- ment of this dam entered a natural bank of earth but did not reach rock (Fig. 192, p. 333). The October flood perhaps 80,000 second feet, cut entirely around the north end of the dam and overflowed the business district of the City. The view of the flood entering the city (Fig. 325) shows a three-story hotel with a portion of its walls just 556 Floods and Flood Flows. Flood Problems. 557 falling into the river. The buildings in the business portion of the city* resting on sand foundations, melted into the stream and disap- peared, and the flood destroyed not only the buildings and their founda- tions but the land was entirely washed -away for about two blocks in width and for several blocks in length (Fig. 194, p. 334). The wooden mill building (Fig. 325) which rested on a rock foundation was not seriously injured. Perhaps the best understanding of the nature of Fig. 325.— Flood of October 1911 Entering the City of Black River Falls. the catastrophe can be gained from Fig. 193, p. 334, showing the city before and after the flood. 247. Other Flood Problems of the United States.— There are many serious flood problems in the United States and comparatively little has yet been done toward their solution. About 1,700 square miles of the valley of the Sacramento River in California has been subject to frequent and serious overflow. This problem has been studied by various commissions in 1880, 1894, 1904 and 1910 and a considerable difference in opinion developed as to the best methods for its solution. The. question has now been settled and some work is being done along the .lines adopted by the State and Federal authorities. This problem is only second to that of the Lower Mississippi Valley. 13 The great loss in the Miami Valley due to the flood of 1913 has re- sulted in the formation of the Miami Conservancy District, and the c Flood Control, H. M. Chittenden, International Engineering Congress 1915, Waterways and Irrigation, p. 157. 558 Floods and Flood Flows. preparation of the most comprehensive plans for the flood protection of that valley that have yet been attempted in any country. 7 These works are now (1919) under construction. The rainfall which caused the great flood of March, 1913, is dis- cussed and illustrated in Sec. 129, p. 266 et seq. and the flood condi- tions at Dayton are shown in Figs. 10 and 11, p. 40. The City of Co- lumbus and other cities in the Valley of the Scioto River suffered seriously in the same flood and preliminary plans for protecting works have been made, 8 but differences in opinion as to the nature and char- acter of the work have arisen which have prevented the consummation of the plans. The City of Pittsburg has suffered seriously from the flood of the upper Ohio and its tributaries, and comprehensive studies have been made of its flood problems 9 but nothing material has yet been done toward permanent flood relief. At Kansas City the bottom lands along the Kaw River, which are the center of transportation, commercial and industrial activity, were damaged to the extent of over $30,000,000 and a loss of 19 lives in the flood of 1903. 10 While agitation for flood protection has been constantly maintained ever since that date no comprehensive plan has yet been carried into effect, largely on account of divided jurisdiction. 248. The Cause of Floods. — The causes that produce runoff and its variations have been discussed in Chapters XVI and XVII. The causes of high water, excessive runoff or floods should be evident from that discussion and may be summarized as follows : 1. Floods will occur on a given drainage area when the following conditions obtain at one and the same time, and will increase in inten- sity and duration as the conditions become more favorable to increased runoff. A. When the rainfall on the drainage area is of : a. Great intensity b. Wide distribution c. Long duration i See Report of A. E. Morgan, Chief Engineer, Miami Conservancy District, Dayton, Ohio. Also various Bulletins published by the Miami Conservancy District. s See Report on Flood Protection of Columbus, Ohio, by J. W. Alvord and C. B. Burdick, 1913. Also Report on Flood Relief for the Scioto Valley, by J. W. Alvord and C. B. Burdick, 191G. 9 See Report of Flood Commission of Pittsburg, Pa., 1911. 10 See The Floods of the Spring of 1903 in the Mississippi Watershed, Bui. M, U. S. "Weather Bureau, 1904. Cause of Floods. 559 B. When the surface of the drainage area is impervious from : a. Saturation by previous rainfall b. Frozen condition of ground c. Normal geological structures C. When retention is at a minimum on the drainage area from : a. Cool weather b. Absence of vegetation c. High humidity In addition to the above, floods sometimes result from or are aug- mented by ice and log jams and the failure of reservoir dams. 2. In the comparison of floods on different drainage areas other factors are important : Topography, geology, arrangement of tribu- taries, surface conditions, location relative to storm paths and sources of vapor, climatic conditions, temperatures, wind velocities, etc. The maximum floods on all streams are due to a storm or a series of storms that have covered the drainage areas so as to produce a syn- chronism in the discharge of the various tributaries whereby the max- imum flood accumulates at the locality under consideration. The con- ditions preceding maximum floods are more apparent from a study of the larger streams where numerous data are available. Fig. 326 shows various hydrographs of the Mississippi River at Cairo during the six maximum recorded floods that have occurred at that place. For each flood at Cairo comparative hydrographs are shown of the Upper Ohio at Cincinnati, of the Tennessee River at Chattanooga and of the Missis- sippi River at St. Louis. The elements of flow conditions at these various stations are given in Table 58. TABLE 58. Elements of Flow Conditions at and Above Cairo. Gaging StatioD River Drainage Area Above Station Sq. Miles Flood Stage Feet Height in Stage Feet Lowest Stage Feet Distance Above Cairo Miles Cincinnati, Ohio . . Ohio 72,684 21,418 699,000 203,900 50 33 30 71.1 58.6 41.4 1.9 0.0 —3.1 500 Chattanooga, Tenn. St. Louis, Mo Tennessee .... Middle Miss. . . Ohio 505 191 Cairo, 111 Mississippi . . . 712,700 45 54.8 —1.0 A Comparison of these six great floods with the normal spring flood at Cairo is shown by their hydrographs in Fig. 329, page 565. 560 Floods and Flood Flows. 1662 I I ff- Cincinnati. C- 5tl 01/ is. B- Chattanooga. D-Cairo 1837 1883 A R \ /iv r V B ^ i V " [ ^v v ^-^. c '"~ N \ D 1884- \ 1 \ \ \x l\ \ \ > A/7 i\ A ley i V \ c \ D f\. 1912 a i> ; k ' \l,\ A 8 4 \ , \ ,1' 1 ^ \ c. D \T 1913 | A 1/7 J A P ! W IS 1 4 1 i ! 1 '. / c \0 \ r\ vi C 21? 40 60 SO O 20 40 60 30 Q ZO 40 60 30 Time - Days- Fig. 32G.— Hydrographs of Mississippi River at Cairo and of Various Tribu- taries during the Six Maximum Floods at Cairo. Cause of Floods. 561 From Fig. 326 it is evident that the crests of the various floods at Cairo are due to high water in the tributaries as follows : 1882 Upper Ohio and Middle Mississippi 1883 Upper Ohio and Middle Mississippi 1884 Upper Ohio and Tennessee 1897 Upper Ohio, Middle Mississippi and Tennessee 1912 Upper Ohio, Middle Mississippi and Tennessee 1913 Upper Ohio, Middle Mississippi and Tennessee The frequent and excessive floods of the Ohio River result from the fact that the normal tracks of storms from the southwest parallel its course. (See Fig. 153, p. 274 and Fig. 321, p. 552). In all cases it is noticeable that the floods in the Upper Ohio dominate the Cairo floods and the exceptional floods are produced by a combina- tion of floods in the Upper Ohio with those from one or more of the other large tributaries. It is also evident that if a flood ever occurs that combines high water in the Mississippi River, such as occurred in 1844 at St. Louis (Fig. 326, p. 560) with high water in the Ohio such as occurred at Cincinnati in 1884, together with the high water that has occurred on the Tennessee or some of the other minor tributaries, Cairo will experience a flood of a magnitude materially greater than has as yet occurred within the period of the limited records. An interesting and instructive extension of this study can be made by adding to these diagrams hydrographs of other large tributaries to the Mississippi River or by confining the study to several of the minor tributaries and the main tributary into which they flow. 11 249. Time of Occurrence. — Any series of hydrographs showing the daily runoff from a drainage area (Fig. 284, page 488) will show periods of high flow which ordinarily occur at more or less certain dates but vary considerably in quantity, and consequently in crest height. If the series examined covers a long term of years, occasional floods will be found to have occurred at dates quite remote from the date of common occurrence. In general through the northern part of the United States normal floods occur in the spring, for while at that season normal rainfall is less in intensity, distribution and duration, than during the summer, the ground is then more impervious, evaporation is at a minimum, and ground flow from the stored water of winter is at a maximum. Never- theless observation will show that occasionally on some streams in these parts of the country even higher floods occur at other periods on account 11 Daily River Stages on the Principal Rivers of the United States, Parts I to XVI, U. S. Weather Bureau. Gives gage heights from the earliest records to and including 1917. Hydrology — 36 562 Floods and Flood Flows. ■ 5i t> iT> ^ "- 0) N ^ °) ""• ^5 K >0 "l lA fh N. 0j (^ Ifj (V) ^ (Jj (V t(\ 1 ^} \t ^ ^ \t "5 ^ "^ ^ <*> % % t\i ; w Occurrence of Floods. 563 of occasional abnormal conditions of ground saturation and rainfall. Fig. 327 shows the relative dates of occurrence and height of the max- imum annual floods on various rivers of the United States. 250. Relative Time of Occurrences of the Flood Crest in Rivers. — In a rising river the advance of the the peak of the flood wave does not in general represent the velocity of the flowing waters (Fig. 287, p. 493). When a flood advances from the head waters of a stream the advanc- ing wave must first fill up the river channel or immediate valley to the flood line, hence the peak of the wave at any point farther down the river is in general caused by water that has passed any upstream point at a time later than the occurrence of the flood crest. When the flood* is caused by rains or melting snow more or less general in extent, the flood wave may be caused by the local runoff or by combined local and headwater runoff, and the peak of the flood crest in the lower valley may occur earlier or may be simultaneous with the flood crests at points on the upper river. (Fig. 328 ). 12 The relative time of the flood crest therefore is entirely a matter of distribu- tion of the rainfall or snow that produces the flood and of the flood channel capacity. Occasionally the sudden advent of large bodies of water into a pool or river of low gradient, such as is occasioned by a sudden flood pass- ing a high dam into a pool below, will set up waves of translation which move with high velocities and much faster than the flowing water. These sometimes progress upstream in opposition to a river flow as in the case of the arrival of a tidal wave at a river mouth. Mr. Wm. J. McAlpine 13 states that a wave of translation in the Black River, occa- sioned by the failure of a dam, passed from Lyons Falls to Carthage, a distance of 40 miles, in two hours, while the flood wave did not reach Carthage until six hours after it first passed Lyons Falls. He also states that the sudden discharge of water over the dam at Lowell on the Merrimac River due to the closing of the wheels on Saturday nights, causes a rise of water fifteen minutes later at Lawrence, thir- teen miles below, although floats require twelve hours and more for their passage. Mr. J. Scott Russell 14 uses the formula given in Sec. 52, p. 92, to calculate the velocity of such waves in canals and rivers. (See also Sec. 58, p. 105.) 12 From unpublished data, Miami Conservancy District, by permission of A. E. Morgan, Chief Engineer. 13 Waves of Translation in Fresh Water, Wm. J. McAlpine, Trans. Am. Soc. C. E., Vol. 1, p. 383. 1 4 Beardsmore's Hydrology, p. 211. 564 Floods and Flood Flows. Rive ps and Creeks C/ties and Towns Fig. 328. — Time of Occurrence of the Flood Crest at Various Points on the Great Miami River during the Flood of March, 1913 (see page 563). Occurrence of Floods. 565 251. The Rise, Duration and Recession of Floods. — In the occur- rence of floods, the time which is taken for the flood wave at any point to rise to its peak, its duration at and above the flood stage, and the time required for it to recede depend particularly upon the size and shape of the drainage area, the arrangement of the tributaries, the storage, and on the distribution, duration and intensity of the rainfall pro- ducing it. The floods in large rivers usually rise slowly, endure for a January February March April May Fig. 329. — Comparative Gage Heights of the Six Maximum Floods at Cairo, 111. considerable period and slowly recede, while in small streams the rise is rapid, the duration short and the recession rapid. In the great rivers (Fig. 329), each period may be several weeks in extent. In large streams (draining several thousand square miles) the periods are com- monly several days (Fig. 330) while in small streams the periods may be only several hours in duration (Fig. 331, p. 567). When no surface or subsurface storage exists on a drainage area, and when a stream has adequate channel capacity (Fig. 184, p. 326) so that there is no overflow and consequent valley storage at flood stages, the time of flood advance and flood recession is approximately equal. In most cases some storage exists and in consequence flood advance is in general more 566 Floods and Flood Flows. rapid than flood recession. The presence of storage on a drainage area therefore reduces the intensity of the flood peak and prolongs the duration of the flow (Fig. 337, p. 575). Both the time of occurrence and the duration of floods in any stream vary greatly, however, with the intensity and distribution of the rainfall, and extraordinary floods may depart radically from the normal. (Figs. 330 and 331.) 13 -- ■-■- c: nz q i- - r \ " \i\ \ ± 33? i: nz_i_ « - - ■-- i\n& ' 2 IwrN I'll \i ■ "^~''" s - W hN -~ r ^ wci "*¥*•■ *" " v " i \ - . . iff [TO . . H--U- / '■ Ai\ M\H"- r '■ i* 92 • " '•■ W\l\ V\v- '■> ! 1 \ / r ^ ' imy\ \\\\ \ \ ■ s ■} 1 in ~ ■ ' W\ v Vl ' ' ^\ -\ / '\ 10 1- \'-JM\ . XV*'- \- S \V - >-• I - l . .. r m ■ N\n v , x\ \ \ ■•' / l90B \ c 1 X >m • ■ \) \ X ' [ /■ ■ 3 i i. .. -'/ \/4U>, - --- Li \a_i_ \ \\ ,/, , ,/, ^_ r t ■/'/- fti.l. L..4. vv V / \ ■ !vi-^ J 4 /// ///■ . V , x jt>X 1 / ~\\ IsL |i 2 ^ t J//..u\\\ ... rivv\^\ - >- ^ - \N-^rKfv.- i /' /\\ . /if . 1 1 , \\a^sS » f \ / ! Av»/ s - j /,-/ i.i_L _ / / . ././.i. V- ' W - \/ A- •-/ - ^p 9 - -1 //• \ \W ^ / /U.j: - > k- ■ Sv 3' -F^L //[,'.■ y \>\ v MM/ 1 • \ A/j> k •*• " ' :// ' f vx~X r\ // ^ // \ \ vf^t ;7 \ * -■ mir VK/\ \ jf/\r\i: \ \ \ \ \\^ ?t X ^^ &■' ///; '• j> \ ,7 / \/ /// \ i ■ v\ y- : " /// I -< \ \ V 7 / / \'J X S \ ^jE 5 ,«-,_ MA ' ' r \ a -1 ^ 4i ^* -^ ^^ v \- S3 v-3 v/ ^ C: " ' iff'Xst- ' > "- X ^ jT S - K ~ ■■- 1 M'-^ % ^«« : ^^ ■% , /ass J' / A .' ,/■ /? ,-S \ S \J. V A-. <5 ■ iBSS^l 1 : \ t. ^ . \ .'-;./. \ . / \\/i4 - 1 " ' / A 3 / T"t1; r x , '• / M. \ ' \ ' ^ ,x /; S %'t Qlif _S . rrr ^s^S ITT ( ^5 J 1 y ;V -"^ r — - < / / t \ , / T*\ J^ 5 ,^/ ... ! h ^ 1 £ y \' ^S /JBH 1 \ \ '<' '\ ^ I-- //! 1 ■ *• «' v"'-^ T §> ' H 1 !■ 1 ! v<-\'" < ^ , -^//^-'\^--. i + "- 1 I - " 1 i i .... ... 1 ■- 1 i I -I- -F + -\- +i- 77/-".? />7 Days Fig. 330. — Advance, Duration and Recession of Various Floods at Kilbourn on the Wisconsin River. The relations between the flood waves and the time and amount of the rainfalls producing them are shown for the March, 1913, floods on the Scioto and the Miami Rivers in Fig. 332. The quantity of flow and the consequent flood height affects the ele- vation to which levees and other protecting works must be built, and the duration must influence the character of construction in order to minimize seepage and prevent destruction. The occurrence and dura- tion must also modify the size of reservoirs and detention basins, and the peak flow must constitute the basis of spillway design. Rise, Duration and Recession of Floods. 567 March March 24 Z5 26 27 23 29 30 24 25 26 27 28 29 30 IVVCH? 7\ Cast Canada Creek Da/aevil/e, NY \ 2S6 Sq. Mi. B. Sattenkilt River Gr&enivich. NY / v^ J \ 444-Sq.Mi. s "> /zoooo j> 1 1 aooo K ^JOOOOO 1 0) (J $ 30000 Q 70000 C. 5chPharie Creek Fort Hunter, NY 909 Sq. Mi. a Mohawk River LittleFatls.NY 1306 Sq.Mi. V *>-«. 40000 20000 A f. Wabash River La Fayette, Jnd. 7300 5 a. Mi. rTfiua/son River Mechanics villefl. Y. 4500 Sq Mi. ^Nj \ \ / \ 1 £ ^> t \l 7 / / \ \ / \ / / \ \ w / / / > / 1 1 \ \ 1 1 1 v. / f / 1 / f 1 23 Z4 25 26 27 23 29 30 March fipril Fig. 331. — Advance, Duration and Recession of Flood Waves of March, 1913, on Various Streams. After A. H. Horton. 568 Floods and Flood Flows. The records of flood flows may give the average maximum gage height or discharge for a 24-hour period or the gage height and max- imum discharge at the time of the flood crest. The latter will exceed the former by a considerable percentage and the difference in the records should be carefully distinguished. In the flood discharge of great rivers such as the Ohio and the Upper Mississippi River the flow .5 IP, 1? 4 4s .V ■S ii a V * / fO ■4 * ^ 3 * £ d «i M: / ill Sc/ofo R/Ver abore 1 1 Co/u/nbus ,0 h/o. 1 1 Miami ff/ver 1 1 1 1 i . abose Dayfon, Ohio 1 Rer/nfa/ / -^-Ra/nfa// n Run off ^Runoff \y 1 1 — ~~l — /-)' X '// ,^, — / t - ty£ l^-" ( 1 h- 1 / f > \J I t • '<* ^ /' \ »^>> -w """- 23 24 25 26 27 28 29 30 3/ M&rch / 2 23 24 25 26 27 28 29 30 March Fig. 332. — Relations of Rainfall and Flood Waves on the Scioto and Miami Rivers for the Floods of March, 1913. and crest height for the day of maximum flood vary but little from those at the hour of maximum discharge. In small- streams, however, there is a great difference between the average discharge for the maxi- mum 24 hours and the discharge at the crest of the flood. The maxi- mum crest height and the maximum crest discharge is most important in certain engineering problems. Mr. W. E. Fuller gives the follow- ing approximate expression for the relations of maximum rate of flow to average maximum 24-hour flow. 13 Q max. = Q rhich ( 1 + 2M-0-3 ) Q m . lx = maximum flood discharge in cu. ft. per second Q = maximum average 24-hour discharge in cu. ft., sec. M = drainage area of the stream in square miles 15 Flood Flows, W. E. Fuller, Trans. Am. Soc. C. E., Vol. 77, p. 564, 1914. Flood Frequency. 569 This formula gives values for the maximum flow in terms of the average 24-hour flow as follows : Drainage Area Maximum 24-hour Maximum Flow Sq. Mi. Per Cent. Per Cent, of 24-hour flow 1. 100 300 10. 100 200 1000. 100 125 This formula, as in the case of all other formulas, must be taken as a general expression to which there are numerous exceptions. For example, the flood in Schoharie Creek in March, 1913, at Ft. Hunter, N. Y. (Fig. 331, p. 567) had a maximum flow of 141% of the maxi- mum 24-hour flow. 252. Flood Frequencies. — From the record of past floods it is evi- dent that the average flood to be expected every year is exceeded by floods of less frequency that may occur at intervals of five to ten years, and that these will be considerably exceeded by greater floods which may occur at intervals of from 50 to 100 years, and that still greater floods must be expected at longer intervals. It is to be noted that the intervals mentioned are merely averages, that there is little regularity in the occurrence of floods of great magnitude, and that such great floods may follow each other at lesser intervals but that the average appearance of the greatest floods is rare but uncertain,. The highest flood on record at Cincinnati, Ohio, to that date was the flood of 1882. This flood was exceeded by the flood of 1883 which in turn was again exceeded by the flood of 1884 which has not been equalled since that date. In the 103 years of record on the Rhine 10 (Fig. 333) there has been one flood above 25 feet, seven floods above 24 feet, eleven floods above 23 feet, twenty-eight floods above 22 feet, and fifty-nine floods above 21 feet. On the Seine River at Paris no flood 'equal to the flood of 1615 has occurred since that date (Fig. 334) 1T The two floods next in magni- tude occurred in 1658 and 1910 respectively, while six floods above 25 feet and fifteen above 20 feet have occurred since 1600. The great flood of 191 3 on the Miami River was preceded by a flood 10 From Decrease of Water in Springs, Creeks and Rivers, Gustave Wex, Washington D. C, 1880. i" Gage Heights on the Seine River at Paris from paper of M. Belgrand An- nals du Ponts et Chaussees, 1852, premier semestre, p. 102. Also Report on the Influence of Forests on Climate and on Floods, W. L. Moore, p. 18, and Eng. News, Vol. 63, p. 327, 1910. 570 Floods and Flood Flows. almost as great in 1805 while other great floods of lesser magnitude occurred in 1866, 1883 and 1898. At Cairo, Illinois, located at the junction of the Ohio and Mississippi River (Fig. 319) there have been since 1868 six floods above 52.5 feet, (Fig. 326 and 329) ten floods above 50 feet and thirty-two floods above 45 feet or the bank full stage (Fig. 320). 7770 1780 J 790 /80O /8/0 /8B0 /830 J840 1850 /860 /870 Fig. 333. — Maximum Annual Gage Heights on the Rhine River at Emmerich, Germany. After Wex. Where records of considerable periods are available the frequency of floods may be considered mathematically, as was the extreme rain- fall records in Section no to 112 inclusive but such calculations must not be taken too seriously. 'Mr. L. F. Harza, Engineer of the proposed 1600 /650 /700 /750 /800 /850 /QOO 29 28 27 \26 l5 25 » 23 \ 22 %20 & /9 ,ts /8 b ,7 /6 Fig. -Gage Heights of Maximum Floods on the Seine River at Paris, France. power development at The Dalles on the Columbia River 18 considered the flood flows of the river at the proposed power site by probabilities (Fig. 335) and the results would indicate that the great flood of 1893 is Report on Columbia River Power Project near The Dalles, Oregon, L. F. Harza, Project Engineer. Technical Pub. Co., San Francisco, 1914. Forests and Floods: Extracts from an Austrian Report on Floods of the Danube, H. M. Chittenden, Eng. News, Vol. 60, p. 467, 190S. Flood Frequency. 571 would not be exceeded more than once in 1,000 years. This flood has actually occurred once in the 60 years of record, hence the only safe conclusion is that such a flood need not be expected at frequent intervals although even a greater one may occur in any year. 253. Are Floods Increasing in Intensity and Duration? — Much of the United States has been settled less than a century and in many 7300 /EOO //oo fyooo 90O ^800 ft) (£ 700 .0 ^ 60O ^400 1 § 300 % § &0 t too c /894 /v 'ood. Tc^o 'oN t ^;:o< ^ X^)] tf^ t N ao/ 0/ Fk;. 335.- / 99 5 W £0 30 40 50 60 70 80 90 95 F-'erceni-crqe of frequency Probabilities of Flood Flows on the Columbia River. L. F. Harza. 99.9 99.99 After cases the maximum flood that must occasionally be expected has not occurred since the present communities have become important. In other cases serious losses of life and property have occurred and as the years pass and importance of the communities increases, more serious losses are to be expected. The occasional great flood which only rarely swept over the level area of the flood plain did no noticeable damage until man attempted to appropriate these areas for his own use, and hence the occurrence of these floods passed almost unnoticed and un- recorded. When, however, these occasional exceptional floods occur on thickly settled flood plains the loss becomes great and unprecedented. On account of these losses and the fact that they have never been experienced previously in the affected region claims are made that 572 Floods and Flood Flows. floods are increasing in frequency and in height or volume due to the changes wrought by man in the settlement of the country. The foresters and others interested in reforestation have endeavored to show that deforestation has resulted in increased floods and reduced low water conditions. Engineers in general, however, are of the opinion that deforestation and cultivation have produced no radical changes of the kind indicated. In general it may be stated that the time of observation in the country has been too brief to determine in an entirely satisfactory manner whether or not there has been any considerable change in flood height. The information available indicates no great changes except those due to channel restrictions. In the case of the longest records available the information is not wholly reliable for, while the gage readings are continuous, it is apparent that the datum or zero of the gage may have been sometimes altered either by accident or design. The high flood of 1805 preceding the great flood of 191 3 in the Miami Valley, and the records of the floods of the Rhine at Emmerich and especially the records of floods in the Seine at Paris all serve to indicate the occur- rence of great floods but show no evidence of any material change in flood heights. In many cases flood heights have increased due to the restriction of the channel by levees built to prevent overflow or by encroachments due to the filling in of low lands for building sites. The general flood heights on the lower Mississippi River have been raised in this manner by the construction of the extensive levee 'system along that river. The flood elevation at Memphis, Tennessee, has been thus increased by eight or ten feet. Fig. 336 shows the maximum high waters on various rivers of the United States. For the earlier years only maximum floods are shown, authentic records of which were preserved on account of their unusual character. For the later years annual high water elevations are available. These records show no radical changes in flood heights but indicate that occasional floods which greatly exceed the ordinary annual high water flow must be expected. Such extreme floods apparently occur once in fifty or one hundred years, although there is no reason to believe that they may not follow each other at much shorter periods. On the other hand, the longer experience on European rivers seems to indicate that periods of several years of ex- cessive floods or of unusual low water frequently occur. Probably the most conclusive evidence that there has been no material changes in extreme flood conditions is furnished bv the investigation of Flood Intensity and Duration. 573 ^o 'O o 30 eo JO o 40 30 eo /o • o 1 i 1 1 1 Con at t necticut River 'prinafiela'. Mass. i_ iiiiiiiiiiiiiliiiii! ■■■t i Ohio R 1 iver ■ a t Pit 1 tsburq .Pa. i ll 1 I 1 ijl lillll 1 [mhltinhll illlll III ill 1 < i I II 1 1 1 1| III Mississippi Rive at 5 t Louis .Mo. l ll 1 1 li III 1 ijl ll Oil ii llii lUliii b Jtudii" iHIiilIt fiJtl ■ 1 If ll ill 1IIM Mississippi /? at Memphis, T >rer | | iiii ii III III 111 llllilll |H illlllllllllllllllllll mini ll i Missc 7f Ka, isas Rii/er 0. i 1 ii liillill lull Hill Hi III Ml llflffilllUIIIIIDIIKU Cotu at The rnbia Dai/ei Rwer -.Ore. ill 1 1 1 1 111 III 111 ill lull III III Hi ll ll llllilll IIIODIIDIlllllllllllllill to po .to ID WO ft to- O SO eo to o 50 ■no 30 eo to 1780 /T90 1800 18/0 /SeO /830 /840 18S0 /860 t870 t880 /890 /900 J9I0 1920 Fig. 336. — Maximum Annual Gage Heights on Various Rivers of the United States. 574 Floods and Flood Flows. M. Ernst Landa, Chief of the Hydrographic Bureau of the Austrian Government, in his investigations of the floods of the Danube, 10 with special reference to the floods of 1897 and 1899. M. Landa reviews the records of the excessive floods of the years 1012, 11 18, 1126, 1193, 1194, 1195, 1210, 1234, 1235, 1236, 1275, 1280, 1281, 1284, 1285, 1295, I3 12 - I3I5' 1316, 1317, 1340, 1342, i359> 1402, 1404, 1405. 1406, 1407, 1408, 1409, 1434, 1437, 1445, 1464, 1465, 1491, 1499, 1501, 1508, 1520, 1527, etc. The floods of later years while described in greater de- tail in the original report are not mentioned in detail in the translation. Mr. Landa's conclusions are as follows : "To conclude from this chronological record of the Danube floods that these catastrophes have increased in number, extent and frequency in modern times would be as absurd as to maintain the opposite. The history of the past tells of floods which were not subordinate to those of the present in any of the above particulars. Two conclusions clearly follow from this retrospect : "(a) The floods of 1897 and 1899 were not abnormal or unusual phenomena in the history of the river. "(b) Regulation works have had absolutely no influence in increas- ing the heights of floods." General Chittenden in commenting on this report says : "The number of floods cited by the author is about 125. Many of them were accompanied by ice gorges which render close comparison with other floods by means of discharge or gage data rather uncertain. A noteworthy feature of the record is the occurrence of flood years in groups. In nearly the entire period, high flood years were bunched together, showing that precipitation moves in cycles." 19 254. The Effect of Storage on Flood Heights. — It has previously been noted that the effect of ground or surface storage is to reduce materially the flood heights (Sec. 203, p. 456), and that high floods may be entirely obviated by artificial control (Fig. 274, p. 464) where such control is physically possible and financially practicable. From this consideration it becomes evident that the relative floods on even ad- jacent streams may vary greatly with the natural storage on their drainage areas. Mr. W. E. Fuller has considered the effects of stor- age on flood conditions under certain assumed conditions which though necessarily hypothetical are instructive (Fig. 337). Even where little natural storage may exist in the ground or in lakes and swamps, the n» Forests and floods, Extracts from an Austrian Report on Floods on the Danube, H. M. Chittenden, Eng. News, Vol. 60, p. 4G7, 1908. Effect of Storage. 575 temporary storage produced by the overflow of river valleys during floods will modify to a considerable extent the flood heights and dis- charge at points farther down the stream. In many alluvial valleys the normal heights of extreme floods cause an extensive overflow by which large quantities of water are temporarily impounded in the bottom lands until the receding floods allow them to drain back into the streams. The amount of such storage in the lower Mississippi valley prior to the construction of the levee system was enormous (see Sec. 245). ^700 ^600 ff V vith no 3 tore ge if/ V / / t V / $ / w /« *> ^ 1/ 81^- /2 ie 20 Time of Flood tn fiours. 24 28 32 Pig. 337.— Effect of Storage on Flood Height. After W. E. Fuller. The flood plain of the lower Mississippi River has been built up by the deposition of sediment adjacent to the river channel and the bottom lands slope back from the channel to a considerably lower elevation than the river bank and are drained by various tributaries which enter the main river many miles below. The section of the valley from Memphis westward to Crowley's Ridge is shown in Fig. 338, from which it will be noted that the floods prior to the construction of the levees could overflow a section about 37 miles in width. By the construction of levees the floods are now retained in the river channel and the conse- quent flood heights at Memphis have been increased eight or ten feet above the elevation to which they rose in times prior to the construction of these levees, as will be noted by reference to Fig. 336. When channel improvements are undertaken to reduce or prevent overflow in a river valley, the storage which has been hitherto effective in reducing flood heights at such times is removed or reduced and higher floods will consequently be experienced at points farther down the 576 Floods and Flood Flows. stream. This is an important matter which is frequently neglected in plans for levees and channel improvements. In considering plans for the flood protection of the Miami valley, a study* was undertaken to determine the maximum discharge that would have occurred at Dayton and Hamilton in the 1913 flood if the river channel had been improved to a capacity sufficient to permit the water to flow directly down the channel without overflowing the flood plain. The total quantity of water stored above Hamilton at the time of the peak of the flood was 568,000 acre feet or about .3 of the total rainfall which produced the flood, and equivalent to a depth of 2.9 inches over the entire drainage area. ^< **- U- to 5* ' §22P 0: \ 'Mt 1.217-8} 1 1 .<0 * a <-- -§zpo 1 s~\ § 5j 40 35 30 25 20 1 5 I P 5 9 Miles Fig. 338.— Profile of the Alluvial Flood Plain of the Mississippi River from Memphis, Tenn., to Crowley's Ridge, Ark., along the C. R. I. & P. Ry. After Mississippi River Commission. With the channels enlarged to confine the entire flood flow to the river channel, no storage on the flood plain would obt-ain but the channel storage would be increased due to the necessary increase in their capa- city ; hence the net amount of storage elimination would be the differ- ence between the valley storage which could practically be eliminated, and the increased channel storage. The valley storage extended far up the tributaries and not all of it would be affected by improvements of the main river channel, although the depression of the flood plain in the main channel would draw down the flood plain of the tributaries to a considerable extent. In this study the assumption was made after *This example (see Fig. 339, page 578), is taken from an unpublished study of the effects of eliminating storage in the Miami Valley by Assistant Engi- neer, K. B. Bragg and is here published by permission of Mr. A. B. Morgan. Chief Engineer. Effect of Storage. 577 due consideration, that the reduction in valley storage would equal 451,000 acre feet or about 80% of the total valley storage. The excess channel storage which would be created by the necessary channel im- provements was estimated at 194,000 acre feet. This amount deduced from the 451,000 acre feet assumed to be eliminated from the overflow of the valley would leave a net reduction to be removed by the channel of 257,000 acre feet. The Miami River began to overflow and the valley storage above Hamilton became appreciable when the flow at Hamilton reached a discharge of about 40,000 second feet, and reached its maximum about 34 hours thereafter. As all of the valley storage was empounded with- in this time, that part of it which would be eliminated would necessarily have to pass Hamilton by the time the flood peak occurred. To de- termine, therefore, the resulting maximum flow of water which would occur at Hamilton, provided valley storage were eliminated, this addi- tional quantity of water must be added to the Hamilton hydrograph between the hours when the overflow began and the time at which the flood peak occurred. As the flood actually occurred, this valley stor- age which would be eliminated by channel improvements was stored above Hamilton at the time of the peak and passed through with the recession of the flood wave. If the storage were eliminated this amount of water would be added to the advancing flood wave or to the front part of the hydrograph and would be withdrawn from the receding wave or be subtracted from the latter part of the hydrograph between the discharge limits of the maximum and the time that the falling flood had again reached a discharge of 40,000 second feet, thus keeping the total flow between the overflow limits the same. This calculation can be made most accurately by graphical methods. The general shape of the revised hydrograph was determined from a knowledge of the char- acteristics of inflow and outflow curves from retarding basins, and the exact dimensions were determined by planimeter by making the additions to and the deductions from the hydrograph equal to each other and to the amount of storage eliminated (Fig. 339 A). From the investigation the maximum flow at Hamilton under the improved channel conditions was found to be 500,000 second feet or about 150,000 second feet above the flow that actually occurred. A similar study was also made of the increased flow at Dayton by the elimination of the valley storage above that city which showed an increased flow at that place of about 80,000 second feet (Fig. 339 B). Hydrology — 3 7 578 Floods and Flood Flows. Si" r ^ 1- -1 , ■ -1- J i;.. - 5J r ^ ^ £ - 1? ft s 4 • T 5 to 1 ^ :! 01 <5i > . ■5 > F r •a N^ ■a "J l> o> ^ > ^ a ^ ^ -o M ^ l 3 o is r* -V, O 1^ ^ ■j3 M ^ is 0>" £* MJ ^ c IVl c> 4-3 !? J.S o> :-r TJ s3 "1 Hi 03 O „ VI m 0> C. X2 3] i^J o> o u s 15 ^ va > N Ci Cb «i Ci ^ Q> ^ <>0 v£> \)- C\i ") ,N IM N N N e> Runoff Formulas. 583 great number of conditions that modify the results. For this reason most of such formulas are of little use except for the purpose of rough approximation. Fig. 341 shows graphically the formulas of Kuichling 20 for flood flows under conditions comparable to those in the Mohawk Valley, New York, and indicate the data upon which such formulas are based. $400 % \ \300 1 &/O0 • c e.nc fes f/oods of O/7/0 -/9/S. ' Observations - f*7/am/ ffiver and Tr/butar/es ® A Sc/ofo « , Upper and Louver. © O/enf 'angry •■ .© \ QFrom ffepart et \f)/vord and Burdick to frank /in County •\ ** • ' . • ^s "r?" '_ B n f u "~- W 7 7$ - c"- t e A/o.2 t ( 9* Curve Aio./V 1 1 1 /OOO 2000 .3000 Drainage flrea /r> Square fti/es f/oods /£} vYisconsin. X Denotes Observations- - B/ack B/ver v'a/Zey. o - Wisconsin ■■ A •■ •■ Chippewa • ■■ ® © from Paper by C B. Stewart - Western — Society of Engineers -Vo/. /SB 29 O with Additions. •StjeMyart^Curye r/*7err/// and '£•841 above.) £'80- /OOO 2000 3000 4000 5000 6000 7000 8000 9000 / 00.00 //OOO Dra/nage fire a - Square M//es = A7 Fig. 342. — Various Conditions to which Kuichling's Curves do not apply. A study of the data platted on this diagram and used as a basis for these formulas shows that they consist of most of the records of maxi- mum runoff of the streams of the world that were available at the time the formulas were devised, and that the conditions of runoff of many of these streams are in no sense fairly comparable with those conditions in the Mohawk Valley. It would therefore seem that the formulas were not intended to be limited to the Mohawk Valley but were for general application, and for such purposes they, together with other similar formulas, have come to be more or less commonly -o Report on New York Barge Canal, 1901. 584 Floods and Flood Flows. employed. That a general use of such formulas is entirely unwarranted will be seen from the following illustration of their applicability to two areas in northern United States where conditions might easily be sup- posed to be somewhat similar to those in the Mohawk Valley, much more nearly comparable than many of the areas from which runoff data were actually used as the bases of these formulas. Fig. 342 A is a comparison of the flood flows of 1913 on the Miami and Scioto Rivers and their tributaries with Kuichling's curves and shows that if flood protection works on those rivers had been based upon the formula for "rare floods" they would have been entirely in- adequate. Fig. 342 B is a comparison of the maximum flood flows on certain Wisconsin Rivers which shows that even Kuichling's formula for "occasional floods" would probably give results too large and re- quire works too expensive for that stream. This diagram ?lso shows a discharge curve recommended by Mr. C. B. Stewart for application to the Wisconsin River at and above Merrill, Wisconsin. It may be remarked that even within the State of Wisconsin the maximum floods so far experienced differ greatly on different streams. The maximum floods on the Wisconsin River are about double those on the Rock and Fox Rivers while those on the Black River are about fifty per cent, greater than those on the Wisconsin. It therefore seems evident that no general solution of the flood problem is possible but that each problem should be considered in detail and should be based on data that are truly comparable.* 256. Runoff From City Areas. — In calculating the runoff from city areas somewhat different forms of expressions which are also applicable to the runoff of streams are used. In these formulas (Table 60) the rate of rainfall (see. Sees. 124-128) and the slope of *For records of flood flows see: Report on the Barge Canal, State of New York, 1901, p. 844 Hydrology of the State of New York, New York State Museum Bui. 85, 1905. Geological Survey of New Jersey, Vol. Ill, "Water Supplies, 1904. Reports of Floods, U. S. Geological Survey, Water Supply Papers 88, 92, 96, 147, 162 and 334. Reports on Surface Water Supplies of the United States, U. S. G. S. Water Supply Papers. Reports of Pennsylvania Water Supply Commission. Reports of New York Water Supply Commission. Reports of Maine Water Storage Commission. Flood Flows, W. E. Fuller, Trans. Am. Soc. C. B., Vol. 77, 1914, Tables 12 to 27 and Table 37 in discussion of this paper by Mr. Kuichling. River Stages, Vols. 1 to 15, U. S. Weather Bureau. Runoff From City Areas. 585 the drainage area are considered as factors, and certain coefficients are introduced which should be modified by the local conditions of sur- face, storage, topography, etc. The determination of the coefficient for local use requires a study of the results which have obtained in other places where similar conditions have prevailed and a comparison of such conditions with those of the locality for which similar or modi- fied results are desired. For the conservative application of these formulas to local problems the engineer should refer to their more extended discussion in the references given. 257. Flood Runoff From Drainage Districts. — The flood runoff from the low flat lands of drainage districts is from the nature of the area drained much less intense than from the normal drainage areas of streams. The drainage investigations of the U. S. Department of Agriculture furnish much pertinent data concerning actual runoff observations in different parts of the country.' 21 In drainage work it is generally recognized that the amount of water to be removed from a district will increase with the amount and intensity of the rainfall, and few attempts have been made to devise formulas of general application. In each case it is usual to select or devise a formula that fits the con- ditions. (Table 61.) In the Mississippi Valley the annual rainfall and in general the in- tensity of rain storms increase from the source to the mouth of the river, and the runoff of drainage districts will likewise increase. Mr. C. G. Elliot 22; has suggested a formula, No. 1, Table 61, for calculating runoff to be provided for drainage ditches in swamps and other wet lands of the Upper Mississippi Valley where the soils are absorptive and easily drained. Such a formula should not be used however ex- cept for rough approximations until it is checked for local conditions. As the rainfall increases the discharge will increase, so in the swamp land of Missouri and the Lower Mississippi Valley higher estimates of runoff are found necessary for satisfactory drainage work. In the preliminary work of the Drainage Investigations in Northeast- ern Arkansas,'- 3 the discharge from the low flat alluvial lands were 2i See Publications of Office of Experimental Station "Drainage Investiga- tions," U. S. Department of Agriculture. 2- Engineering for Land Drainage, C. G. Elliot, John Wiley & Sons, New York, 1912. 23 A Preliminary Report on the St. Francis Valley Drainage Project in Northeastern Arkansas, A. E. Morgan, Circular 86, Office Experimental Sta- tion, p. 20, 1919. 586 Floods and Flood Flows. 13 ^ 02 o a ^_ _o _ a ^ ■d .S s o s -* i73 u 02 d a 2 £ « d 02 d 03 0) +■> d o 02 Si o > ,Q 0) o <& cS 01 d 02 d 02 u q-l ri 3 i? a-| fa 03 II *h d oO ^ II of* 1 •T, 02 tO !» ,S 02 0> a} ^ ft £ o d 02 02 02 d '3 rt CD > o O + B U) o efl f-H "3 + © CSS ^> C Ol © © CO o o t- © O rH 00 o 3 c3 O u | -' d . 02 Si OO t- fa dd w o o C- t-; r-j O © >>© 02 > oo © © 00 11 —I -I :§3 O' a 3 £ =w 02 d f- 1 a ca +■> . • £P . fe 02 '—• Cfi 5 O oo 3 fa d -. . 02 CD "3 <3 ■ *0 02 rj H ci O o ,a ft -u S-. C R-2 © .-, © w Oriri OO II II o 02 Q2 S-. a £ o 0> f^OO d oo OcnOf d °° d. S d 02 «M g 02 ft a ^ d Pi P -o d "S ,s » § «■ cS - 02 "" ® » d «< •< s w . d « .a W) d 5* o 02 & ■ 'o 5 p o o O O 6 a° = o O ^~ O II II o _ o O cm 1-1 O ft s ._! e o ■ca CN1 CO o "3 T3 ° s CO £ > a> m sl°; H H ffi.'S d fc 3 03 £ o t- 1 ai © Oh to 03 pj ft o < m Pi a a u K5 EH O CJ5 1—1 b£ g LO ^ Tt< CO u ft '3 O CO d OS P <1 d CN1 H 5 ft -5 K „ S3 >> >. - 03 TJ d 03 03 1 03 & 3 oT 0) aj S-i M '« OS a CJ ca 3 a o 0) d 3 . COCO b/ C3 M 1-1* 03 CJ d o > £ 0) 5 g CO T3 cj *-J Pi 03 CO o "3 ■+-i O CD tti CJD O pi CS 03 c3 03 pi Q3 03 02 02 PI PI s o CC] CS rQ 3 Pi "3 "3 C ^ a '5 a 3 3 03 a; «!« rt fdH l-H N CO ^' o 588 Floods and Flood Flows. calculated from Formula No. 2, Table 61. For other conditions in the same district this formula would not give adequate results. "For the more rolling and less sandy land in the east part of Missis- sippi County the estimated runoff was increased 50 per cent. For the clay soils east of Crowleys Ridge the quantities obtained by the use of the formula were doubled in making estimates, and for the slopes of TABLE 61. Runoff from Swamps and Wet Lands. Author Formula Application 1. C. G. Elliot 20 Upper Mississippi Valleya? absorp- q = \- 3.63 tive and easily drained soils VM 2. 0. G. Elliot 24 Northwestern Arkansas^ q = ^+6 VM 3. Morgan Engineer- 28.0 Mississippi County, Ark. ing Co q == \- 7.2 VM 4. Morgan Eng. Co. . . 38.0 Cache River Drainage District q = -— + 8.0 VM 5. S. H. McCrory and 35 Cypress Creek Drainage District, others q = Arkansas. 24 6 vm: 6. 90 Tentative formula for certain q = f- 10 Louisiana districts. (No consid- yj^ erable storage in bayous and ditches) 7. 3400 Tentative formula for certain dis- q== |- 5 tricts in Florida Everglades M + 50 q =1 sec. ft. per sq. mi., M = area in sq. mi. Crowleys Ridge three times the quantities determined by the formula were taken as the probable flood runoff."' 3 It should also be noted that in the actual development of some of these swamp lands it was found that Equation No. 2 would not give sufficiently high unit discharge for satisfactory drainage and formulas Nos. 3 and 4, Table 61, were the basis used by the Morgan Engineering Company of Memphis, Tennessee, in their design of the necessary works. In the report upon the Cypress Creek Drainage District in Desha and Chicot Counties, Arkansas, 24 Formula No. 5, Table 61 was used which gives materially higher unit runoff for that district ; and in Louisiana, -4 Bulletin 198, Professional Papers U. S. Dept. of Agriculture, 1915. Runoff from Drainage Districts. 589 where still more extreme rainfall conditions are encountered, the run- off must be estimated on a still higher basis and Formula No. 6, Table 61, was used as a tentative basis for the investigation of certain districts in this area. Most of the Louisiana districts require the in- stallation of pumping plants, and in many cases more or less extensive bayous are included within the levied areas. These bayous in connec- tion with the ditch system often afford extensive storage which when properly utilized reduces the size of the pumping plants which need to be installed to keep the land free from water. In certain investigations in the Florida Everglades, where rainfalls are still more intense than in Louisiana, Formula No. 7 of Table 61, was tentatively adopted as a basis for drainage estimates. The conclusions to be drawn from an examination of these formulas are that such expressions must be chosen or devised for each particular district and then represent only their author's conclusions based on more or less pertinent data concerning local conditions and local runoff. In designing ditches even in the same drainage district or in districts closely adjoining, it is not always safe to use the same expression for runoff as an area with clay soil will discharge much more water than a district with sandy soil, and a different basis must therefore be used for the design of the ditches when the condition of soil so requires. 258. Flood Flows of Small Streams for Determining the Capaci- ties of Railway Culverts. — There are comparatively few records of the flood flows from small areas the drainage from which must be provided for by railway culverts, yet these flows must be anticipated in the construction of numerous structures in railway lines. The run- off formulas used by a few railroads in determining the area of water- ways, together with statements of the confidence placed in the com- puted results, are given in the following extracts from the committee report on "Roadway," published in the American Railway Engineering and Maintenance of Way Association, Vol. 10, Part 2, 1909, to which the engineer should refer for a more extended discussion. The Pittsburg and Lake Erie Railroad (J. A. Atwood, Chief En- gineer) uses Burkli-Ziegler and McMath formulas, obtaining the area by survey or from government topographic sheets. Maximum rain- fall at 3 inches and C = 0.3. The Burkli-Ziegler formula is used only when -_ exceeds unity. A. The Chicago, Rock Island and Pacific Railroad (John C. Beye, locat- ing engineer) determines the area, slope and surface conditions of basin 590 Floods and Flood Flows. by actual survey where practicable, otherwise by maps. The formula used in Talbot's x = CtfU x = area of waterway opening in square feet. For flat area C = V 3 For hilly area C = 2 / 3 For mountainous area C =1 or more The culvert is made 50 to 100 per cent, larger than the formula calls for, when possible. The Chicago, Burlington and Quincy Railroad (T. E. Calvert, Chief Engineer) obtains drainage areas by actual survey or from reliable maps. For areas less than 1000 acres, the McMath formula is used : Q = 2.0625 V 15 A 4 For areas greater than 1000 acres 3000 M Q = — 3 + 2 V M The results are relied upon unless recorded high water marks indi- cate an extra large waterway is necessary. The Missouri Pacific Railway (W. C. Curd, Chief Engineer) de- termines areas and surface conditions by survey or from reliable maps. No one formula is relied upon but the conclusions are checked up in all possible ways. The Talbot, McMath or Burkli-Ziegler formula may receive the greatest confidence in determining the runoff, depend- ing upon the data. Some excess is always provided, depending upon the size and local conditions. The Missouri, Kansas and Texas Railway (S. B. Fisher, Chief En- gineer) uses Talbot's formula with the value of C as follows : Steep slopes C = 1.1 Medium slopes C = 0.85 Flat slopes C = 0.60 The areas and design are changed as appears to be made necessary by local conditions. The Baltimore and Ohio Railway (J. B. Jenkins, Assistant Engineer) obtains traces of former floods, fall and cross section of stream by sur- vey. This result is compared with Talbot's formula with a factor (C) of 4 or 5 for mountainous, % for hilly, y 2 for medium, %'for rolling and % for flat ground, the factor being increased in regions of heavy rainfall for shape of basin favorable to rapid runoff, etc. The opening is usually made 20% greater than would be required by the greatest known flood except when the flood was very exceptional. Formulas for Flood Flows. 591 Practically all the railroads depend somewhat upon the results of computations from some one or more of the many formulas for runoff, but in practically no cases are these accepted as a final estimate. Con- sideration is properly given to the many factors which influence the runoff but which make the preparation of any formula extremely com- plicated if not impossible. 259. The Derivation or Selection of Formulas for Flood Flows. — From the previous discussion it should be evident that runoff formulas should never be used until their applicability to the conditions of the problem is determined from authentic data derived from areas having similar characteristics and after the most complete practicable investi- gation. The formula should then be selected or derived to fit the data and conditions with perhaps a reasonable factor of safety. The use of such formulas therefore is mainly to adjust conditions or to pro- portion works designed to conserve or control flood flows from an area different in extent but similar in character to those on which the form- ula is based. For example, formula 2 in Section 257 was determined from the assumption that for an area of 9 square miles the flood discharge would equal 40 second feet per square mile and that for an area of 100 square miles the flood discharge would equal 19 second feet per square mile. Substituting these expressions in the general formula (Type 1) the value of x and y can be determined and the corresponding discharge for areas of other sizes calculated. If the resulting equation when platted does not fit the general condition, a formula of different form may be derived from other general equations such as Type 2 or Type 3. x Type 1 q = — — + y V M x Type 2 q = \- z M + y x Type 3 q = y V M The student will find it instructive to practice devising such for- mulas. For example, a formula of Type 1 may be derived to fit the conditions : Area Discharge Square Miles Second Feet per Square Mile 200 12 50 17 592 Floods and Flood Flows. and a formula of Type 2 may be derived to exceed the records of the flood flow of the Black River (Fig. 340) by 10% or 25%. Such practice will be useful in showing the method of derivation of such expressions and in giving a better idea of their true value and of the danger in their careless selection and use. 260. The Economics of Flood Protection Work. — In general the maximum flood which may be expected from a given drainage area is indeterminate. There are no floods of record so great that it is reason- able to conclude that there can be no greater. It is always possible that a rainfall of greater intensity, wider distribution and longer dura- tion may sometime occur or that other conditions may prevail which may create more serious flood conditions than have yet occurred. On the other hand, from the data previously considered there is evidence that the combination of conditions which produces maximum floods is very rare, perhaps once in 500 to 1000 years ; that floods of a lower magnitude will occur once in 100 to 200 years ; and that lesser floods of various degrees will appear in various shorter periods, not with any regularity in occurrence but as an average of past conditions. If the engineer attempts to design flood protection works for the greatest flood he can imagine, most of such works will be entirely impracticable. In the consideration of floods and works necessary to mitigate or prevent their undesirable consequences, the engineer must constantly keep in mind economic conditions. It is apparent that no works of any kind are warranted unless the resulting betterments exceed in value the cost of the improvements, and the parties interested are able to raise the funds necessary to meet the expense which will be incurred. Where such works are undertaken by a community the law requires that the benefits which will be derived therefrom must exceed their costs and that the cost must not be excessive. In the construction of agricultural drainage works it is often in- expedient to provide for the maximum flood that may occur even every five years. The effect of the temporary flooding of agricultural land if for brief periods only is not serious. The interest and maintenance costs on works of a capacity suitable for extreme conditions would make their construction impracticable and it is better to face occasional losses or damages of crops than to attempt such expenditures. For ex- ample, Formula 3, Table 61, was used by the Morgan Engineering Com- pany for drainage work in Mississippi County, Arkansas, as the best which the conditions warranted at the time of construction. As was expected, the lower lands are flooded to some extent about once in three Economics of Flood Protection. 593 years and undoubtedly as the lands increase in value the ditches will be enlarged so that they will overflow only at rare intervals, corre- sponding more nearly with the conditions expressed by Formula 4 of Table 61. It should be noted in this connection that the damage caused by the overflow of levees is much greater than if no levees were in exist- ence, and that in most cases economic levee construction should be based upon a considerably higher rate of runoff than need be used as a basis of canal or ditch design. The probable damages which will be entailed in consequence of flooding due to extraordinary storms must be kept in mind in all such cases but the physical and financial condi- tions of each project will usually establish the limits of expenditures beyond which it is impracticable to go. In most cases of storm water sewer design the size of the sewers can rarely be made adequate to provide for the maximum storm which may possibly occur, and a balance must be fixed between the cost of the works required to protect the district against floods of a certain magni- tude and the damages which may result from storms of greater mag- nitude. Commonly the flood which will probably occur once in ten, fifteen, twenty-five or fifty years is used as a basis of design according to the importance of the interests involved and the comparative costs of construction. It may be shown in many cases that the extra cost of more extensive work if set aside at interest would accumulate a sinking fund in excess of the damage which would be entailed by the exceptional flood in which case extra investments are unwarranted. In the recent construction of a small water power dam in Central Wisconsin it was thought desirable to about double the spillway capa- city which had been available and sufficient in case of the old dam which had stood for perhaps forty years. It was recognized, however, that even the increased capacity of the new dam would be insufficient to pass floods which would be occasioned by storms of the intensity of that of July 24, 1912 (Table 27, page 248) at Merrill, Wisconsin, or that of June 10, 1905, at Bonaparte in Southeastern Iowa (see Table 27). In view of the remote possibilities of the occurrence of such storms it was necessary to take the chances of such an occurrence for otherwise the project would have to have been definitely abandoned on account of the great expense involved. In more important works where life may be sacrificed by failure and where great financial interests are involved, greater factors of safety must be used. In the design of the works of the Miami Conservancy Hydrology — 38 594 Floods and Flood Flows. District provisions have been made to protect the District against a flood about 40% in excess of the flood of March, 191 3 (Fig. 343 A), which is believed to be the maximum flood which can reasonably be expected, and the works under construction are designed to sustain without injury even a greater flood. 5 v. to \ 1 V \ r , \ \ \ K J 1 I / \ \ / \ — \ \ ^ , ' ^ / 1 \ \ ttsrimarea max. r/ooa 1, 8.3 in 3 Da qs. r> f I J 1 7 /0/.? Flnn/J / l 5" / f x: \ \ \ \ f •» ' S \ ^ f s h k -. 'I _ ^_ /s / 6 O I 2 3 4 5 6 Days ff- Miaimi River af Dayfon, (Phio. B - Scioto River af Co/umbus, Ohio. Drainage Area 25 Z 5 5a Mi Drainage Area I6l45a-Mi. Fig. 343. — Comparison of Actual Floods of March, 1913, with ideal Maximums for which Flood Protection Works are to be designed. 7 ' s The proposed works for the flood protection of Columbus, Ohio, also provide for a flood of considerably greater magnitude than the maxi- mum recorded flood which has occurred at the place (Fig. 343 B). LITERATURE Yield of the Sudbury River Watershed in the Freshet of February 10-13, 1SS6, Desmond Fitzgerald, Trans. Am. Soc. C. E., Vol. 25, p. 253, 1886. The Flood in the Chemung River, Report State Engineer, N. Y., 1894, p. 387. The Floods of February 6, 1S96, Geol. Survey of N. J., 1896, p. 257. Floods of the Mississippi River, Park Morrill, Bui. E, U, S. Dept. of Agric, 1897. Report on the Mississippi River Floods, Report No. 1433 U. S. Senate, 55th Congress, 3d Session. The Floods of the Mississippi River, Wm. Starling, Eng. News, Vol. 37, p. 242, Apr. 22, 1897. The Mississippi Flood of 1807, Wm. Starling, Eng. News, Vol. 38, p. 2, July 1, 1897. Study of the Southern River Floods of May and June, 1901, Eng. News, Vol. 48, p. 102, Aug. 7, 1902. The Passaic Flood of 1902, G. B. Holister, and M. ©. Leighton, Water Supply and Irrigation Paper No. 88, TJ. S. G. S. Literature. 595 The Passaic Flood of 1903, M. O. Leighton, Water Supply and Irrigation Paper No. 92, U. S. G. S. Destructive Floods in the United States in 1903, E. C. Murphy, Water Supply and Irrigation Paper No. 96, U. S. G. S. The Floods in the Spring of 1903 in the Mississippi Watershed, H. C. Frank - enfield, Bui. M, U. S. Dept. of Agric, 1903. Kansas City Flood of 1903. Eng. News, Vol. 50, p. 233, Sept. 17, 1903. Engineering Aspect of the Kansas City Floods, Eng. Rec, Vol. 48, p. 300, Sept. 12, 1903. Destructive Floods in the United States in 190k, E. C. Murphy, Water Supply and Irrigation Paper No. 147, U. S. G. S. Flood of March 1907 in Sacramento and San Joaquin River Basins, Cal., W. B. Clapp, E. C. Murphy and W. F. Martin, Trans. Am. Soc. C. E., Vol. 61, p. 281, 1908. The Ohio Valley Flood of March-April. 1913, A. H. Horton and H. J. Jackson, U. S. G. S. Water Supply Paper 334, 1913. Floods of March. 1913. Bui. Ohio State Board of Health, 1913. Floods of 1913 in the Ohio and Lower Mississippi Valleys. A. J. Henry, Bui. Z, U. S. Weather Bureau, 1913. The Rivers and Floods of the Sacramento and San Joaquin Watersheds, IT. R. Taylor, Bui. 43, U. S. Weather Bureau, 1913. Flood Control. Los Angeles. Cal. Rept. Bd. of Engineers, 1915. Southern California Floods of January, 1916, Water Supply Paper No. 426, U. S. G. S., 1918. Floods in the East Gulf and South Atlantic States, July, 1916, A. J. Henry, Monthly Weather Review, 1916, p. 466. Index to Flood Literature, E. C. Murphy and others, Water Supply Paper 162, 1905. Bibliography of Flood Literature. Report of Pittsburg Flood Commissibn, 1912. Monthly Index to Flood Literature, Bui. Carnegie Library of Pittsburg, 1908. ESTIMATING FLOOD FLOWS Determination of the Size of Seivers, R. E. McMath, Trans. Am. Soc. C. E., Vol. 16, p. 179, 1887. The Relation between the Rainfall and the Discharge of Seivers in Populous Districts, Emil Kuichling, Trans, Am. Soc. C. E., Vol. 20, p. 1, 1889. The^ Determination of the Amount of Storm Water, Prof. A. N. Talbot, Proc. Illinois Society of Engineers and Surveyors, 1894, p. 64. The Rainfall and Runoff in Relation to Sewerage Problems, W. C. Parmalee, Association of Engineering Societies, March, 1898, p. 204. Storm Floivs from City Areas and The Calculations, Ernest W. Clarke, Eng. News, Vol. 48, p. 386, 1902. Areas of Water Ways for Culverts and Bridges, G. H. Bremmer, Jour. West. Soc. Engrs., Vol. 11, p. 137, 1906. The Runoff in Storm Water Seioers, C. E. Gregory, Trans, Am. Soc. C. E., Vol. 58, p. 458, 1907. The Best Method for Determining the Size of Water Ways, Report of Com- mittee on Waterways, American Railway Engineering and Maintenance of Way, Bui. 108, p. 89, 1909. 596 Floods and Flood Flows. The Sewer System of San Francisco and a Solution of the Storm Water Flow Problem, C. E. Grunsky, Trans. Am. Soc. C. E., Vol. 65, p. 294, 1909. Runoff from Sewered Areas, L. K. Sherman, Jour. West. Soc. Engrs., Vol. 17, p. 361, 1912. Discussion of Rainfall and Its Runoff into Sewers, S. A. Greely, Jour. West. Soc. Engrs., Vol. 18, p. 663, 1913. Flood Flows, W. E. Fuller, Trans. Am. Soc. C. E., Vol. 77, p. 564, 1914. A Method of Determining Storm Water Runoff, C. B. Buerger, Trans. Am. Soc. C. E., Vol. 78, p. 1139, 1915. CHAPTER XX THE APPLICATION OF HYDROLOGY 261. Fundamental Consideration. — Hydrology and all other ap- plied sciences must be regarded as a means to an end and not as an end in themselves. The only reason for any engineering construction or for any engineering project is that as a result sufficient benefit will accrue to some individual or to some group of individuals to warrant the ex- pense involved. As a consequence of this truth, in the application of the principles of hydrology to the work of the engineer, all conclusions must be modified by the various factors which influence each particular project for the utilization or control of water. In general, the factors to be considered in addition to or concurrent with the principles of Hydrology are as follows : I. Available Funds: Sufficient funds must be available to meet the cost of the project. (a) Amount will modify possibilities, extent and character of en- tire development. (b) Source, taxation, special assessment, bonds, stocks, voluntary contributions. The possibility of securing funds by taxation and assessment depends on the laws of state, and the amount which may be raised by this means depends on the assessed valuation of the property to be taxed for the improvement. The possibility of financing by sale of stocks and bonds depends on the value of the property involved in the project, the laws under which they may legally be issued and the income which may be earned by the property or the returns which may accrue from legal as- sessments. II. Purpose Served: The project must serve some useful purpose. (a) Public service (water supply, water power and navigation). (b) Maintenance or improvement of sanitary conditions and pub- lic health (sewerage, drainage). 598 Application of Hydrology. (c) Betterment of physical conditions and increase in real estate values (irrigation and drainage). (d) Protection of life and property (flood protection). III. Physical Conditions: The conditions which obtain should be favor- able to moderate cost, safe construction, reasonable mainte- nance and free from serious contingencies. (a) Methods, materials, equipment and machinery available for the proposed development. (b) Comparative security of structures and methods available. (c) Comparative economy of various types of structures and methods. (d) Contingencies of construction, maintenance and operation. IV. Economic Considerations: A comparison of costs and benefits. The benefits from the project must equal or exceed the costs. (a) Costs. Capital Costs : Real estate, Construction, Interest and De- velopment expense. Operation, maintenance and depreciation expense. (b) Benefits: Income from project, Increase in values (of real estate), Improvement in health and living conditions and Protection of life and property. When benefits can be estimated either as annual dividends or as in- crease in real estate values, a comparison of such benefits with the costs and contingencies involved, will furnish a fair criterion as to the ad- visability of the project. The maintenance or improvement to health and the protection of life and property cannot always be given a mone- tary value, but the desirability is easily established and the financial limitations are often quite obvious. The study of each of the factors above outlined requires technical training, knowledge and experience. The details are so numerous that only a few items can be discussed in order to give the student the idea of how various factors must influence hydrological deductions. 262. Applied Hydrology. — In general engineering work in which hydrology plays an important part may be divided into : I. Works for the utilization of waters ; and II. W r orks for the control of waters. In most projects, however, both utilization and control may be im- portant. I. Projects for the utilization of waters may be divided into : Water Supply. 599 A. Private and public water supplies for domestic and manufactur- ing purposes. B. Irrigation of agricultural land. C. Water power. D. Internal navigation. II. Projects for the. control of water may include : a. The drainage and sewerage of cities. b. The drainage of agricultural lands. ' c. Works for the flood protection of cities, communities and lands. In the following sections each of the principal classes of hydraulic work to which the principles of hydrology most directly apply is briefly considered, some of the main factors which may modify hydrological conclusions are briefly discussed, and an outline is given which con- stitutes an analysis of the main factors which should be considered in all projects of the class discussed. The table of literature that follows the chapter gives a few of the principal books and articles in which these matters are discussed at greater length. 263. Water Supply. — Water is primarily more essential than food, for distress will be entailed earlier from a scarcity or absence of water than of food. Both water and food must be available however if life is to be maintained in any locality. Every home, farm or community of any kind must be provided with water if it is to be even temporarily established. The securing of a water supply may therefore be con- sidered as the most important object of applied hydrology. In the application of hydrological principles to the problem of the development of a water supply two main questions are involved which are in turn greatly modified in their application by other variable con- ditions. These main questions are quantity and quality of the avail- able supplies. The question of quantity while no more important than that of qual- ity, is ordinarily the first to receive consideration, for in every prob- lem of water supply it is of primary importance that there shall be a sufficient supply for the purposes under consideration or the purpose must be modified if the quantity needed cannot be obtained. In de- termining quantity both present and future conditions must receive con- sideration (see Sec. 210, p. 473). A common error in the selection of sources of water supply has been the consideration of only the most obvious source and the neglect or elimination of other sources less obvious but possibly of greater relative importance. It is uniformly desirable that every source which will 600 Application of Hydrology. D,- Deep Sandstone We//s w/'th Independent Pumps to Reservo/r Pumping Sfof/'on • Dr///ed by /9I5 9 Dr/l/ed by /920 " Dr/l/ed by J950 3P Fig. 344. — Possible Sources of Water Supply for Rockford, Illinois. Water Supply. 601 Auburn St. • Wel/s Drifted by f9/5 © Wef/s Drifted by /920 O Wefts Drit/ed by f950 £.- Deep Sandstone We//s with Jndependen t Pumps to Main W-9-l We//s Drifted by /9/5 Wef/s Drifted by f920 Wef/s Drifted by /9SO DDDDQ nnnn Shaft and Tunnet System with Deep Sandstone Wefts Fig. 345. — Possible Sources of Water Supply for Rockford, Illinois, yield a sufficient quantity and which seems reasonably feasible of de- velopment should be considered. In considering such various sources it is necessary to take into account not only the quantity obtainable from each but also the methods by which each can be developed and 602 Application of Hydrology. made available and the expense involved in the same. This will neces- sarily include the consideration of such processes as may be necessary for improving the quality to make each source unobjectionable as a water supply for the use and purposes contemplated. It is quite ob- vious that in many cases sources which are possible will be shown on brief investigation to be impracticable on account of the expense or other factors involved. Such sources can then be eliminated from further consideration and only those sources which are fairly compara- tive or unquestionably desirable may be reserved for final consideration and analysis. 264. Comparison of Sources of Water Supply. — I. Sources. — As an example of the various sources and methods of development which are sometimes available, the main possible schemes for a water supply for Rockford, Illinois, are shown in Figs. 344 and 345. These schemes include four different sources, viz. : 1. Gravel water from the drift (Fig. 344A). 2. River water filtered (Fig. 344B). 3. Spring and creek water filtered (Fig. 344C). 4. Artesian water from the Potsdam and St. Peter sandstone, de- veloped by three different methods : a. By low lift pumps into a reservoir (Fig. 344D). b. By high lift pumps directly into the water mains (Fig. 345E). c. By a shaft and tunnel system pumping from the wells either into a reservoir by low lift -pumps or directly into the water mains by high lift pumps (Fig. 345F). II. Quality. In the comparison of these sources and methods of supply, quality must be considered and it is to be noted that in the Rock- ford problem the filtration of either the creek (Fig. 344C) or river (Fig. 344B) water was contemplated. The artesian water possesses the advantage of organic purity but is harder than the creek or river water. The gravel water is also open to the objection of still greater hardness. In some cases where the softening of the water is essential or desirable, the cost of softening should aJso be contemplated in such a comparison. III. Equipment. In the comparison of sources and methods of de- velopment, the type of equipment which is or may be made available for the development is an important factor which modifies : 1st. The reliability of the development. 2d. The capital cost of development. Water Supply. 603 3d. The cost of operation and maintenance. It is obvious that these factors cannot be discussed in detail in a text on hydrology, but it seems pertinent to point out that if a dependable source can be obtained of satisfactory quality and of a sufficient height to be supplied by gravity the cost of operation will be less, and there are many other advantages over a supply where machinery is necessary to produce the pressure at which the water must be delivered. On the other hand, the cost of development of the gravity supply, on account of distance from the source, may render the project too expensive for consideration, and the adoption of a pumping project may be necessary for financial reasons. Again, in pumping projects the relative reliabil- ity of the machinery to be used, the expense of operation, and the con- tingencies of maintenance may greatly modify the value of one source as compared with another. In the same way, the necessity of clarification, filtration or softening plants involves complications, contingencies and expenses which will materially modify the choice of a source. The selection of a source may also be greatly influenced by the necessity of storage and the sites available for reservoirs, each of which will affect the expense of de- velopment. The above comments will be sufficient to point out a few of the vari- ous modifying influences which must be considered in the selection of a source of public water supply in addition to the principles of hydrology which have been previously discussed. In general, the principal factors to be considered in every water supply problem are outlined in the following section. 265. Outline of Factors for Public Water Supply Investigation. — I. Purpose. 1. Uses of and necessities for water supply: A domestic, B manufac- turing, C sanitary, D agriculture, E fire protection, F ornamental. II. Supply. 2. Sources of water supply: A rain water, B rivers, C lakes, D ground waters. 3. Character of supply: A quantity, B quality. 4. Quantity: A population, past and prospective, B variation in de- mand, seasonal, hourly, fire, C regulation by storage. 5. Quality: A improvement of quality: (sedimentation, coagulation and subsidence, aeration, filtration, hardening, softening, sterili- zation). 6. Method of supply: A gravity, B pumping. 7. Character of service: A constant, B intermittent, C high pressure, D low pressure. 604 Application of Hydrology. III. System. 8. Pumping plants: A primary and secondary pumping, B sources of power (water, coal, gas, oil, wind, electricity) C accessories (buildings, boilers, producers, motors, pumps, governors, relief valves). 9. Aqueducts, tunnels and conduits for collection and transmission (concrete, masonry, wood, iron). 10. Pipes, distribution: A cast iron, B wrought iron, C steel (riveted, spiral riveted, welded), D wood, E lead. 11. Accessories: A hydrants (gate or valve), nozzles (single, double, steamer , B valves and valve boxes, C air valves, D relief valves, E service meters. 12. Appurtenances: A filters and works for clarification, B reservoirs and works for storage, C elevated tanks and standpipe. 13. Design and Construction (present and future requirements), A water supply system, B pumping system, C power house, D reservoirs and basins, E filters and methods of clarification, etc., F trans- mission and distribution systems ( pipes, hydrants, valves, serv- ices, meters, plumbing). IV. Cost Estimates. 14. Land and water rights: A rights of way, B condemnation, C dam- ages. 15. Promotion, administration, engineering, supervision, legal expenses. 16. Time of construction and interest during construction. 17. Cost of structures: works and overhead costs. 18. Expense of developing business. 19. Cost of financing: Discounts, interest and sinking fund. 20. Maintenance, depreciation, operation, contingencies. 21. Estimated returns: gross and net profits from projects. V. Management. 22. Private or municipal ownership: A supervision, B office, C field, D plant, E books, F records, G rules and regulations. VI. Financial. 23. Financing: A development expense, B operation. C maintenance, D depreciation, E valuation. VII. Final Conclusion. 24. Comparative data, general discussion, recommendations. 266. Irrigation. — I. Application. — In arid regions agriculture can be carried on only by means of irrigation, and as the sources of water supply in such regions are from the nature of the regions very limited, the amount of land which can be made available for agriculture by irri- gation is also very limited and will become more and more important and valuable as the populations of such regions increase. In semi-arid regions crop failures in the absence of irrigation are fre- quent and irrigation is usually essential to profitable agriculture. When Irrigation. 605 irrigation is impracticable, dry farming methods, which are largely methods for the conservation of the soil water, are sometimes found feasible. In thickly populated humid regions intensive agriculture can be carried on only by means of irrigation, and in the suburban gardens surrounding large cities irrigation methods established at con- siderable expense are amply warranted. II. Extent. — The extent to which irrigation has been developed in the United States and the character of the various enterprises are in- dicated by the 1910 Report of the U. S. Census Bureau (Table 62) which however includes only the large projects of the Western States. TABLE 62. Extent and Character of Irrigation Enterprises in the United States in 1910. Acreage Acreage Capable of Acreage Character of Enterprise Irrigated Irrigation Included in 1909 in 1910 in Projects Carey Act 288,553 1,089,677 2,573,874 U. S. Reclamation Service 395,646 786,190 1,973,016 U. S. Indian Reservations 172,912 376,576 879,068 Irrigation Districts 528,642 800,451 1,581,465 Co-Operative Enterprises 4,643,539 6,191,577 8,830,197 Individual and Partnership En- terprises 6,257,387 7,666,110 10,153,545 Commercial Enterprises 1,451,806 2,424,116 5,119,977 13,738,485 19,334,697 31,111,142 An idea of the extent of work involved in the irrigation of this land can be gathered from Table 63 which gives the U. S. Census Summary of Irrigation Statistics for 1910. TABLE 63. Summary of Irrigation Statistics for the United States in 1910 {Not areas devoted to groioing rice) U. S. Census 1910. Total Acreage Irrigated 13,738,485 Total Acreage that could have been irrigated 19,334,697 Total Acreage Included in Projects 31,111,142 Number of Irrigation Enterprises 54,700 Length of Canals and Ditches 125,591 Length of Main Canals and Ditches 87,529 Length of Lateral Canals and Ditches 38,062 Number of Reservoirs __ 6,812 Capacity of Reservoirs 12,581,129 Number of Flowing Wells 5,070 Number of Pumped Wells 14,558 Number of Pumping Plants 13,906 Aggregate of Power used in Pumping 243,435 Acreage Irrigated with Pumped Water 477,625 Acreage Irrigated from Flowing Wells 144,400 Aggregate Cost of Irrigation Enterprises $307,866,369 Average Cost per Acre $15.92 Average Cost of Operation and Maintenance per year 1.07 including acres acres acres acres miles miles miles miles acre feet H. P. acres acres per acre 606 Application of Hydrology. Fig. 346 shows the location of the various irrigation enterprises of the U. S. Reclamation Service. Up to June 30, 19 16, there were 1,405,452 irrigable acres on these projects 922,821 of which were irrigated during the preceding year, and there had been expended on these projects a total of $149,786,534. The value of the total crops raised on all of the reclamation projects in 1916 was $32,815,972. It Pig. 346. — Principal Projects of the United States Reclamation Service. was estimated by Secretary Lane, in his annual report for the year end- ing June 30, 19T8, that there are 15,000,000 to 20,000,000 acres of arid land at present in the West for which water can be made available by proper conservation. III. Profit from Irrigation Developments. — Properly planned irri- gation enterprises have proved very profitable and have been of great value to promoters, irrigators and to the Nation. Suitable desert land which can be purchased under certain legal restrictions at low cost (sometimes as low as $1.25 per acre) becomes worth from $50 to $100 Irrigation. 607 per acre and upward when successfully irrigated. The costs of irriga- tion work vary widely from as low as $5.00 per acre to $100 per acre, and more. The margin of profit between cost of land plus a low cost of development and the high values of the best irrigated farms seems to offer opportunities for high returns, and these opportunities have induced promoters to undertake many ill advised, ill! designed and unfortunate ventures until at the present time (1919) irrigation pro- jects and irrigation securities are looked upon with suspicion by in- vestors. IV. Causes of Irrigation Failures. — Irrigation failures have resulted from many reasons but the most common cause of failure has been in- adequate water supply. 'In general these failures have resulted from dishonesty and incompetency in management or from mistakes in judgment which are exhibited in some of the following ways : Inadequate water supply Inadequate plans Poor construction Excessive cost Slow colonization Excessive distance from market It is apparent that an adequate supply of water for a suitable body of land is the primary requisite for successful irrigation, and most of the principles treated in the text covering the sources, qualities and quantities of water apply directly to this phase of the subject. An adequate and satisfactory supply is only one phase of the subject; the water must be properly conserved and transported to a suitable area to be irrigated. As the irrigation season is essentially the growing sea- son, adequate storage is often essential to store the supply during the months when it is not needed so as to concentrate the supply and adapt it to the largest possible area during the irrigation season. This neces- sitates an adjustment between the supply and storage, the loss from evaporation, seepage, etc., and the demand. The study of these factors in relation to the supply of Salt River Project of the U. S. Reclamation Service is shown in Fig. 347 as applied to the flow at the Roosevelt Dam and its normal application to 161,111 acres of this project. Seep- age must be considered not only as it affects the storage of water but also as it modifies the losses in transmitting it from reservoir to field. In many cases this transmission loss is enormous, and an adequate sup- ply at the field to be irrigated frequently requires twice the required amount delivered from the reservoir. Soil and subsoil conditions are 608 Application of Hydrology. therefore equally important to the water supply, for the soil must not only be suitable for irrigation purposes but the physical condition largely modifies the amount which must be supplied to meet the de- mand of the necessary losses in transmission and application. The topographical and physical conditions also affect the ultimate success for in many cases irrigation and especially over-irrigation results in a rise in the ground water and the deposit of alkali on the surface, and this necessitates the development of drainage or it results in the ruin of the land for agriculture, a consequence often apparently remote before land is irrigated but a consequence to be foreseen and considered in the intelligent development of plans for irrigation. Wafer Wasted over Sp/llway_ VV ' w \ \\ A f U76.JOO Acre feet \ \ v A \ ' J\ r «M *• \AS * ' ^^ \ _^_ -in Reservoir ' l A V A V I A 1 ^ t- ■\ / \ 3; \ Water A [\ Ueticient^ Demand Curve Fig. 347.---iAnalysis of Supply and Demand on the Flow of the Salt River as Modified by the Roosevelt Reservoir, when applied to 161,111 acres at the rate of 4.5 acre feet per acre.* In connection with the development of irrigation and drainage pro- jects a question of vital importance to financial success lies in the time which it takes to colonize the land and get it under successful cultiva- tion. Colonization depends not only on an adequate supply of suitable lands economically developed but a 1 so on the demand for such land, proximity to a market and other factors which influence or control the probable profit to the settler who is to make the project his home and on whom the ultimate success of the project must depend. Colonization is often a slow process and the profit which apparently should result in a great financial success may prove a financial failure on account of high carrying charges due to slow colonization. The *See Salt River Project, Arizona, Limiting Area of Land, Dept. of In- terior, U. S. Reclamation Projects, 1914, Washington, D. C. Irrigation. 609 average time to colonize various irrigation projects, based on experi- ence up to 1910 as derived from the 1910 U. S. census returns, is shown in Fig. 348. and the results anticipated and realized from such slow development is illustrated in Table 64. This table illustrates the possibility of failure through delayed colonization of a project which 80 70 \ I $.60 s x 50 ' <40 \*0 y. l /0 ^y vy <$A / $yy* 1 / /(\0 Az d / 1 /// vyA I /s 20 as 30 /3qe of f^rojeof in Years <40 4S SO Pig. 34S. — Diagram Showing Colonization of Average Irrigation Project Ac- cording to U. S. Census Returns of 1910.* might otherwise have been very profitable, and shows how factors other than those of hydrology or engineering must often influence and con- trol a project. 267. Outline of Factors for Irrigation Investigations. — I. Location of Project. 1. With regard to transportation and market, railroads, roads, near- est large cities and population, location of other projects, com- petition for sale of lands and sale of produce. *See Eng. News, Vol. 76, p. 202. Hydrology — 39 610 Application of Hydrology. -Ki s * - -T3 ?ss "cp s § 2 o ^* o Cs rt .2 S o « ■U6C° U S 3 ^ qj a So 3-2«f <2 I SS3 — :I. - &r r- g 3 OB "3 "5 § '* a 5H2 el ..80S 31 * _ ^ Jill >s 71 m = w c! a a a p a at 1-1 c3 6 5 — = ;^i?i:i-^ x, t- .- Ti -1 -r 1— - 1— t t : cc l - ~ CD CD T. I - ~ 1 1O t— Cft ~ ' ■d 53 ifl r^ x — or, 1 ooowHOcc-rfu- x ci cm ~f -"J* -f * t— * co cc to o ~- cm o"©* w D-* co i r* oc c th o 's' \t. — "»n © -r 'St^^t^tS^>oSco © 1 - , - -r -r m cd x — - cr ,— -~ •— — t - co x rit'LCitL-r- BS^; w ti o©8S©88§o~©©©o< oooo©oo©c>~-— - ©0©©©©©©©0©<: ■— * ■ — - — cc — - cr ~ ■ o © o o o O o © '- SS2S 55 = © *?22SS OOo © «C(M OS oaTofoo © © © or o o ~ cr © icrsfiinco^oo500t-«oif3-^*o: cm 1— © cr. cc l— = ccz zz-r*i:: 1.0 v: y cr — — co cd 1— 1 cc x h ci cc t> _ © © cd :i :: :: ■:: r :n-- r :iCi-i*. /i--'/r-cc'- OOcOCOMCT.COlf3(- NH^pt-WlOLOOCiOCCHMC'. 95 CM SO r>^ c- r H-r*iH a; cc © h -*7 av -r cc" lo re" c iYo ci co* © cm" co" _ co -j* lit; 1 - -r - o — © * * > r - x - - 1 - — t - 1 -r -r t— -— OoiOOCOOOoOOiOrHHWMkOt-v.N^t-CWLOOCTilO M CI C^f CM CM Cvf CM CO CO CO CO CO CO CO CO T ^Tj-'-^'Trir5 in IO CD CD !^ 03 CSo <50coOOcD^HM^ c .xf:e-f::i*cr/;ooO'tt O c co «5 th q * 1 - ri t* (, (- z 1 - t- c: x 1.- cc co — ~ r— O0000HHC0CCHL':cn^Ol--OailDI>flCrHlflC;M ' M CM N (M (N C < CD t— It- CO* • t- ci" co o^cm* '-/. 1 -* i © — " OOe^Oo^ooc ■ _— - ~ — -^~I~ - — — C: — c5 o o o o = — — o w o o ° ° ° ° o o o o o o o o o o o w — " c cr; rr* — cr —"——■ — — — " — o o © o o »n i-Om LOic t ~ 1 :ic ic'-'ic,' 1" 1 " '" 1.0 L ~ i~ icicw^ifl > SS5S5©^oo'-ic00C6 00 <& ci , , -f4 ^111^ o o o x ; _ ooog< '0* , © ©) © _ o o =, 3 o 5 o o o o > q o g S s 2 o < So - O*© ^3 . >°c : - r - - - 2 = i = =-5 = o-o 5oooooo oOo00ooooo oc ooosogo; oICXIc\lCNI T HNM-t^CD^OOCDOHNW^WCC^g^CH^,;-*^ Irrigation. 61 1 II. Physical Conditions. 2. Topography, geology, altitude, climate, temperature, rainfall (dis- tribution through years, variation, extremes). III. Land. 3. Quantity, availability, physical condition, nature. 4. Character of soil and subsoil: A alkali, B drainage, C seepage, D desirability or need of irrigation, E nature of vegetable growth, F clearing and grading, G ownership, H legal status, I value or cost. IV. Surveys, Topographic and Hydrographic. 5. Land surveys: A canal and ditch location, B farm unit subdivision, C town sites, D telephone lines, B roadways, F railroads, etc. G. Surface water: A flow of streams (records and gagings), B drain- age area (character and topography), C rainfall (comparison of rainfall and flow with other longer records), D reservoirs. 7. Ground water: A depth to water surface, B nature of water bear- ing strata, C data. 8. Water requirements: A estimated quantity, B development, C works needed (intakes, galleries, reservoirs). 9. Pumping water: A methods, B character of fuel, C cost. 10. Character of water: A salts contained, B silt in flood and normal flow, C character and effect of silt. 11. Water laws: A legal rights, B prior appropriations, C adjudications, litigations. V. Duty of Water. 12. Character of crops, water requirements of crops, irrigation season, load factor, soil conditions as affecting seepage and evaporation, drainage, methods of using, methods of distribution. 13. Losses in distribution, seepage losses, amount needed at source, amount needed at field, total water requirements. VI. Development Works. 14. Diversion works: A dams (dimensions, foundations spillway, over- fall, gates, apron). 15. Storage works: A reservoirs (geology, materials, seepage, cores, slopes, protection). 16. Controlling works: A head gates, B by pass, C overflow wasteways, D drops and chutes, E weirs, modules and meters. 17. Transmission works: A flumes, B tunnels, C canals, laterals and ditches (size, length, grade, character of soil, erosion, seepage, lining). 18. Transportation: A railroads, B roads, C bridges, culverts. 19. Pumping plants (condition, kind, class, power, fuel). 20. Drainage works: A ditches, B tile. 21. Auxiliary works, water power development (electric power, pump- ing). VII. Labor and Materials. 22. Methods: A contract, B day labor. 612 Application of Hydrology. 23. Labor: A nationality, B availability, C cost, D teams. 24. Material: A sources, B distance, C cost at source, D cost f. o. b. railway, E cost of transportation. 25. Machinery and equipment required: A class, B source, C cost, D hauling. VIII. Cost Estimates. 26. Land and water rights, cost of promotion, administration, engineer- ing, legal advice, litigation, condemnation, damages, time of con struction, interest during construction, cost of structures and works, overhead costs, cost of financing, sinking fund, payments, interest, colonization, estimated time required, cost of develop ment, interest, maintenance, depreciation and operation, esti- mated return and new profits from venture. IX. Final Conclusions. 27. Comparative data from other projects. 28. Recommendations. Fig. 349. — Power House and Dam Abandoned Because Possible Power Output was not Sufficient to.jPay for Operating. 268. Water Power. — The flow of streams is perennial. Coal, oil and gas are exhaustible. If the power of a flowing stream is developed for useful purposes, the country is richer, for something which other- wise would have been lost is saved and utilized ; and in general such saving' has also resulted in conserving an equivalent of fuel for the future which would have been lost. Water power is therefore an im- portant application of hydrology which demands greater consideration than it has received as yet. Water Power. 613 Agitation for so-called "conservation" has served to call attention to the desirability of the intelligent use of natural resources but has re- sulted in ill considered laws (1919) which have prevented development of water powers and resulted in a corresponding unnecessary use of exhaustible fuel resources. Intelligently developed, water powers are not only profitable to their promoters but from the very fact of their success show that they fulfill a demand which results in profit to their customers and a saving in the exhaustible natural resources and a development of the country. Water powers are not universally profitable. While the energy of running streams is a waste which a water power development is de- signed to prevent and to utilize, the expense of development is fre- Numbers represent percentages. Total represented S4,00O,OOO HP Fig. 350. — Percentage of Total Water Power in the United States Available in Each State. quently so great as to be unwarranted by the economy effected by the saving. Fig. 349 shows a 50 foot dam with power house which, while built in good faith, was so ill advised that it did not pay to operate it even after it was constructed and the investment incurred. The ma- chinery was removed through the opening in the power house wall and was installed on a larger stream. Many similar failures show the necessity of the consideration of all of the factors which when com- bined control the success of such projects. In water power projects, water is an essential feature, and the reg- ularity and quality of flow are important factors to investigate. (See Chapter XVI, p. 432). Head, however, is equally important and needs 614 Application of Hydrology. full investigation as at times of flood, head is often reduced and is es- sentially eliminated in many low head plants. The creation of head by the construction of dams requires an in- vestigation of the geological conditions which are favorable or un- favorable to safe and economical storage of potential energies above a given site, and the intelligent construction of works to control and utilize the same. Storage and pondage are also vital factors in water power utilization. In no case can water power be utilized at a continuous uniform load, and much power will be lost at times of low demands unless the water can be impounded at such times and utilized during the time of high demand. A comparative study of load factor, load demand, stream variation and storage possibilities is therefore often as important as qualitative studies of available stream flow. The distribution of the approximate 54,000,000 horse power of water available in the United States is shown in Fig. 350. Of this only about 5.000,000 horse power were developed in 19 12 so that water power projects affords a great field for engineering work. 269. Outline of Factors for Water Power Investigation. — I. Market or Demand for Power (proximity, nature and extent of market). 1. Special use, particular industry, general, wholesale or retail sale of power, character of load, load factor, power factor, seasonal loading. II. Physical Conditions. 2. Location: A topography, B geology, C climate, D rainfall (annual seasonal, variation), E temperatures (ice conditions), F fre- quency and character of storms (high winds, lighting) G earth- quakes. III. Hydrographic and Topographic Surveys. 3. Streamflow (annual, monthly, daily, gagings and records). 4. Plowage, storage and pondage (desirability, feasibility, effect). 5. Canals (location, excavation, construction, seepage, etc.). 6. Riparian lands, structure sites, railroads, transmission and tele- phone lines. 7. Head (amount and variation under high, low and medium flows). 8. Power (amount available, variations, amount desirable to develop, load factor). 9. Auxiliary power (necessity, probable amount, source, fuel cost, etc., effect on cost of delivered power). 10. Ultimate capacity and provisions for future growth of development. IV. Water Power Laws. 11. Water rights, flowage rights, condemnation, privileges, damages, litigation. Water Power. 6 1 5 V. Development. 12. Land: A site, B flowage, C rights of way, D roads, E bridges. 13. Dam: A foundations, B flood capacity, C spillway, D locks, E gates, F sluices, G fishways and logways. 14. Headrace: A capacities, B loss of head, C headgates, D canal, E tunnels, F soil, G erosion, H silt, I lining, J grade, K racks, L gates, M penstock (open, closed). 15. Power house and substations: A foundations, B type, (fireproof, wood, iron), C design (windows, doors, roof, floors, walls, gal- leries, rooms, stairways, heating, plumbing, water supply). 16. Tailrace: A capacity, B permanency, C loss of head, D soil and material, E lining, F silt. 17. Equipment: A turbines, B generators, C governors, D exciters. E switchboard, F lightning arresters, G transformers, H regula- tors, I oil purification, J gate operating machinery, K cranes. 18. Transmission: A line losses (distance, voltage, transformation, amount of power), B conductors (material, insulation, stringing and sagging, ground wires), C type (wood pole, steel pole, steel towers, durability, foundations, painting, galvanizing). VI. Labor and Material. 19. Work done by contract or force account: A labor (nationality, availability), B teams, C construction plant, D cost. 20. Material: A sources, B transportation, C distance, D cost. 21. Machinery for construction purposes: A kind, B availability, C cost. VII. Cost Estimate. 22. Water rights, real estate, flowage, rights of way, promotion, ad- ministration, engineering and legal expenses, time of construc- tion, interest during construction, cost of construction and over- head, cost of financing, interest, discounts, sinking fund, pay- ments, maintenance, depreciation, operation, taxes, cost of power, load, load factors, cost compared with power costs of plants used or which may be used in territory, cost of development of market, contingencies of construction, development and operation, dam- ages, benefits, returns, profits. VIII. Financing. 23. Common stock, preferred stock, bonds, securities, market, discount. IX. General Conclusions. 24. Comparison with data from other developments, adequacy of works, conclusions, recommendations. 270. Internal Navigation. — In the early development of a country the navigation of the interior waters may be of the utmost importance as the only practicable method of transportation. With the growth of the country and the increase in importance of rapid communication and transportation, railways have largely displaced waterways in importance and in most countries waterways have assumed a second and very sub- 616 Application of Hydrology. Internal Navigation. 617 ordinate place. In the United States their practical importance has in many cases departed. In Fig. 351 are shown the navigable waters of the United States. There are about 25,000 miles of rivers in the United States that are now navigable for boats of various drafts and perhaps a further equal mile- age which can be made navigable. The Great Lakes are about 1,400 miles in length but furnish a much greater length of navigable waters. There are also about 2,100 miles of canals in the United States part of which are however not navigable in part at the present time. The American canal at the Sault St. Marie carries more traffic than any other waterway of equal length in the world. This is because it controls the line of transportation from the iron mines of Minnesota, Wisconsin and Michigan to the furnaces along Lakes Erie and Michi- gan and of Ohio, Pennsylvania and Illinois. The great traffic over this short canal is unusual, as noted, and cannot fairly be used as an argument in favor of improving waters along lines on which no natural demand for navigation transportation exists. With further development and a growing demand for cheap trans- portation of bulky commodities, it is not inconceivable that the im- portance of internal waterways may increase in the future, but that they will, in the United States, ever again even approximate the im- portance of railways is hardly conceivable. What the future may de- velop with growth in population and increase in the cost and value of fuel and in labor difficulties can only be surmised. In late years there has been an attempt to arouse public interest and to create a public sentiment favorable to an immediate development of interior waterways. The more general, development and utilization of internal waterways in Europe has been used as an argument in favor of the general development of waterways in this country. It is im- portant to note, however, that there are already available in the United States more miles of navigable waters than in England, France, Bel- gium and Germany combined (see Table 65) and that the desirability of development of these resources in this country is purely a question to be determined from our own conditions. In the investigation of such problems their economic bearing should be determined as with all other problems, and no scheme for development should be advocated or adopted unless it can clearly be shown that its importance to the country will warrant the expense involved in construction, operation and maintenance. 618 Application of Hydrology. TABLE 65. Relative Length in Miles of Waterways and Railways in Various Countries of Europe and in the United States in 1905. Canalized Total Total Rivers River Canals Waterways Railroads England and Wales 812 1,312 1,927 4,053 France 796 970 1,777 7,485 2,445 Belgium 75 307 334 1,016 2,873 Germany 1,948 425 895 6,200 33,730 United States 26,400 1,410* 2,190 30,010 222,571 271. Outline of Factors of Navigation — Rivers, Canals and Har- bors. — I. General. I. Necessity, desirability, feasibility, benefits, tonnage carried or esti- mated, competition. II. Physical. 2. Location: A topography, B geology, C climate, D rainfall variations and extremes, E temperature (ice, anvigation season), F storms, G earthquakes. III. Water Supply. 3. Streamflow: (gagings, records, storage, equalization of flow, varia- tion of flow). IV. Water and Navigation Laws. 4. Riparian rights: A rights of way, B condemnation, C litigation, D benefits and damages. V. Development. 5. Surveys, hydrographic: A gagings, B soundings. 6. Surveys, topographic and land : A rights of way, B sites, C canal and channel locations, D flowage. 7. Dams: A foundations, B storage, C regulation, D wing dams. 8. Harbors, wharfs, jetties, piers, lights, channel marks, warehouses. 9. Locks: A size of vessels, B lift capacity, C gates, D time of operat- ing, E lock operating machinery. 10. Equipment: A towing equipment, B lighting, C power (transmis- sion, cost), D loading and unloading machinery. II. Channels: A excavating, B dredging, C class of machinery. VI. Labor and Material. 12. Method: A contract, B force account. 13. Labor: A nationality, B availability. 14. Material: A sources, B availability, C transportation, D distance, E cost. 15. Construction plant and equipment: A nature, B cost. VII. Cost Estimates. 16. Promotion, administration, engineering, legal, time of construction, interest during construction, construction and overhead costs, financing, appropriations, bonds, discounts, interest, sinking fund. *Great Lakes. sewerage. 619 damages, benefits, tolls, maintenance, depreciation, operation, taxes, contingencies. VIII. Financing. 17. Appropriation, stocks, bonds, securities, market values. IX. General Conclusions. 18. Comparisons, discussion, financial returns, recommendations. 272. The Sewerage of Cities. — Of projects for the control of water those for the drainage and sewerage of cities are perhaps the most common and of the most general importance. The overflow of storm waters, even for brief periods, may be highly objectionable in a village and not at all permissable in cities or large communities, while such occurrence in the country though undesirable may not be of sufficient importance to warrant an expensive remedy. In the country, or even in the village community, the vault or cess pool while objectionable may temporarily serve the purpose of disposal of household waste. In cities, with public water supplies, the waste waters are increased in quantities and if cess pools are used they would soon saturate the soil with filth and create unhealthful conditions. Sewers therefore become essential for the conveyance of such wastes to points where they may be discharged without serious consequences or where they may be treated and their injurious characteristics removed before they are discharged into surface waters. 273. Outline of Factors of Sewerage Projects. — I. Purpose. 1. Uses and necessities of system, sanitation and removal by water carriage of domestic and industrial waste and storm water. II. Source and Amount of Sewage. 2. Domestic: A quantity, B population present and prospective, C amount of water supply, D probable infiltration from ground water. . 3. Industrial wastes: A quantity, B character of industry (dye works, tanneries, etc.). 4. Storm water: A quantity, B rainfall, C drainage area, D character, E records and gagings, F comparisons with similar places, G run- off formulas. III. System. 5. Gravity flow, pumping (source of power, cost). 6. Sewers: A conduits (concrete, masonry, clay, metal), B capacity, C grade, D outfalls, E intercepting, F overflow. 7. Accessories: A manholes, B catch basins, C lamp holes, D vents, E traps, F pumps and ejectors, G plumbing. 8. Plant, A treatment (clarification, purification), B pumping. IV. Disposal. 9. Dilution in stream: A stream flow (records and gaging). 620 Application of Hydrology. 10. Broad irrigation. 11. Settling and screening. 12. Treatment: A septic, B filtration (sprinkling and contact niters) (activated sludge, D chemical reduction (trade waste), E sterli- zation. 13. Sludge: A incineration, B fertilizer. V. Ownership and Management. 14. Usually municipal ownership. Fig. 352. — Swamp Lands of the United. States. VI. Cost Estimates. 15. Promotion, administration, engineering, supervision, legal expenses, time of construction, interest during construction, cost of con- struction and overhead, cost of financing, bonds, discount, inter- est, sinking fund, damages, benefits, maintenance, depreciation, operation, contingencies. VII. Financial. 1G. Tax roll, special assessment, assessed valuation, bond limit, inter- est, maintenance, depreciation. VIII. General Conclusions. 17. Comparisons, discussion, recommendations. 274. Drainage. — For successful agriculture too much water is quite as detrimental as too little. There are many lands throughout the world that are too wet, periodically overflowed or permanent swamp D rainage. 62 which cannot be used for agricultural purposes to advantage if at all under the present conditions. The description of swamp and wet lands in the United States is given in Tab 1 e 66, and the swamp areas in the United States east of the Rocky Mountains are shown graphically in Fig"- 35 2 - TABLE 66. Swamp and Wet Lands of the United States. STATE Alabama Arkansas Cailfornia Connecticut . . . Delaware Florida Georgia Illinois Indiana Iowa Kansas Kentucky Louisiana Maryland Maine Massachusetts . Michigan Minnesota Mississippi .... Missouri Nebraska New Hampshire New Jersey .... New York North Carolina North Dakota . Ohio Oklahoma Oregon Pennsylvania . . Rhode Island . . South Carolina South Dakota . . Tennessee Texas Vermont Virginia Washington . . . West Virginia . Wisconsin Total Permanent Swamp Acres 900,000 5,200,000 1,000,000 50,000 18,000,000 1,000,000 25,000 15,000 300,000 Wet Grazing Land Acres 59,200 50,000 [,000,000 10,000 50,000 9,000,000 100,000 156,520 20,000 2,000,000 3,048,000 3,000,000 1,000,000 500,000 100,000 200,000 59,380 100,000 1,196,605 5,000 326,400 100,000 1,000,000 50,000 254,000 1,500,000 100,000 639,600 1,240,000 15,000 600,000 20,500 947,435 2,000,000 100.00C 100,000 500,000 50,00C 1,000,000 ,000,000 52,665,020 6,826,019 Periodically Overflowed Acres 520,000 531,000 1,420,000 20,000 27,000 1,000,000 1,000,000 400,000 500,000 350,000 300,000 300,000 92,000 39,500 2,760,200 1,439,700 412,100 7,700 329,100 500,000 50,000 100,000 31,500 50,000 6,000 622,120 511,480 8,000 200,000 23,900 14,747,805 Periodic- ally Swamp Acre 5 ! 131,300 200 800,000 700,000 10,000 80,500 44,600 784,308 748,160 50,000 55,047 2,064 1,000,000 !60,000 1,766,179 Total Acres 1,479,200 5,912,300 3,420,000 30,000 127,200 19,800,000 2,700,000 925,000 625,000 930,500 359,380 444,600 10,196,605 192,000 156,520 59,500 2,947,439 5,832,308 5,760,200 2,439,700 512,100 12,700 326,400 529,100 2,748,160 200,000 155,047 31,500 254,000 50,000 8,064 3,122,120 611,480 639,600 2,240,000 23,000 800,000 20,500 23,900 2,360,000 79,005,023 Drainage engineering varies in character from the simplest construc- tion of a tile drain or open ditch from a single farm to the most exten- 622 Application of Hydrology. sive projects involving perhaps, as in the case of the Florida Everglades, the drainage of thousands of acres by the construction of large canals. Such projects sometimes entail the diversion of head waters from the land to be drained and the construction of dams and levees to prevent the inroad of the sea or the overflow of rivers which adjoin the lands to be reclaimed, protected or improved. The irrigation of extensive areas of land commonly involve the neces- sity of the drainage of the lower lands which are injured by seepage from the ditches and higher irrigated areas. This is commonly the re- sult of over-irrigation and can be modified and minimized but not wholly prevented by the intelligent use of irrigation water. The ex- tent of the injury to the lands of the U. S. Reclamatation Service (in 1916) from this cause is shown in Table 67. TABLE 67. United States Reclamation Projects Estimates of Seepage and Summary of Drainage Work to June 30, 1911. rt a 5 k 2 °fi.'A 0> C C +J nj !■•■<-> Sh * hO- | " O « DRAINS a. *°<& ; ?\s» &_, \> A * ^ x ^. ■p x ^. Ci. '^ * ♦ X * A ^ "W x q* CL V ^ A* -* OQ X ? .^. V * O iOo. '- ^ ^ L ^ Cu -X° ~* ' ■^