LIBRARY OF THE UNIVERSITY OF CALIFORNIA. Class SENEBAL THE ENGINEERING RECORD SERIES WATER-WORKS FOR SMALL CITIES AND TOWNS BY JOHN GOODELL -TB R A .=? or THE ,. UNIVERSITY or THE ENGINEERING RECORD NEW YORK COPYRIGHT, 189$ BY THE ENGINEERING RECORD Introductory Note* The following notes on small water-works have been compiled to meet the desire for such information which is shown by letters addressed to "The Engineering Record." The book contains no new theories and no references to methods of construction or de- sign which have not proved satisfactory in actual use. As an offset to this lack of originality there will be found in the follow- ing pages considerable information never before collected in a single volume, and troublesome to obtain elsewhere. The editing of this material has been done with the idea of making the result of service to water-works trustees as well as superintendents and engineers; this will account for the attention paid to some details which technically educated officials may consider very elementary. 1 I 5779 CONTENTS. Paga Chapter I. Surface Water. The Yield of Catchment Areas Gauging Stream Flow The Meaning of Water Analyses 9 Chapter II. Earth Dams. Clay Gravel Masonry Core Walls Water in Earthwork Cross-section of the Embankment Starting the Core Wall. 23 Chapter III. Minor Details of Reservoirs. Outlet Pipes Gate-HousesWaste-Weirs 39 Chapter IV. Timber Dams. Brush Dams Crib Dams foamed Dams 52 Chapter V. Masonry Dams. Foundations Materials Earth Backing Design Specifi- cations Rock-Fill Dams 61 Chapter VI. Special Features of River and Pond Supplies. Head- Works Effect of Storage on Water Odors in Water. 81 Chapter VII. Ground-Water Supplies. Methods of Collecting Ground Water Quantity of Ground Water 88 Chapter VIII. The Utilization of Springs. Springs in Plains Hillside Springs 93 Chapter IX. Open Wells 101 Chapter X. Driven Wells. Sinking Wells Air in Wells Well Specifications 109 Chapter XI. Deep and Artesian Wells. Sinking Wells Specifications Yield of Wells Quality of Ground Water . . 123 8 CONTENTS. Chapter XII. Pumps. Steam Consumption Power Pumps Details of the Water End Special Power Pumps 138 Chapter XIIL The Air Lift 157 Chapter XIV. Pumping Stations 165 'Chapter XV. Intakes and Intake Pipes 174 Chapter XVI. Clarification and Purification of Water. Turbidity Slow Sand Filters Mechanical Filters 182 Chapter XVIL The Pipe System. Flow of Water in Pipes Data Concerning Pipe and Acces- sories Submerged Pipe Clay Pipes and Open Channels . . . 196 Chapter XVIII. Service Reservoirs and Standpipes. Concrete-Lined Reservoirs Asphalt-Lined Reservoirs Standpipes and Water Towers Substitutes for Standpipes. 218 Chapter XIX. The Quantity of Water to be Provided. Relative Capacities of Small Works for Domestic Supply and Fire Protection The Influence of Small Street Mains Fire Streams 251 Chapter XX. The Water-Works Department. Financial Considerations Checking Waste Keeping up the Works 263 Alphabetical Index 283 WATER-WORKS FOR SMALL CITIES AND TOWNS. CHAPTER I. SURFACE WATER. By surface water is meant the water discharged from the sur- face of a catchment area, as opposed to that collected from wells and galleries. Such surface supplies depend upon the rainfall for their existence, and upon the natural features of the watershed for their character. It is generally an easy matter to secure statistics of the rainfall in the neighborhood of most places large enough to have water-works, and from such statistics and an inspection of the catchment area the probable amount of water usually avail- able may be determined. It is sometimes possible, also to secure maps of the watershed, which are often of much value as indi- cating the sources from which a supply may be obtained; the maps of the national and state geological surveys are frequently used for this purpose. While it is the exception rather than the rule that a survey of a watershed for a small system has to be made with accuracy and be mapped subsequently, yet cases may arise when this is neces- sary, and consequently a few hints are given here as to the meth- ods now regarded as best adapted for such work. It is pretty gen- erally believed by engineers who have done most work of this sort that the quickest and cheapest method is by means of a transit having stadia hairs in the telescope, the notes being plotted in the field on a sketchboard. The accuracy of the stadia was definitely settled during the survey of the Mexican boundary a few years ago, and if the precautions are followed which are recommended in a paper on this survey by J. L. Van Ornum, Assoc. M. Am. Soc. C. E. (see the "Transactions" of the American Society of Civil Engineers, Vol. xxxiv., p. 259), the topography of a watershed may be taken with much dispatch and sufficient accuracy for all 10 WATER-WORKS MANUAL. purposes. It is unnecessary here to give instructions as to the method of making the stadia survey, but a few notes on the use of a sketchboard may be appropriate, as the published information on the subject is meager and not readily secured. The sketchboard is merely a portable drawing-board on which the transit and stadia notes are plotted in the field as fast as prac- ticable. These notes furnish the location and elevation of all the leading features of the tract surveyed, and it is an easy matter for a draughtsman to sketch in the intervening contour lines by eye. One of the best sketchboards known to the writer was designed by A. R. Paddock, and is described in "The Engineering Record" for October 31, 1891, and February 6, 1892. The top is a wooden frame, into which fit four small wooden squares. The top of each square is covered with drawing-paper, which is turned over the edges and fastened to the lower surface. When the four squares covered in this way are placed in the frame a uniform paper sur- face of about 310 square inches is furnished f or sketching. When- ever the plotting approaches one edge of the board, as the east, the two eastern sections are transferred to the west edge and two fresh ones put in their place. The field notes were plotted on these tables in two ways. Some were laid off by using the magnetic bearings and marking off the points with a card protractor having a scale on one edge, while others were fixed by using a simple ali- dade consisting of a metallic triangular scale with a pair of sight- ing wires attached. The cost of a table of this sort was about $11. On the surveys made in 1884, under the direction of Rudolph Hering, M. Am. Soc. 0. E., in connection with his studies for a new water supply for Philadelphia, the advantages of the sketch- ing-table and transit method of surveying were found to be as follows: "First, the immediate detection and correction of errors in angles or measures while plotting, thereby saving delays and inac- curacies in the office work; secondly, the drawing and sketching of the contours in greater conformity with the shape of the ground while viewing it, and saving the measuring of many points that would be necessary in the case of office plotting; thirdly, the possibility of putting in minor points by sight intersections, as on a plane table; and fourthly, of having the map so far completed in the field that it requires little more than an adjustment and transfer by means of blackened paper to be in its proper form WATER-WORKS W&NV&L. It and place upon the section maps. The results have so far been very satisfactory, the plotting shows a high degree of accuracy, and the gain in time has been considerable. In the field the plot- ting parties could, on similar territory, of course not cover as much ground per week as the others, their gain being in office work. In fair country it was found possible readily to survey and plot in the field, to a scale of 400 feet to 1 inch, 3 square miles per week, the party consisting of the engineer and one rodman." (Re- port by Rudolph Hering.) On this survey the field table was 15 inches square, and had a universal joint and tangent screw. It rested on a very light tripod. The sheets of paper were ruled to quarter-inch squares, each square representing a 100-foot square of land. Main lines were run with the transit by magnetic courses and stadia in cir- cuits of 1 to 3 miles, and these were immediately plotted to scale on the table standing beside the transit. The levels were taken by the transit, by spirit leveling and vertical angles, from bench marks established by a level party, and were plotted at once on the paper, so that the contours could be sketched in. Buildings, roads, and streams were located by transit angles and then plot- ted, or were sighted from the table, after leveling and orienting tt. Colored pencils were used to mark in certain features; blue for watercourses, green for the outlines of woods, and yellow for roads. Of course it is not always convenient to use this method of sur- veying, and when a sketching-table is not available a modification of the following method may be found advantageous. This method was also used under Mr. Bering's direction. The instru- ments employed were a transit, stadia rod, slope level, prismatic compass, and barometer. Main or base lines, with magnetic courses and stadia distances, were run over the territory, so as to form approximate quadrilaterals of about one-half to three- fourths square mile each. They were bounded by definite lines, as roads or streams, tied at the four corners. The position and elevation of high and low points was taken by magnetic and ver- tical angles, and stadia distances directly from the main line, if possible, otherwise a spur line was run to where they could be seen. In thickly wooded regions the topography was taken with the prismatic compass, slope level, and barometer. Buildings were located either by at least two magnetic angles from the base i2 WATER-WORKS MANUAL. line, or one angle and stadia measurement. Roads, streams, and such features were fixed in the latter way. Levels were carried in the manner mentioned in connection with the sketch-table method, and were generally found to check within a foot in a circuit of 2 or 3 miles. The vertical angles were reduced by nat- ural sines and cosines on the main lines, and by co-ordinate paper protractors as well on the laterals. All notes and sketches were entered in a transit-book. The amount of water that may be obtained from a catchment area is very \ariable and can only be estimated roughly. A small area, under about 2 square miles in extent, may be practically dry at tinier. Statistics compiled under the direction of the Boston Water Board show that from 40 to 50 per cent, of the rainfall has been collected, on an average, for many years on the watersheds under its control. These statistics are probably the most com- plete in this country, and on this account they are largely used in estimating the flow from catchment basins. The characteristics of the three watersheds controlled by the Boston Water Board are described as follows by Desmond FitzGerald, M. Am. Soc. C. E.: "The Sudbury River watershed has an area of 75.199 square miles; the Mystic, 26.9 square miles; and the Cochituate, 18.87 square miles. The Sudbury is hilly, with steep slopes. There are, however, some large swamps within its borders. The Cochit- uate, although adjoining the Sudbury, is entirely dissimilar. The slopes are flat and sandy. The surface is mostly modified drift, while the Sudbury is largely composed of unmodified drift. The Mystic watershed lies to the north of Boston, and about 30 miles distant from the other two sources, which are to the west of the city. Its surface is steeper than the Cochituate and not as steep as the Sudbury." The average monthly yield per square mile of these watersheds for a period of 13 years was as follows: Month. Gallons. Month. Gallons. January 37,387,000 July 7,491,000 February 55,056,000 August 11,399,000 March , . . . 71,226,000 September 10,242,000 April 49,107,000 October 16,797,000 May 30,406,000 November 24,787,000 June 14,975,000 December 34,128,000 These figures are interesting and valuable in many ways as il- lustrating the monthly variations in stream flow under conditions WATER-WOPKS MAX UAL. 13 that will probably be found to agree approximately with those in many other parts of the United States. The average rainfall at Boston for the last 75 years has been as follows: January, 3.98 inches; February, 3.78; March, 4.36; April, 4.06; May, 3.79; June, 3.27; July, 3.71; August, 4.39; September, 3.55; October, 3.84; November, 4.31; December, 3.96; total, 47 inches. In the design of water-works depending upon surface supplies averages are not of as much importance as minim urns, and on this account the Sudbury River statistics are of great value. They ex- tend back many years and contain records of two periods of re- markable drought. Engineers want to know the minimum quan- tities of water to expect from a watershed, and the following table is therefore given showing the daily flow from the Sudbury basin for different periods, the figures giving the daily gallons per square mile in the driest period of the given duration: Period. Gallons. Period. Gallons. Period. Gallons. 1 month 2 months. . . 3 months. . . 4 months. . . 5 months. . . 6 months. . . 44,000 64,000 95,000 118,000 131,000 143,000 7 months. . 8 months. . 9 months. . 10 months. . 11 months. . 1 year 147,000 181,000 219,000 312,000 409,000 497,000 2 years . . . 3 years . . . 4 years . . . 5 years . . . 6 years . . . 7 years . . . 687,000 764,000 735,OOU 769,000 803,000 839,000 The average flow from the Sudbury River watershed per square mile during the driest periods of five years or less has been, so far back as records have been kept, very much less than from the Croton watershed in New York, while the average flow for the whole 19 years of observation on both basins has been nearly the same. It is evident from the above table that if means can be pro- vided for storing the surplus water from a catchment area during the periods when the supply exceeds the consumption, it will be possible to satisfy daily drafts of many times the yield of the watershed during the driest periods that are liable to occur. In the "Transactions" of the American Society of Civil Engineers, Vol. xxvii., p. 265, Mr. Fitz Gerald gave a diagram of the storage capacity required to sustain drafts of 100,000 to 900,000 gallons daily from 1 square mile of watershed containing various per- centages of water surface. F. P. Stearns, M. Am. Soc. C. E., has prepared Table No. 1 for the same purpose, arranged in a some- what different manner and taking evaporation into account. The nature of the investigations upon which this table was 14 WATER-WORKS MANUAL. based was explained in "The Engineering Record" of February 24, 1894, and engineers who desire to study the matter farther are referred to that article and to the paper by W. Rippl entitled "The Capacity of Storage Reservoirs for Water Supply," which was published in the "Proceedings? of the Institution of Civil En- gineers, Vol. Ixxi., p. 270. Table No. 1. Showing the Amount of Storage Required to Make Avail- able Different Daily Volumes of Water per Square Mile of Water- shed (Estimating Land Surfaces Only), Collected for the Effect of Evaporation and Rainfall on Varying Percentages of Water Sur- face, not Included in Estimating the Area of the Watershed. fe *o 05 Storage Required in Gallons per Square Mile of Land Sur- face to Prevent a Deficiency in the Season of Greatest Drought When the Daily Consumption is as Indicated in the First Column, with the Following Percentages of Water Surfaces. 3 6 10 25 100,000 556,000 3,000.000 8,800,000 150,000 3,400,000 7,100,000 13,400,000 . . . 200,000 9,400,000 11,700,000 18,000,000 . . . 250,000 19,000,000 22,200,000 25,400,000 . . . . 300,000 29,800,000 33,000,000 36,100,000 400,000 52,000,000 54,400,000 57,500,000 . . . 500,000 76,500,000 77,300,000 80,300,000 . . . 600,000 102,000,000 104,600,000 107,100,000 112,800,000 . . 700,000 144,400,000 . 153,000,000 161,600,000 170,700,000 215,900,000 800,000 202,300,000 210,900,000 219,500,000 228,600,000 273,800,000 900,000 346,200,000 349,200,000 352,200,000 353,900,000 381,600,000 1,000,000 514,600,000 516,700,000 519,700,000 523,600,000 532,200,000 The manner in which the table is to be used can be most easily indicated by quoting from Mr. Stearns's explanation. "Let us assume that it is desired to know the yield of a pond having an area of 0.15 square mile and an available storage capac- ity of 225,000,000 gallons, which has draining into it 1.5 square miles of land surface. The amount of storage in this case would be equivalent to 150,000,000 gallons per square mile of land surface, and the water surface would equal 10 per cent, of the land surface. By looking in the column of the table headed 10 per cent., it will be seen that a storage of 1 50,000,000 gallons per square mile corresponds to a daily volume of between 600,000 to 700,000 gallons per square mile, or more exactly, by proportion, to 660,000 gallons, equal to 990,000 gal- lons daily for the whole watershed. The results obtained by this method will. in some cases be practically correct. In other cases WATER-WORKS MANUAL. 15 it will be necessary to take account of local conditions, prominent among which may be leakage past a dam, or filtration through the ground to lower levels; and the application of judgment will often be necessary to determine whether the watershed under consid- eration will yield the same or a greater or a less amount per square mile than that of the Sudbury Kiver." The more frequent problem, however, is to determine upon the amount of storage required to enable a definite quantity of water to be drawn from a given watershed. For instance, suppose 1,000,000 gallons a day are wanted from a watershed having a land area of 1.5 square miles. There is hardly a catchment area large enough to be considered as a collecting ground for water- works that has not some water surface, and Mr. FitzGerald says that in the use of such methods of estimating as are here consid- ered, it is of doubtful utility to consider anything under 2 per cent. In the present case it will be assumed that the only water on the catchment area is a brook of undetermined but small super- ficial extent; accordingly 2 per cent, will be assumed as the water area. The amount of water required per square mile of land area will be a little under 670,000 gallons. By interpolating from the table it will be found that the storage needed under these condi- tions will be about 136,300,000 gallons per square mile of land surface, or 235,000,000 gallons all told. Such a storage volume, however, would require a water surface of, say, about 0.13 square mile. This, however, is about 8^ per cent, of the total land area, and indicates that another computation will be needed. In view of the results of the first calculation it will be assumed that the land area is reduced to 1.4 square miles by reason of the construction of the reservoir, and that the water area is 10 per cent, of the land area. In this case, the draft per square mile of land surface will be a little over 700,000 gallons a day, and will require a storage capacity of 171,000,000 gallons per square mile, or 240,000,000 gallons all told. Hence such a reservoir under the conditions assumed may be considered adequate to supply the quantity of water desired. But such a reservoir might prove very undesirable from another point of view, even if a location for it can be found. It has been pointed out repeatedly that any attempt to store more than 700,000 gallons per square mile of watershed in arti- ficial reservoirs, under the conditions obtaining in the Sudbury 16 WATER-WORKS MANUAL. Kiver basin, will be very liable to end in failure from the fact that during several consecutive months the water level in the reservoir may be so low as to permit a growth of weeds on the exposed shores, which will cause a marked deterioration in the quality of the water. Mr. Stearns states that taking everything into account it may be said the greatest amount which can be made practically avail- able from a square mile of watershed does not exceed 900,000 gal- lons per day, and the cases are very rare in which more than 600,000 gallons per square mile per day can be made available when it is necessary to store the water in artificial reservoirs. Mr. FitzGerald states that it is impracticable to secure more than about 750,000 gallons daily per square mile of watershed contain- ing 10 per cent, of water surface. The reason for this limitation is that the levels in the reservoir should not be made to fluctuate too much and that the reservoir should not be drawn below the high-water mark for too long a time. The above method of estimating the amount of water which may be made available from a watershed is very conservative. IJ nder the conditions of rainfall and topography upon which it is based, it will be too conservative for most years. But a water famine is a serious affair, and it is well to provide against it. The modifications of the method to suit localities where the conditions of rainfall differ from those mentioned are matters of judgment for which no general rules can be given. It must not be forgot- ten, however, that because the discharge of small catchment areas is liable to so much greater variations than that of larger basins, it is highly important to avoid overestimating their yield in periods of extreme drought. Speaking generally, it may be said that unless a watershed is very mountainous, very flat, or very sandy, or unless the rainfall upon it differs considerably during a term of several years from the averages given in the preceding discussion, the determination of the available supply by the fore- going method will give results as nearly accurate as such estimates can be made. Moreover, the determination thus made will be free from the very frequent error of exaggerating the amount of water that may be safely counted upon. In some cases there may be a brook flowing from the watershed, and it is desirable to ascertain roughly how much water is passing in it. In such a case the cross-section of the stream should be WATER-WORKS MANUAL. 17 measured as carefully as possible at the lower end of the straight- cst and most uniform part. Then a distance of 100 feet should be measured back from the place where the cross-section was taken, and the number of minutes it takes several small pieces of wood to pass this 100 feet should be observed. In this way the surface velocity of the brook may be determined. Eight-tenths of this velocity, expressed in feet per minute, multiplied by the cross- section of the brook in square feet, will give approximately the discharge of the brook in cubic feet a minute. This method should not be used unless the 100-foot section of the brook is fair- ly straight and differs but little in its sectional area throughout the distance. Where greater accuracy is desired weirs must be employed. A Gauge Post. Weir FIGURE 1. - ARRANGEMENT FOR GAUGING BROOKS. rough weir can be made as shown in Figure 1 without much diffi- culty. The planks should be firmly bedded in the bottom and sides of the brook, and the three edges of the rectangular notch should be beveled off to an angle. The distance from the sides and bottom of the notch to the banks and the bed of the brook should be not less than three times the depth of the water above the lower edge of the notch. The bottom edge of the notch should be perfectly level. Care must be taken that water does not have an opportunity of leaking under or around the weir. Six feet or more above the weir a stake should be driven firmly in the bed of the brook. When this is done, which should be before the planks are put in place, the weir should be built up, and the ele- 18 WATER-WORKS MANUAL. vation marked very carefully on the stake at which water begins tc flow over the notch. Then a scale of inches should be marked on the stake with this point as a zero. If the work is well done this scale will enable the depth of water above the notch to be determined quite accurately. In order to determine the flow over the weir, take the reading in feet and decimals of a foot on the stake and then obtain from Table No. 2 the discharge in cubic feet per second over a weir 1 foot long for that depth. Multiply this discharge by the length of the notch in feet and the result will be the discharge of the brook in cubic feet per second. Care should be taken to make the notch of such a size that the flow through it will not exceed 6 or 8 inches a second, if possible. Notches 2 feet long are best with depths of water of 0.3 to 0.7 foot, 3 feet long with depths of 0.3 to 1 foot, and weirs 5 feet long with depths as high as 1.7 feet. The values in the table are to be understood as approximations, suitable, however, for the rough nature of such measurements as are here descibed: Table No. 2. Discharge of Weirs 1 Foot Long. Depth, ft 0.4 0.45 0.5 0.55 0.6 0.65 Discharge . . , . . . 0.836 0.998 1.167 1.345 1.531 1.724 Depth, ft 0.7 0.75 0.8 0.85 0.9 0.95 Discharge 1.925 2.133 2.347 2.568 2.795 3.028 Depth, ft 1.0 1.05 1.1 1.15 1.2 1.25 Discharge 3.267 3.511 3.761 4.016 4.277 4.542 Depth, ft 1.3 1.35 1.4 1.45 1.5 1.55 Discharge 4.812 5.087 5.367 5.051 5.940 6.233 Depth, ft 1.6 1.65 1.7 1.75 1.8 1.85 Discharge 6.530 6.832 7.137 7.447 7.760 8.077 Depth, ft 1.9 1.95 2.0 Discharge 8.398 8.723 9.051 The quality of water from a watershed depends upon the popu- lation of the area, the number of swamps in it, and the nature of the rock formation over which the water passes. If limestone is common, the water is liable to be too hard, if there are swamps on the catchment area, the color is apt to be dark, and if the popu- lation on the watershed is more than about 300 per square mile, the stored water often proves troublesome from bad tastes and odors. "Shallow storage reservoirs, from which the soil and vege- table matter have not been removed, generally give trouble, and the large and deep reservoirs of the same character are by no means exempt/' The suitability of water for a town and municipal supply de- pends upon its freedom from sewage contamination, hardness, WATER-WORKS MANUAL. 19 color, odor, and taste. The direct sewage contamination of a sur- face supply rarely needs to be determined by analysis, as the in- spection of the watershed will indicate any sources of pollution. Where water is drawn from lakes and streams the aid of the chem- ist and biologist must be sought before judgment can be passed safely on any water. These analysts have generally printed direc- tions as to the methods by which samples are to be collected, so it is hardly necessary to give such instructions here. In sending the samples full information should be furnished regarding the nature of the surroundings of the places where they were ob- tained, as the analyst is thereby enabled to come to more definite conclusions regarding the availability of the source for the pur- poses proposed. Few water commissioners and superintendents are not confront- ed sooner or later with apparently formidable tables of chemical analyses, so it may be well to point out what such analyses mean The source of the most serious pollution of water is organic mat- ter. This may be present as living organisms and the product of organic life, or the matter may be present in various stages of de- composition. It is customary to classify the condition of the or- ganic matter by means of the condition of the nitrogenous 'organic matter. In this way the albuminoid ammonia is taken as an indication of the amount of undecomposed organic mat- ter. When decomposition has begun, its extent is indicated by the presence of so-called free ammonia. Further changes result in altering the free ammonia to nitrites, which finally become ni- trates, the last stage in the process of alteration by which organic matter is converted into a form suited for assimilation into new organic matter. It is imprudent to state that because a water con- tains unusually large amounts of any of these compounds of nitro- gen that it is necessarily polluted. The signification of each com- pound may be stated briefly as follows, it being understood that only surface waters are now under consideration: Albuminoid ammonia was formerly considered as an indication of the presence of an equivalent amount of organic matter liable to decay, but within recent years it has been found that this it not necessarily so. The lesson to be learned from this compound is indicated most clearly by successive analyses of a water, for if the albuminoid ammonia remains unchanged for months without de- veloping free ammonia, a comparatively large amount may be 20 WATER-WORKS. MANUAL. harmless. This is especially the case with brown coloring matter which water dissolves from grasses, leaves and roots, according to Dr. T. M. Drown, who instances the very dark water of Acushnet River, the source of New Bedford's supply, as a good water con- taining enough albuminoid ammonia to be classed as polluted by most European standards. Free ammonia, so-called, is a characteristic ingredient of sew- age, but "the conditions which influence its development and ac- cumulation in natural waters are so various that one must be ex- tremely cautious in deciding what is the signification of its pres- ence in individual cases." If an analysis shows a large amount of free ammonia in a water from a catchment area having dwellings upon it, further investigations should be made into the causes of its presence. Nitrites are compounds of much interest, as their amount is gen- erally found to vary less with the seasons than the other organic derivatives, and they are therefore a better index of sewage pollu- tion. "High free ammonia and high nitrites together are charac- teristic of recent pollution, and when they are uniformly high in a surface water they point to continuous pollution." oSJitrates indicate the complete change of organic to inorganic matter, and their importance can only be settled satisfactorily when the source from which they were derived is known. The organic matter that is discharged into a water is rarely dangerous if it is given time to change to nitrates, but the disease germs that may have been discharged at the same time may be still a source of danger when the chemical changes are over. Chemical analy- sis, by indicating the amount of albuminoid and free ammonia, nitrites and nitrates, points out the probability of such germs being in the water and the time that has elapsed since they were discharged into it. The time is probably least when the albumin- oid ammonia is high, and greatest when the nitrates are high in the analysis. Chlorine is a valuable indication of sewage contamination. The amount to be found in unpolluted water varies widely; in Massa- chusetts it decreases as the distance from the seashore increases, and it is highly desirable to know what is the normal amount in unpolluted water in a given region before deciding upon the sig- nification of the amount shown by analyses of samples of water of unknown character from the same locality. The chlorine in WATER-WORKS MANUAL. 21 the reservoirs of the Boston water system is found to vary directly with the population upon their respective watersheds. High free ammonia, high nitrites, and high chlorine are considered to af- ford complete proof of pollution by sewage. Dr. Drown has pointed out, however, that when the chlorine is not much above the normal in waters containing high free ammonia and nitrites the inference is that the pollution comes from farmyards or manured fields, a distinction that it is often important to make. Table No. 3, giving a number of analyses of waters, shows what is meant by high and low amounts of the various compounds re- ferred to. It is taken from the Twenty-second Annual Report of the Massachusetts State Board of Health, and the figures stand for parts per 100,000. The first six analyses are of unpolluted waters, while the last five are of polluted waters. Table No. 3. Water Analyses. Free Albuminoid Ammonia. Ammonia. Nitrates. Nitrites. Chlorine. 1 ..... ...... 0.0000 0.0022 0.0060 0.0000 0.08 2 0.0702 0.0030 0.0030 0.0006 0.10 3 0.0000 0.1252 0.000.0 0.0000 0.10 4 0.0130 0.0333 0.0250 0.0001 0.16 5 0.0000 0.0136 0.0050 0.0000 0.63 6 0.0000 0.0152 0.0060 0.0001 2.10 7 ..... 0.0124 0.0284 0.0130 0.0000 0.19 8 ..... 0.0000 0.0196 0.0550 0.0004 0.54 9 ..... 0.0016 0.0198 0.0200 0.0004 0.58 10 ..... 0.0000 0.0262 0.0170 0.0010 2.09 11 0.0664 0.0263 0.0800 0.0025 2.41 The hardness of water is expressed in the analyses of the Massa- chusetts State Board of Health by comparing it to the amount of carbonate of lime that would have the same effect in an otherwise pure sample. A hardness of 2 means that the effect of the soap curdling substances in the sample would be produced by water containing 2 parts per 100,000 of carbonate of lime. This prop- erty has little hygienic signification, but it is important in other respects, for if the substances causing it are present in large amounts the water causes trouble in steam boilers. Frequent ref- erence is made in reports and books on water supply to Dr. Clark's scale of hardness. In this scale each degree represents the hard- ness of water containing the equivalent of one grain of carbonate of lime to the imperial gallon; 22 degrees of hardness is therefore that of an imperial gallon of water containing soap-curdling mat- ter producing the same effect in it as would 22 grains of lime. Waters of more than 5 degrees of this scale are usually considered 22 WATER-WORKS MANUAL. hard. Chemists distinguish between permanent and temporary hardness, the latter being the amount or number of degrees that may be removed by boiling. A water temporarily hard will give a sludge or mud in a boiler, which is easily cleaned out, while one permanently hard will produce the hard scale which boiler-tenders find so difficult to remove. The chemist who makes an analysis of water should always be requested to supply an interpretation of it so that the results of his work may be understood by persons without chemical training. If his report is properly prepared the foregoing hints will prob- ably enable its significance to be understood readily. The reports of bacteriological analyses should always be accompanied by a statement as to what they go to prove, as bacteriology is a science of such rapid progress to-day that only a specialist's interpretation of an analvsis is of much value- CHAPTER II. EARTH DAMS. An impounding reservoir is often regarded as nothing but an artificial lake, to be formed in the cheapest possible manner, but if the water is to be used for domestic purposes, such a view will be liable to lead to trouble. The dam itself, if poorly designed or built, may be a source of danger to people living below it; if it is not carried into the underlying strata and into the banks so as to prevent leakage, considerable water may be lost; if the surface soil is allowed to remain, the quality of the water may be very bad at times; if there are places along the borders of the reservoir where the depth of water is shallow, weeds may grow and injure the quality of the water when they decay; if the reservoir is so located that the disposition of the strata under and around it is unfavor- able, the water may leak out and the reservoir prove little better than a strainer, provided the bottom is not made tight in some way. These are all important matters to be settled before begin- ning work, and the history of water-works construction in this country shows that much money has been wasted and much an- noyance caused by failure to take them into consideration. Fairly water-tight dams can be made of many materials which are unsuited for use in reservoir embankments. A manufacturing canal at Nashua, N. H., has a bank composed of nothing but pure sand, through which in its natural condition water passes freely. In the 60 years this canal has been in service the sand has become silted with fine material deposited from the water, and it is now practically tight. The old Middlesex Canal in Massachusetts had banks of loose gravel which must have allowed large quantities of water to pass early in its history, but the sediment in the water filled the interstices and finally made the banks tight. Reservoir embankments of sand are not uncommon in India, and the con- struction of one of the best of these is described very fully in the "Proceedings" of the Institution of Civil Engineers, Volume cxv., by Col. S. S. Jacob. According to Mr. Albert F. Noyes, M. Am. 24 WATER-WORKS MANUAL. Soc. C. E., a reservoir embankment about 16 feet high has been built of fine sand, the slopes being 1| to 1 and covered with the turf taken from the ground. There was no appreciable leakage of water. A section of the bank was finally carried away, the break being caused by a woodchuck hole. It was repaired by filling in the opening with the same kind of material that was washed away, and then facing the inside slope with hardpan, a kind of clay gravel, put on in thin layers until a total thickness of 2 feet was obtained. All stones above 2 inches in diameter were picked out carefully, and the layers were compacted by spading rather than by rolling or tamping. This facing was covered with 4 inches of broken stone and a layer of riprap 12 to 14 inches thick,, It was found best in making such an embankment to have the material slightly damp but not wet, and to use no water while rolling the layers. In spite of the favorable experience with some dams made of sand, it cannot be regarded as a material suitable for such works, when anything better can be secured at a not prohibitory cost. When it comes to considering the other varieties of earth used for embankments, there is a very troublesome obstacle to collect- ing information viz., the lack of uniformity in the use of the terms applied to the various materials. There are a few rule-of- thumb practices regarding earth in which technical terms are not involved, among them is one adopted in the neighborhood of Lowell, and described by Mr. Clemens Herschel, M. Am. Soc. C* E. There the fitness of a material for puddling, or making a water-tight coating or layer, was ordinarily, tested by placing in a pail of water enough of it to render the water invisible. The pail was then turned upside down, and if the mixture dropped out it was rejected; if it remained in the pail it was considered satisfao tory for puddling. The importance of a proper selection of material for an em- bankment is so great that a number of opinions of leading Amer- ican engineers are quoted verbatim below. The author believes that these opinions are of great practical value, and to make them as useful as possible they are classed under the general heads of clay, gravel, and mixtures. CLAY. "A good illustration of the behavior of clay when used for pud- dling material in such proportions that its removal from the mass WATER-WORKS MANUAL. 25 by water very seriously disintegrates the whole mass, occurred on the Ridgewood reservoir of the Brooklyn Water-Works, built in 1857-60. The reservoir and embankment were built of material taken from the excavation, and well rolled and rammed. This material was the Long Island drift. Where the reservoir was ex- cavated below the natural surface of the ground the banks were dressed to a slope of 1| to 1, and a puddle facing 18 inches thick at right angles to the slope was put on, consisting of clay and grav- elly earth in about equal proportions. This material was wet and cut with spades. Above the natural surface the puddle wall was carried over the natural surface to the center of the embankment, and then carried up vertically in the center of the embankment. These banks were faced with a slope wall of split boulders about 12 inches thick, with the interstices well filled with pinners. When the reservoir was filled the water dissolved the clay out of the puddle, and the slope wall slid in some cases and settled back in others, and it was necessary to empty the reservoir and relay the whole of the wall in cement mortar. Since that time I have never attempted to use clay in puddling to which water could find access, and I think in general the less of such material there is used in puddling a wall the better the wall is/' J. J. R. Croes, M. Am. Soc. C. E. "The particles of clay are cohesive, and a vein of water ever so small which finds a passage under or through clay is continually wearing a larger opening. An embankment of clay is much tight- er at first (than one of gravel) but is always liable to breakage." William J. McAlpine, Past President Am. Soc. C. E. "Clay becomes slimy and sticky when wet, and yet it is difficult to mix it thoroughly with water. Hence voids are apt to occur in the body of the puddled mass. As the water leaves it it shrinks and cracks, and yet retains water in parts; so that it never prop- erly settles down and becomes compact, but is liable to be cut away if only a small stream of water passes through it, or if it is placed in water which is only gently agitated. I have no doubt that clay owes its reputation in this country to its mention in accounts of English work. There is a vast amount of what farmers call in- and-in-breeding' in the education and training of water-works en- gineers in the United States; so that when an error of this sort is once engrafted it is not easily eradicated. Clemens Herschel, M. Am. Soc. C. E. 26 WATER-WORKS MANUAL. "Some clays are apt to become saturated with water and under certain conditions to become fissured. They cannot, therefore, be used alone. Moreover, unless a clay is exceptionally tough, an aperture through it, however minute, is apt to become enlarged and finally to cause serious trouble. We find, however, that a number of dams of great height are reported from California as being built of clay. The designer of several of these dams stated that he had subjected a cubic foot of the clay to a hydraulic pres- sure much superior to that corresponding to the expected depth of water behind it and had been unable to force water through it; but these clays must be of very exceptional quality." A. Fteley, M. Am. Soc. C. E. "Fat or unctuous clays are mostly designated by writers on hydraulics as the only proper material of which to form an im- pervious, water-tight wall in the heart of an embankment, or the entire mound of a reservoir, as the case may be; and yet I am con- vinced that more failures of reservoir embankments and of high earth dams are due to the too free use of pure clay in puddled core walls, and to the almost entire dependence placed upon such walls, than to any other cause. The mistake too often made by engineers is that of supposing that only clay can be used for pud- dling. An embankment built entirely of clay is an unsafe one, even when puddled in the very best manner possible. It is easily attacked by muskrats and by other foes of a water-tight embank- ment/' E. F. Smith, M. Am. Soc. C. E. GRAVEL. "At many places the word gravel is understood to mean a mass of rounded stone of varying sizes. This sort of gravel occurs in very large deposits in many places and it is similar in the form of its constituent parts to the gravel of the seashore. The other sort of gravel is made up of stone not rounded, but rather of flat shape, and with many particles of very small size, but still not rounded. It is with this latter sort of gravel that tight puddle can be made without the admixture of clay. The gravel composed entirely of rounded pebbles of varying sizes will not alone make a tight bank, \)\it in many cases where clay occurs and only this sort of gravel can be found, an excellent puddle is made by a suitable mixture of the two. This is the case in the banks of the canals of the State of WATER-WORKS MANUAL. 27 Xew York, at many points in which a section of such puddled material is formed in the center of the bank, and which, when cut into afterwards, is found to be compact and impervious/ 7 John Bogart, M. Am. Soc. C. E. "By the term gravel is not meant a collection of clean, round, water- washed pebbles of nearly uniform size, but a combination of small stones, sand, and loam so proportioned that all interstices between the stones will be thoroughly rilled by finer materials. In certain proportions clay is valuable in such a mass, provided that it is so situated that water cannot get at it so as to wash out the clay, which consists of very fine particles capable of being washed away by the action of running water." J. J. R. Croes, M. Am. Soc. C. E. "The particles of fine gravel have no cohesion. A vein of water first washes out from the gravel the fine particles of sand, and the larger particles fall into the space, and these small stones first in- tercept the coarser sand and next the particles of loam which are drifted in by the current of water, and thus the whole mass puddles itself better than the engineer could do with his own hands. The vacuities produced below by this operation are indicated by the settlement at the top, where more gravel, etc., can be added as is found necessary. An embankment of gravel is comparatively safe and becomes tighter every day." William J, Me Alpine, Past President Am. Soc. C. E. "Gravel capable of being puddled will do anything that clay was ever used for in water-works practice, and will do it better. I have known cases where clay was brought at considerable expense to a bridge site to be filled into bags and used in coffer-dams, while good gravel, which would have done the work much better, abounded close at hand. Clay placed in such bags washes out and disappears, while gravel retains nearly its full dimensions in water." Clemens Herschel, M. Am. Soc. C. E. "Gravel suitable for use as a reservoir embankment may be de- fined as a material resulting from the disintegration of any of the harder rocks, with the admixture of water- washed pebbles and stones not larger than pigeon eggs nor smaller than the grains of coarse sand, with sufficient clay to bind the mass together when compressed. The presence of a suitable binder in the form of clay is the one important element in the make-up of gravel suit- able for puddling." E. F. Smith, M. Am. Soc. C. E. 28 WATER-WORKS MANUAL. MIXTURES. "The material in this section (Pittsburg, Pa.) contains more clay than does that found in Massachusetts, and when it is ex- cavated after a long dry spell, it is apt to come up in large lumps. If placed on the hanks in thin layers in its natural condition and thoroughly rolled so as to pulverize the lumps, the absorption of "water upon the filling of the reservoir causes the material to swell, and in my opinion, to make a tighter bank than when the material is put in wet." James H. Harlow, M. Am. Soc. C. E. "The writer is of the opinion that clay, on account of the fine- ness of its particles and of what is commonly called its binding qualities, must enter into the composition of the material used. That a very small proportion of it is sufficient is shown by the very excellent behavior of banks wholly formed of hardpan, in which the gravel and fine sand are cemented by the admixture of various proportions of clay." Alphonse Fteley, M. Am. Soc. C. E. "When engineers appreciate the fact that a homogeneous bank of gravel, compacted by a little clay, is better than a clay core with indifferent material on both sides of it, the number of failures will be comparatively few. Where true clays are used in proper pro- portions with other material they are fitted for the purpose of res- ervoir construction. In this I do not include those so-called clays which originate from sand that has been reduced to finely round- ed grains and which rather resemble quicksand." E. F. -Smith, M. Am. Soc. C. E. "The best natural puddle we have is hardpan, and if any of you have worked in hardpan you will have noticed that a great deal of gravel is encountered in it; it is also pretty hard to work, while pure clay can be easily worked. My experience has led me to work about 3 to 1 that is, I take pure clay, cut it up, and to every three barrows of it dumped down an embankment, or anything of that kind, I dump down a barrow of gravel and sand." Robert j Cartwright, M. Am. Soc. C. E. These quotations furnish such explicit information on the sub- ject of earths that little further comment is necessary. It is fre- quently desirable to form artificial mixtures of various materials in order to make certain portions of a dam particularly tight. The experienced engineer can generally decide upon the proper proportions without recourse to trial, but in case experiments are WATER-WORKS MANUAL. 29 necessary, the method recommended by Col. John T. Fanning, M. Am. Soc. C. E., is probably as expeditious and satisfactory as any. It consists in filling a water-tight box with the coarsest material available, and then pouring in water until all the voids are filled. The water is drawn off and measured, showing the amount of empty space in the box. Then this material is mixed with as much of the next finer available grade as it is possible to get into the box, and the voids measured with water again. When this process has been repeated down to the mixture with sand, the voids then left unfilled are to be filled with clay. Colonel Fanning states that if such an experiment is begun with 1 cubic yard of coarse gravel, and the mixing of the materials is well done, 0.28 yard of fine gravel, 0.08 yard of sand, and 0.03 yard of clay will make a mixture having voids of microscopic dimensions. As a standard for practical purposes he recommends 1 cubic yard of coarse gravel, 0.33 yard of fine gravel, 0.15 yard of sand, and 0.2 yard of clay. MASONRY CORE WALLS. There is probably as much controversial literature on the sub- ject of masonry core walls in the center of dams as on any subject pertaining to water-works construction, but it certainly is true that the general trend of opinion is in favor of their use in im- pounding dams. When properly built -they undoubtedly add to the safety of an embankment. Unfortunately they have some- times been poorly built and badly designed, and have naturally proved useless or worse. It has been stated by one eminent Amer- ican engineer that a core wall of one dam that failed was built of such insufficient dimensions that a horizontal section formed a convenient paper-weight, the thickness of the wall being 6 inches. On this subject the opinions of a number of prominent engineers are presented in the following quotations: "It seems to me that a core wall is always a good thing, and that in almost any ordinary case it is worth its cost. There are cases, of course, where its cost would be prohibitive, and there are cases where the material is of such an excellent nature that one is justified in getting along without it. But I will confess my- self to having a very strong preference for a core wall, both as a preventive against the workings of muskrats and of woodchucks and as a means of making the embankment tight; and also as a means of causing the destruction of the embankment to take place 30 WATER-WORKS MANUAL. gradually in case the water does penetrate it." John E. Freeman. M. Am. Soc. C. E. "As I said before, my idea of an ideal reservoir would be one of solid masonry,, and it can be made tight, and when it is once made tight it is there forever. But we can't always afford to build a re- servoir of solid masonry, and the next thing to it is to have a core wall of masonry,, which I should construct every time when I could get the material/' M. M. Tidd, M. Am. Soc. C. E. "In high reservoir embankments of the fin de siecle American pattern, sheet piling is replaced by a core wall of either concrete or masonry, founded upon the ledge or upon some other trustworthy substratum below the original meadow level, and extending up to the full- water level. This core is made some 4 or 5 feet thick at the top and at the bottom, tapering each way from top and bottom to a thickness of 7 or 8 feet at the original meadow level. I have heard these core walls criticised on theoretic grounds, but I know of no valid objection to them." Clemens Herschel, M. Am. Soc. C. E. "When it can be done within proper limits of economical con- struction, the writer prefers to secure water-tightness by means of an impervious wall built in or near the center of the embankment and continuously connected with the impervious bottom or extended downwards to a safe depth. There is no ques- tion that homogeneity in the mass of an embankment is very de- sirable; but the writer, with some experience of the difficulty of obtaining perfect work at all times, and of the trifling causes that can produce a leak through an earth embankment, prefers to use a masonry wall as a core. If a small defect exists in the core wall, only a limited amount of water can find its way out. I do not see that the presence of a masonry core wall weakens the structure in which it is built, for the tendency of the earth is to settle against the masonry. At any rate, I have failed to find, in all the cases of accidents which have come to my knowledge, any that were due to the presence of a core wall. The cause of the failure was invari- ably a defect in design or in construction." Alphonse Fteley, M. Am. Soc. C. E. "With regard to the construction of earthen dams, the speaker stated his belief that an impervious core wall could be obtained of other materials than masonry which would be just as good; it must be made of the best materials, however, and well placed. WATER-WORKS MANUAL. 31 Many miles of embankments and dams are now standing in the United States in which the center is a wall of puddled earth and clay, combined in suitable proportions and placed properly, and such walls are as impervious as any of masonry can be." Discus- sion by J. J. E. Croes in "Transactions" Am. Soc. C. E. "The speaker did not wish to go on record as being opposed to a masonry core, and he had under consideration at that moment a dam in which he was strongly inclined to put one. On the other hand, he regarded such a core as an extreme precaution for the sake of safety. If he had just the material wanted and was cer- tain that water would not rise to the top of the dam he was design- ing, he might be willing to build it without any masonry core, al- though it is 60 feet high." Discussion by John Bogart in "Trans- actions" Am. Soc. C. E. Where the masonry core wall is omitted, and the material of the dam is not exceptionally water-tight, it is necessary, in the class of dams under consideration, to make a core of puddled earth or a facing of that material on the upstream slope of the embankment. In most cases the former construction is preferable for the reason stated concisely by Mr. Fitzgerald, as follows: "For the same amount of money more puddle can be put in a vertical wall than on a slope of equal height. A puddle wall in the center of a bank is not exposed to the danger of slipping when the surface of the reservoir is suddenly drawn down. The water does not seem to work out of the puddle (when on the face of an embankment) quickly enough to drain the bank, and the result is a head, which caves the slope. Puddle in the center of an embankment is less exposed to frost, to drying out and to cracking than it is on the slope." The puddle earth ought to be of the best quality, free from lumps, without any stones larger than 2 inches, and prefer- ably still smaller, put on in layers not exceeding 6 inches in thick- ness, and cut and crosscut with spades every inch or so, until the layer is not more than 4-|- or 5 inches thick. Where the puddle covers such an area that grooved rollers can be employed to ad- vantage, it may be used in 4-inch layers and compacted in the manner to be described under the head of methods of construc- tion. There is no question that such a mass of puddle, if made of small, clean gravel with some clay, will be practically water-tight, but it cannot be relied upon to stop the burrowing of muskrat and woodchucks, which only masonry will prevent. 32 WATER-WORKS MANUAL. No matter what material is employed for a core wall, it must be carried down far enough and deep enough into the sides of the valley to prevent the passage of water under or around the dam through the undisturbed natural earth. This subject will be dis- cussed later. WATER IN EARTHWORKS. The tendency to use too much water in consolidating the layers of earth in an embankment is perfectly nat- ural from a contractor's point of view, because the liberal use of water will apparently make a very tight bank with the mini- mum expenditure of labor and time. With most of the materials used for such works, however, there is a strong probability of chinking of the bank as the surplus water dries out, if an excessive amount is used. Everyone has noticed how mud flats crack when exposed to the sun, and the action is the same, though on a much smaller scale, in an embankment kept too wet during con- struction. An experimental proof of this was furnished by some investigations made by Mr. FitzGerald in connection with his studies of evaporation. He filled eight large zinc-lined tanks with gravel, sand, earth, and mixtures of puddle and other ma- terials. In all cases where the filling was wet it was found to be impossible to keep the tanks full, no matter how much ramming was done. By ramming in dry materials, however, no trouble from shrinkage was experienced, and in every case the material brought the paint off from the zinc when it was removed. Some- times, as in the case of the reservoir of the new water-works at As- toria, Ore., the earth for a reservoir embankment is found in such a condition that no watering at all is necessary. With hardpan, however, some water must be used to make a compact bank. This material breaks up in lumps about 3 to 6 inches in size, which it is difficult to pulverize, especially if hard. If a little water is used to moisten the lumps, and the moist material is laid in courses not over 4 inches thick and well rolled, the bank can be made very tight. Dexter Brackett gives the cost of the watering and rolling of an embankment containing 80,000 cubic yards of hardpan as about 2 cents a cubic yard, the work being done thoroughly. It is particularly important to have the rolling and ramming of the material done under the supervision of a conscientious inspector, where but little watering is done, as the work is apt to be slighted. Alphonse Fteley advises the use of enough water "to give plas- WATER-WORKS MANUAL. 35 ticity to the earth and to moisten it to about the same degree as is observed in a deep excavation free from water." In the construction of the Clinton and Oak Eidge dams of the East Jersey Water- Works the gravel composing them was spread in thinner layers than usual, not over 4 inches thick, which were reduced to about 2 inches after rolling. J. Waldo Smith, M. Am. Soc. C. E., reports that at first the method of sprinkling and then rolling was followed. It was found that better work could be done and the material compacted more thoroughly by rolling first, then sprinkling and rolling a short time, and giving a final wetting just before the next layer was applied. The theory on which this procedure is based is that the air can be better forced out of the loose gravel, and the material made more compact while in a dry or naturally moist state, and that the subsequent addition of water still further settles and binds the whole mass. Whatever merit this theory may have, the practice it leads to, the use of a minimum quantity of water, agrees with the best usage at present. The following clause is taken from the specifications for Ee- servoir M of the Croton Water- Works of New York City: "Ample means shall be provided for watering the banks, and any portion of the embankment to which a layer is being applied shall be so wet, when required, that water will stand on the sur- face. The contractor shall furnish at his own cost the necessary steam or other power for forcing the water upon the bank if the engineer finds that other means of transportation and distribution of the water are not sufficient." The specifications for the dam for Eeservoir No. 5 of the Bos- ton Water- Works read much the same on the subject of watering. The wording of the clause in them is as follows: "Ample means shall be provided for watering the banks, and any portion of the embankment to which a layer is being applied shall be so wet, when required, that water will stand on the sur- face. The contractor shall furnish at his own cost the necessary steam-pumping plant and force main for forcing water into a tank situated on the side hill, at least 50 feet above the top of the dam when completed. From this tank a 3-inch distribution pipe, with gates and hose connections, will lead lengthwise over the dam to supply water wherever it may be needed. If the engineer ap- proves, some other method of equal efficiency for the furnishing of water may be substituted for the above plant." 34 WATER-WORKS MANUAL. These clauses refer to particular pieces of work very carefully studied by Messrs. Fteley and FitzGerald respectively. While they might be considered as indicating a preference for heavy watering, if they are examined carefully in connection with the previously mentioned statements of these engineers,, it will be ap- parent that they are intended mainly to secure provision by the contractor of ample watering facilities,, in case they should be needed. Like all other clauses from specifications which are printed in this series of articles, they are to be regarded as sug- gestions only, and not copied verbatim. It would be very foolish to insert the Boston clause in specifications for a small dam to be made of a naturally moist mixture of gravel, sand, and clay which does not require watering. CROSS-SECTION OF THE EMBANKMENT. The cross-section given the dam depends somewhat on its height, but the general form has been pretty well standardized by this time. American engineers have learned that it is unnecessary to have such flat slopes as are usually adopted abroad; 2 to 1 on the inner face, and the same rate, or 2J to 1 on the outer face, are the slopes generally employed. If the dam is quite high, a berm 5 or 6 feet wide should be made on the inner face a few feet below the low-water level, and a wider berm should be built on the outer face about one-third to one-half the distance from the top. The latter was probably first used in this country by Mr. FitzGerald, and provides a means of longitu- dinal drainage to protect the loam covering of the slope until the grass becomes well rooted on it. This berm must be well drained itself, however, or water will pass from it under the grass, under- mining and destroying, it. The height of the dam above the high-water level depends somewhat upon the size of the structure. If it is a high dam, the bank should rise above this level about 18 inches plus the depth of the frost in the locality where it is built. If the structure is low, this height is often made less and reliance placed on additional width at the top to prevent frost cracks from opening passages for the passage of water. Allowance must also be made for the height of waves in some cases. The width of the dam on top should not be less than 10 feet unless the structure is very small. All angles in the cross-section as first sketched out should be rounded off, as angles in earthwork are entirely theo- retical, except in rare cases. WATER-WORKS MANUAL. 35 STARTING THE CORE WALL. The portion of the dam liable to give the most trouble is the bottom of the core wall or the puddle core, since it has to be carried down to impervious material and may require diffi- cult trenching in water bearing strata. Quicksand is usually the worst material to deal with, and in case it is encountered the following notes may prove of value. They are abridged from a very valuable paper on the method in which a breach was re- paired in the dam of the storage reservoir of the Xew Bedford Water- Works. This paper was written for the American Society of Civil Engineers by the late William McAlpine. In the course of the repairs, a trench had to be made water- tight with sheet piling exposed in places to a head of more than 20 feet. For such a purpose Mr. McAlpine considered driven sheet piling worse than useless. His plan was to excavate the trench to the greatest depth practicable, and to place in the bottom a hori- zontal timber to which closely jointed planks were spiked. These planks were spiked to a similar timber at the top, and were cov- ered by a second course of jointed boards. A water-tight barrier can be made in this way, which it is very difficult, if not imprac- ticable, to obtain with driven plank. Another point to be con- sidered in sheeting a trench is that water will pass horizontally and vertically along a smooth surface for a great distance until it finds open joints through which it will pass freely. Water abhors angles, and by compelling it to make a sufficient number, its head can be destroyed entirely. The interposition of angles is often the only defense the engineer has against water, and the practice of placing instead of driving sheet piling enables many of these to be obtained. There are three rules to be observed in excavating quicksand. (1) the water must be removed promptly and thor- oughly, (2) the excavation must be made with the utmost dis- patch, (3) the material must not be disturbed after it begins to quake. Quicksand is a mixture of fine sand with such a propor- tion of clay or loam as enables the mass to retain water within itself; and when in this condition, after it has been trampled upon for a short time, it begins to quake, so that it may also be called quakesand. When it reaches this condition, if it is left quiet for a few hours, the heavier particles of sand and clay settle down and expel the water, and the mass becomes firm again. If, on the 36 WATER-WORKS MANUAL. other hand, it is further disturbed by the feet of the workmen, it becomes more and more fluid, additional material flows in from the sides, and no progress can be made in the excavation. When the engineer has such a work on hand he should provide ample pumping power, and in most cases he will find a power several times as great as he anticipated will often prove most economical in the end. The pumps should be capable of lifting sand as wel] as water, and those are best which are not liable to be clogged; this is of more consequence than that they should work with a good duty. Mr. Me Alpine found that in most cases sheet-piling protections around the pit to prevent the influx of sand are useless and often detrimental. If there is room to allow the excavation to take its natural slope and the three rules are observed, the sheet-piling protection will be found unnecessary. Quicksand in a dry state may be excavated nearly vertical. In the work at New Bedford the dimensions of the pit on top were about 50 feet width by 100 feet length. There were 30 la- borers employed. Six were kept constantly at work removing and casting side the sand from about and under the pump, to keep it far below the other pa~ts of the excavation. Twelve men were employed all the time opening small ditches radiating from the pump pit. Six men were employed in excavating the ridges left between the radiating ditches, and as long as the latter were kept open these ridges offered perfectly dry digging. The remaining men were employed in casting further back the earth which was thrown out by the six men last mentioned. The actual removal of the earth was measured by the work of only six men out of 30, but these six had perfectly dry earth to handle. There was con- siderable difficulty in compelling the men to follow the rules men- tioned previously. They were violating them constantly, al- though they had palpable evidence of the disastrous results due to their neglect. Work was begun early in the morning, and by noon the pit had been sunk to a depth of 12 feet at the lowest place. By this time it was apparent that the extreme capacity of the pump had been reached, and it became impossible to keep open the radiating ditches. Consequently the earth between them became suffused, and the whole of the lower portion was transformed from hard compact sand into a semi-fluid material quaking like jelly. Water WATER-WORKS MANUAL. 37 began to boil up in many places in the bottom, and it was evident that no further progress could be made at this time. The method of carrying on the work was then changed. It was very important that sheet piling should be placed at a much greater depth than the excavation had been carried, but Mr. Mc- Alpine believed that to drive the plank to the desired depth would have resulted in open joints at the bottom. It was therefore de- termined to lessen the number of such joints by making up the plank in panels of 4 feet width, with their joints matched and bat- tened with 1-inch boards. One of these panels was placed in the proper line of the sheet piling, and forced down by pressure to a depth of nearly 5 feet. A second panel was forced down in the same manner and with considerable trouble a tolerably close joint was made with the first and further secured by a plank driven over the joint. Successive panels were placed in this manner until the pit was covered by two rows of sheet piling placed 15 feet apart. There was considerable leakage through this piling, but by spend- ing about $200 in improving the sluice by which the water in the river was conducted past the pit, more than half the leakage was prevented. Under the new conditions the pump was found to have ample power to free the pit from water and enable the joints in the sheet piling to be calked so that the puddle could be put in. The full account of the work thus carried out will be found in Paper No. VII. of the "Transactions" of the American Society of Civil Engineers. It is one of the most helpful articles ever writ- ten for engineers engaged in hydraulic work, and is fortunately still in print. Another method of dealing with quicksand which has proved very satisfactory in many places consists in sinking driven wells along both sides of the trench. By pumping continually from these wells the subsurface water is kept at a low level in the vicin- ity of the construction. An illustrated description of the method followed in such a piece of work on the Metropolitan sewerage sys- tem of Boston was published in "The Engineering Kecord" of January 21, 1893. CHAPTER III. MINOR DETAILS OF RESERVOIRS. For the class of reservoirs used for small works such as are de- scribed in these articles, the construction of the pipes, gate-houses and waste weir is a very simple matter. But two pipes will be needed in the great majority of such reservoirs, one for the regu- lar supply and the other -for a waste pipe through which to draw off the impounded water. In carrying a pipe through an em- bankment subjected to water pressure, there are two points which must always be kept in mind. The first is that the exterior sur- face of a pipe or conduit of masonry offers excellent opportunities for leakage of water, and the second is that a pipe carried through an artificial bank is always exposed to breakage by the settlement of the earth. Mr. McAlpine's famous axiom, "Water abhors an angle," has already been mentioned, but it may be repeated again here as indi- cating the method of preventing the leakage of water along the pipes. The greatest care should be exercised in laying the pipes to have the earth tamped firmly against them, but even the most painstaking supervision in this respect will fail to prevent the passage of water along them. Hence cut-off walls of concrete or good masonry should always be built around the pipe to break the uniformity of surface and prevent the percolation of water. The late M. M. Tidd was accustomed to have cast on some of his pipes to be laid through an embankment, a collar or flange, 2 or 3 inches high and perhaps 2 inches wide, which was firmly bedded in ce- ment. In small reservoir dams a masonry cut-off placed around the pipe midway between the core wall and the foot of the inner slope, and another midway between the core wall and the foot of the outer slope, will be sufficient to stop any leakage, if the earth is tamped firmly about the pipe. These blocks of masonry should be made with great care, and if they stand out 18 to 24 inches from the pipe no harm will be done; they need not be more than 18 to 24 inches thick. WATER-WORKS MANUAL. 39 When a pipe is carried through an embankment it ought never to be supported on a series of masonry piers, one under each joint, as this practice is simply an urgent invitation to troubles of vari- ous sorts. In case the embankment settles, every length of pipe is subjected to a bending stress which tends to cause leaks. The moment a leak occurs, the water under pressure enters the earth about the pipe and loosens it, arid if the water does not sooner or later pass along the outside of the pipe to the face of the dam and cause a washout of part of the structure, it will be more a matter of good luck than good engineering. The fact that many pipes supported in this way have not broken does not make the practice a good one. The ideal manner of carrying a pipe through a dam is by resting it on some natural foundation, ledge, or dense hardpan, which is known to be absolutely unyielding, but if this cannot be done, a concrete or cement masonry wall, with several projecting cut-offs and a rough surface, ought to be built to support its entire length. The dimensions of such a foundation wall depend, of course, on the local conditions of each problem. The ideal method of leading pipes from a reservoir is to carry them through the natural foundations at one side of the embank- ment. This is generally quite expensive arid does not offer many advantages in the case of small reservoirs, although where the dams are high this plan is to be selected, if possible, for reasons which it is unnecessary to explain here. Too much emphasis cannot be laid on the importance, in any dam having pipes laid through it, of preventing the percolation of water along their exterior surface, and of preventing the break- age of the pipes by settlement. GATE-HOUSES. The gate-house of a small reservoir is a very simple struc- ture. In designing it, care should be taken that it is firmly founded, and that there is no chance for the pipes from it to become broken. The nature of the foundation is naturally governed by local conditions, but in case it must be on any other material than rock particular care must be paid to securing an ample bearing area, as the bottom of the gate-house and its con- nection with the dam are frequently weak points in an otherwise good design. There should be an opening in the wall at the level of the bottom of the gate chamber to enable the water to be drawn 40 WATER-WORKS MANUAL. off to the bottom of the reservoir, and it is a good plan to cover the bottom of the reservoir with riprap in front of the entrance, if this can be done without much expense. The other openings for water may be from 6 to 8 feet apart vertically. The size of the openings at each level may be determined by means of the fol- lowing formula: A = 0.3 Q, where A is the area in square inches and Q is the maximum quantity of water in cubic feet per second which the pipe line from the reservoir will carry. Manufacturers of valves now supply sluice gates for any open- ings which will be required for small gate-houses. They have bronze facing on the seats and gate faces, and can be had with a spigot on the back for building them into the wall or with flanges by which they may be bolted to the end of the pipe. The gates are raised in two ways, by means of a rising stem and by means of a non-rising stem. The rising stem is a rod firmly attached to the gate and threaded at the upper end. A hand wheel bearing against a large washer or plate is screwed on the end of the rod, and by turning the wheel the gate is manipulated. The non-ris- ing stem has a thread at the lower end and is keyed to the hand- wheel. The gate has a threaded hole through which the lower end of the rod passes, and is raised and lowered by turning the rod by means of the wheel. The rising stem is cheaper and pref- erable in most cases. The face of the sluice opening on the out- side of the gate-house should be finished off smoothly so that it may be closed with a wooden plug wrapped with canvas in case of an emergency. The gate chamber is generally built of rubble or brick masonry, but sometimes other materials have been used. Now that vitri- fied brick are so cheap the best lining in many cases would be made of this material, but good hard-burned brick will answer. In fact no lining at all will be needed with the rubble masonry of some parts of the country, as a really good Portland cement finish will answer all purposes. This applies to small work only. In the design of the gate-house particular care should be paid to se- curing a structure which will not be exposed to damage by the ice. During the winter and early spring there is always a possibility that the water will rise, lifting the ice and loosening that portion between the gate-house and the sloping back of the dam, so as to bring a strong pressun against the former. In very cold climates there is also dange 01 the ice lifting the masonry if the latter is WATER-WORKS MANUAL. 41 very light. For these reasons a gate-house is generally a more massive structure than a statical analysis of the strains upon it would call for. The arrangement of the effluent pipes from a small reservoir admits of little variety. Two different plans are shown in Figures 2 and 3, and modifications of these will probably answer all pur- poses. The first plan, shown in Figure 2, will answer for the i*- 16"-* Waste Pipe, FIGURE 3. FIGURE 4. smallest reservoirs. The waste and main pipes end in elbows, with the openings flush with the bottom of the chamber, and have no valves at the inlet end. The cut is a section through one of the pipes. In case it is desired to close the end of either pipe, it can be done very quickly by means of an iron plug wrapped with canvas, a little hemp being placed as a padding between the can- 42 WATER-WORKS MANUAL. vas and iron. The. tightness of such a plug is surprising, and it can be placed in position by means of a rope or chain when the well is full of water. The suction of the water entering the pipe will seat the plug firmly. Above the mouths of the pipes is a weighted wooden frame having a screen of No. 10 copper wire making quarter-inch meshes, or a sheet of copper perforated with quarter-inch holes close together. The copper sheet is cleaned more easily than the screen. The frame is arranged so that it can be lifted to the surface readily. When such a system as this is employed a small valve chamber should be built at the outer toe of the embankment and covered with a strong wooden or masonry box, by which the valves may be reached. The cover to the box should be provided with a good lock to prevent any tampering with the valves. The waste pipe should be carried far enough be- yond the gate-house to reach a convenient locality for discharging readily the water passing through it. The end of the pipe should be protected in many cases by a cement masonry wall resting on a good foundation, and the ground immediately in front of the end of the pipe should be paved with small field stone to prevent the washing away of the earth. Such an arrangement as this is prob- ably as cheap as anything reliable that can be designed. The ex- tra cement masonry filling required to form a level surface at the mouth of the elbow and for the small valve chamber will be less expensive in most cases than the standards and fittings necessary to manipulate the valves were they placed in the main well in- stead of the small gate chamber. Such a system is to be selected foA the smallest works only, where it is necessary to keep the first cost down to the minimum amount. The greatest depth of water for which the plan is suited is not much over 10 feet. A somewhat more elaborate gate-house is shown in Figure 3. where the valve chamber ; s 4 feet square, inside dimensions, and the walls are 16 inches thick. The two pipes, assumed to be 8 inches in diameter, are each provided with a single gate valve. The waste pipe runs directly from the outside face of the wall and has no connection with the valve chamber. The main pipe ends in a small screening well about 20 inches square and 1 foot deep. This is covered by a frame having a screen of wire or perforated plate. This frame can be pulled to the surface whenever it is necessary to clean it, and can be placed in position again without much trouble with the aid of a pole kept in the valve chamber* WATER-WORKS MANUAL. 43 With this plan it is proposed to draw water from the reservoir at different heights through sluice gates arranged in the manner shown in Figure 4. The advantage of this method of construction over the first is due to the complete control of the water at the place where it leaves the reservoir instead of below the dam. The screen is hori- zontal and therefore more liable to become clogged than if it were placed in an upright position, but on the other hand the cost of such screening apparatus is very small as compared with that of the screens shown in Figure 4. The valves have bell ends and are calked to the pipe in the usual manner for such valves. In the cuts the vertical cross-section is taken on the line C D and the plan on the line A B. The gate-house shown in Figure 4 is representative of the best class of such structures for small works. It was built recently at Ipswich, Mass., from plans prepared by Freeman C. Coffin, M. Am. Soc. C. E. The depth of water in this reservoir above the concrete foundation is about 1 8 feet, and two sluice gates are pro- vided by which the supply can be drawn off of the bottom of the reservoir or from about mid-depth. The chamber is divided into two portions, each 8 feet by 3 feet 2 inches in plan, by the double set of screens and the grooved masonry walls in which they slide up and down. These screens have wooden frames measuring about 4 1 x 4 feet, four frames being used for each vertical set. The advantage of the duplicate screens is that when one set is re- moved for cleaning, the second set is still in place to prevent the .entrance of large solids into the main pipe. The discharge pipe, it will be noticed, has no communication with the gate chamber in which its valve is located. The flow of water into the main pipe is controlled by a sluice gate with a flange connection, by which it is bolted to the end of the pipe. The top of the gate chamber is provided with a brick arch carrying the floor, which has a trap door through which the screens can be raised or low- ered. The gangway to the gate-house from the embankment is carried by two 6-inch 16-pound I beams, and has a light railing made of 1-inch and 1^-inch gas pipe. The bank end of the gang- way is supported by two 6-inch vertical pipes resting on blocks of concrete imbedded in the dam. An 8-inch channel iron is laid over the top of the two pipes, and the beams, channel, and pipes are united by a few rivets and pieces of angle iron. 44 WATER-WORKS MANUAL. WASTE WEIRS. The safety of an earthen dam depends in a great measure on the proper proportioning and construction of the waste weir by which the surplus water in the reservoir may be discharged. The first step in designing such a work is to ascer- tain the probable maximum run-off of the watershed above the dam and prepare the plans so that this entire volume may be dis- charged without allowing the high-water level in the reservoir to rise above the elevation assumed in designing the embankment. An examination of the site of the reservoir will often furnish in- dications of the great floods in the stream to be impounded, and valuable information can generally be secured from the residents in the vicinity. It is particularly important to remember that the discharge per square mile of small watersheds is liable to be excessive when compared with that of larger areas. Capt. James L. Lusk, of the Corps of Engineers, United States Army, recently made a valuable compilation of the freshet discharges from water- sheds of moderate area; this is not easily accessible, so the most important figures are reproduced in Table No. 4. Table A~o. 4. Freshet Discharges in Cubic Feet per Second per Square Mile from Small Watersheds. Dis- Watershed. Year. Area. charge. South Branch, N. Y 1869 7.8 73.92 Woodhull reservoir, N. Y 1869 9.4 77.76 Stony Brook, Mass 1886 12.7 121.03 West Branch, Croton River, N. Y 1874 20.4 54.43 Watuppa Lake, Mass 1875 28.5 72.00 South Fork Creek, Pa 1889 48.6 215.11 Flat River, R. 1 1843 61.0 120.85 Sudbury River, Mass 1886 75.2 44.26 Rock Creek, D. C 1856 77.1 126.40 Additional information bearing on the subject can be gathered from statistics of rainfall in the vicinity, if such have been kept; it is surprising how many amateur meteorologists there are throughout the country, and a diligent inquiry will generally se- cure some valuable information on heavy storms. Such figures, however, must be regarded as guides rather than as limits, for the waste weir must be large enough to discharge a greater quantity than has ever been measured, or the probabilities are that sooner or later the dam will be overtopped. In reporting on this matter to the Boston Water Board, the late James B. Francis, whose knowledge of rainfall and stream flow was remarkable, advised WATER-WORKS MANUAL. 45 proportioning the arrangements for the discharge of surplus water so that their capacity would he equivalent to a rainfall of 6 inches in depth in 24 hours over the whole watershed. This is several times the largest measured rainfall. Mr. Fteley made the same recommendation in a report to the Aqueduct Commissioners of Xew York City. His report reads as follows: "As to the capacity of the overflow, it is necessary to depart from precedents on account of the extent of the watershed and the comparatively heavy rainfalls that occasionally occur in the Croton basin. Judging from the possibilities of rain or thaw in this and neighboring watersheds, the flowing capacity- of the over- flow should not be less than equivalent to the flow in 24 hours of a volume of water represented by a uniform thickness of 6 inches over the whole watershed. "It is true that no such flow is on record, and the actual flow may never, it is hoped, come to that figure, but a combination of adverse circumstances, such as an exceptionally heavy rainfall oc- curring at a time when the ground is covered with snow, can bring about such a condition of things, and it is wise to be prepared for it. It can be so much more readily done that an increase in the length of the overflow can be obtained at a comparatively small cost. "The writer having had occasion to design the overflow of sev- eral dams on an equivalent basis, may be allowed to state that, on the occurrence of a freshet which produced a flow somewhat less than one-half of the quantity just mentioned, he could not but feel in accordance with the sentiment of the people living lower down in the valley, that the channels of discharge were none too large." Many attempts have been made to formulate a mathematical expression for the discharge from a watershed, but no one expres- sion has yet been obtained which will give more than approximate indications. India has been particularly prolific in producing these formulas, and Mr. H. M. Wilson, M. Am. Soc. C. E., states the following are two of those most used in that country: Ryves' formula, D c tf ^L- Dickens' formula, D = c \/ A* where A is the area of the catchment basin in square miles; c is a coefficient depending for its value upon rainfall, slope, soil, and 46 WATER-WORKS MANUAL. other local conditions; and D is the discharge in cubic feet per second. In the Dickens formula, the value of c for places where the maximum rainfall in 24 hours is 3.5 to 4 inches varies from 200 for flat country to 300 for hill country. Where the maximum rainfalls is 6 inches the coefficient ranges from 300 to 350. For the Ryves formula, the coefficient varies between 400 and 500, and for very hilly areas, where the maximum rainfall is high, it may reach as high as 650. Col. J. T. Fanning, M. Am. Soc. C. E., has given the following formula as an approximate expression of the mean maximum discharge from a number of American water- sheds: D = 200 y~T* Although such formulas have been employed to a considerable extent in the past, they are really of little value except as checks on estimates of flood discharge obtained in other more reliable ways, and in designing waste weirs, if the estimates exceed the re- sults given by the formulas they should certainly be used. Mr. Desmond FitzGerakl makes this very important statement con- cerning iS r ew England watersheds in his able paper on "Rainfall, Flow of Streams and Storage/' previously referred to: "The water- works engineer who is constantly designing waste weirs, dams, reservoirs, etc., may find it convenient to bear in mind that I square mile of land surface yields approximately 1.5 cubic feet per second throughout the year, and that the maximum freshet flow may be a hundred times this amount, or 150 cubic feet." The location of the spillway through which the waste water flows from the reservoir must of course be determined by local conditions, but prudence demands that wherever possible it should be around rather than over the dam, eyen where the cost of this plan is somewhat greater. No matter where it is located, its di- mensions should be selected only after careful consideration. It is now the opinion of a large number of engineers that water- works reservoirs should not be provided with the movable flash- | boards on the waste weirs, which- were quite common in small works until recently. These engineers claim that it is safer in the end and possibly as economical, in view of the employee's time re- quired to watch the flashboards, to make the sill of the waste weir the maximum level of impounded water in the reservoir and never attempt to raise the water higher. This provision calls for long rather than deep waste weirs. WATER-WORKS MANUAL. 47 An old and frequently quoted rule for ascertaining the approxi- mate length of a waste weir is to make it 3 feet long for each 100 acres in the catchment area. Just who originated this rule the writer has never been able to ascertain, but it leans toward safety, and for areas exceeding 3 square miles gives an excessive length. For smaller areas it seems to furnish a useful approximate method of calculation, while for larger areas Mr. E. Sherman Gould's for- mula is more in accordance with practice. The latter expression is: L = 20 yA where L is the length of the weir in feet and A is the area of the catchment basin in square miles. To find the depth of water in feet, H, on the weir when the maximum flood discharge Q is pass- ing over it, it is necessary to employ the following formula: H = 0.459^g' -H L. This height added to the elevation of the sill of the weir gives the maximum water level in the reservoir, and the dam must rise at least 3 or 4 feet above this in order to prevent it being overtop- ped by waves. Mr. Gould has suggested that the depth of water on the sill, when a flood volume of 150 cubic feet per second per mile is passing over a weir of length of ZQy'A may be ex- pressed with sufficient accuracy for most purposes by the simple expression: H= 1.77 y A. It must be distinctly understod that these formulas and rules are only fair approximations, and that after the weir is designed and the shape of the sill and ends determined, a more exact com- putation, using the proper weir formula for the conditions, will probably indicate a variation of perhaps as much as 10 per cent, from the first calculations. It may even be necessary to alter the length of the weir slightly to give it the requisite capacity. The latest editions of Trautwine's Pocket-Book, as well as all books on hydraulics, give such full information on weir formulas that it is unnecessary to go into the subject in this place. The waste weir of an earthen dam is really a different kind of a dam connecting the two portions of the embankment, and it is therefore very important that the surfaces of contact where the different materials join should be so arranged as to prevent the leakage of water. In this case, again, the maxim, "water abhors 48 WATER-WORKS MANUAL. an angle," is the golden rule of success. The earth bank on each side of the weir must be held by wing walls of some form, and these walls must be carried down to good foundations. There is one not uncommon exception to this rule, which is made when the dam has to be founded on sandy soil, such as underlies all the reservoirs of the Brooklyn water-works. The method of treat- ment in such cases was introduced many years ago by the late James P. Kirkwood, and has been followed with success in many subsequent structures, one of the latest being the new dam of the Syracuse water-works at Skaneateles Lake. It may be best de- scribed by abridging Mr. Kirkwood's account of the construction Water Level Scale 10' 20' Water Level. FIGURE 5. WASTE- WEIR ON SAND FOUNDATION. of the weir of the Jamaica reservoir dam, an earthen embankment with a puddle center wall. The bottom of the reservoir is fine sand and gravel of the same character as the material of the surrounding plain, and the earthen dam has a puddle wall in the center made of fine gravel and sand. The general form of the waste weir, which has a clear length of 21 feet, is shown in Figure 5. The masonry is granite laid in hydraulic cement mortar, and rests on a timber platform arranged as shown in the illustration. In order to prevent an excessive leakage of water under the plat- WATER-WORKS MANUAL. 49 form, a row of sheet pilling was driven on its upper side and ex- tended a short distance into the bank at either end of the ma- sonry. The specifications required this piling to be driven to a depth of at least 12 feet, but this clause was not carried out. The result was that the platform was undermined by water and had to be rebuilt with sheet piling in conformity with the requirements of the engineer. Two openings were left in the masonry, as shown in the illustration, to allow free passage of the water of the brook during the construction of the works. These openings were afterward closed and the upper face of the overfall, toward the reservoir, covered with earth. It will be noticed that the masonry of one wall has two buttresses. These were provided to break the surface and prevent leakage along the back of the wall, and as a further precaution the puddle wall was increased in width as it approached the masonry, until it covered the entire space between the buttresses. The masonry of the other wing wall was continued to form a sluiceway, which is not shown in the cut. The pavement on the apron was laid in courses with cement mortar, and was continued down-stream by a mass of rubble to protect the sheet piling at that place from eddies. Such a method of construction would, of course, be dangerous where it was not certain that the timber platform would remain below the permanent level of the ground water. The cross-section of the masonry of the weir is typical of the form generally given to such structures which are not much more than 10 feet high. The section is calculated by the same methods as a masonry dam. The down-stream face is usually given a slight batter, 2 inches to the foot. The design of the top is really the part calling for the most judgment, since its width must be decided upon after studying the probable character of the debris that will pass over it. If it is certain that no logs or other heavy masses will ever be driven against it, then its slope may be slight, say 2 inches to the foot, and its width kept down. But if logs, and broken ice are to pound against it during every spring freshet,, then the slope may be made a little greater, so that the logs and ice will be more likely to strike on it during floods than on the face of the dam itself. The width in this case must be ample to insure perfect security, and the stones of the sill should be large and heavy, cut to shape accurately and well bound together. Just what width to select for a given case cannot be expressed in a rule, 50 WATER-WORKS MANUAL. but' must be determined by judgment aided by established prece- dent. The slope of the upstream face is made so as to give a dam of the requisite degree of security. If the weir is more than about 10 feet high its down-stream face should be stepped so as to break the fall of the water and diminish its erosive action on the bottom, as will be explained more fully in the chapter on masonry dams. In any case particular attention should be paid to protecting the surface on which the water strikes. This is frequently done by a pavement of stones about the size of granite paving blocks, laid in 1-44.00 Scale. 0' I' 2' 3' 4' 5' G' 7 ~\ +44. 25 Profile ot Bridge. Cross -Sect ion below Planks. 6. WASTE WEIR AT NATICK, MASS. cement mortar and resting on a well-consolidated bed of gravel or field stone, but many, other methods of construction have been used. , A waste weir used on a spillway at one side of a small earth dam at Natick, Mass., is shown in Figure 6. It was designed by Mr. Desmond FitzGerald, and may be taken as a model for small work where the spillway is around and not over the dam. Timber weirs do not possess the durability of well-built ma- sonry structures, yet they have many good features. When con- WATER-WORKS MANUAL. 51 structed properly they last many years, and such repairs as a good timber weir requires can generally be made expeditiously and at a very small expense. The form given such weirs varies greatly, just as the form and method of construction of timber dams seem to follow no fixed types. Col. J. T. Fanning illustrates quite an elaborate weir of this sort (see Figure 7) in his "Treatise on Hy- draulic Engineering/' The timbers in it are stripped of bark and dressed on two sides to a thickness of 12 inches. The purpose of the sheet piling is to check the percolation of water under the dam. The timbers laid on the sills are 5 feet apart, and on these the frame is built up as shown. The sticks are united by J-inch FIGURE 7. A TIMBER WEIR. round iron drift bolts long enough to pass through two timbers and a half way into the third. As the frame is built up, the open- ings must be packed tight with stone and gravel of such propor- tions that the work will be watertight, a matter requiring care and thoroughness to be successful. The benches and crest should be made of carefully jointed timbers laid close, and the upper and lower faces covered with tightly jointed plank. If such a weir has to be founded on rock, the bottom courses of timber should be bolted firmly to the rock. Whether the weir be masonry or timber, a bank of gravel should be placed against its up-stream face. CHAPTER IV. TIMBER DAMS. The timber dam is often regarded as a cheap makeshift, good enough for temporary use, but never to be mentioned to clients as a structure of any engineering importance and never to be recom- mended except for situations where other engineers will probably never see it and thus have a chance to laugh at its designer. Re- cently, however, engineers of high standing have designed such dams for situations where permanence and durability were neces- sary, and the feeling is growing that timber dams of some of the types which have stood for many years on New England mill sites and along the canals of the Eastern States are deserving of more attention. Whether or not such a structure should be built de- pends largely on its cost compared with earth and masonry dams, and on the nature of the work that will be necessary to replace it when complete reconstruction becomes necessary. It will some- times be found that a small dam will impound a sufficiently large supply to enable a community to have all the water it wants for a period of 15 to 20 years, when the normal growth will require a daily supply that can only be obtained by the construction of a reservoir in another locality. In case the construction of this large reservoir should be more costly per million gallons stored than that of the smaller reservoir, then it may be good practice to build the latter, and in such a case a timber dam may afford a safe and cheap means of accomplishing this end. In a very gen- eral way it may be estimated that a large well-built timber dam will cost about one-half or three-fifths as much as a masonry dam of the same height and will last half a century with but very little outlay for repairs, while the cost may be reduced very much with- out impairing the safety of the structure by using less care in the construction. Small timber dams may often be constructed at a remarkably small cost: It must not be forgotten, however, that timber must be continually below the surface of the water if it is to remain in sound condition, and on this account timber dams WATER-WORKS MANUAL. 53 are more suitable for diversion weirs for directing part of the water of a river into a canal than they are for storage reservoirs. BRUSH DAMS. The brush and rock dam of the Western States is merely a makeshift, but in case it is necessary to build a dam not over 6 feet high across a stream having a quicksand foundation this type of a structure may serve a very useful temporary purpose. Mr. W. W. Follett, M. Am. Soc. C. E., who has an extensive acquaint- ance with irrigation works, recommends tying the brush, prefer- ably willow, into fascines 6 to 8 inches in diameter. The back of the dam may be quite steep, but the front should slope very gradu- ally in order that the water may leave the brush almost horizon- tally. A more elaborate affair is sometimes constructed by driv- ing piles and building brush and rockwdrk around them, the whole being provided with a timber overfall, or upper covering, and apron. In the streams where such structures are employed, the brush and rock are usually to be obtained near at hand, and when placed in position are soon silted into a fairly tight dam by the fine sand and sediment in suspension in the water. If a rapid rise carries the whole work downstream the loss is slight and can be quickly