The Gulf of Mexico experiences a range of energetic flows throughout its complex bathymetry and topography. Tides in the Gulf of Mexico are modestly energetic processes whereas hurricane surge and wave environments are enormously energetic. High river discharges in the Mississippi River pose flooding risks to regions in both the Mississippi and Atchafalaya river basins. Hurricanes in Southeastern Louisiana develop significant surges along the lower Mississippi River levees. Storms with strong sustained easterly winds push water into shallow Breton Sound, overtop the river's east bank south of Pointe a la Hache, penetrate into the river, and are confined by levees on the west bank.  This dissertation applies the high-resolution, unstructured-mesh, wave-current SWAN+ADCIRC model to examine river flows and water levels in the Mississippi and Atchafalaya rivers. Model development extends to surge characteristics during hurricane events within the Mississippi River. A river velocity regime-based variation in bottom friction and a temporally-varying riverine flux-driven radiation boundary condition are applied. The coupled modeling system is validated for riverine stages and flow distributions, tides and historical hurricanes Katrina (2005), Gustav (2008) and Ike (2008). This dissertation investigates the effects of topographical details and bottom friction formulations on tidal and hurricane surge processes at the basin, shelf, wetland, and coastal channel scales within the Gulf of Mexico. The unstructured coupled wind-wave and circulation modeling system, SWAN+ADCIRC, is implemented to generate modeled tidal harmonic constituents, and hurricane wave and surge characteristics for a Hurricane Ike wind forcing. Low-lying near-shore coastal features are shown to impact tidal flows in the Gulf region, while use of a lower limit on bottom friction is shown to directly impact hurricane surge water levels and currents.