Simulating the Delaware Coastal Current

This research seeks to increase understanding of processes influencing freshwater distribution on the continental shelf. The overarching goal is to simulate the Delaware Coastal Current (DCC) under high discharge conditions. This large scale buoyant outflow is fueled by freshwater inputs into the Delaware Bay.; Model results are compared to tidal information, estuarine salinity data, and DCC observations. Simulation efforts focus on spring 1993 because of the wealth of data available for comparison. High river discharge during this year produced a strong buoyant outflow.; The simulation is used to investigate how river discharge, tides, and winds interact to determine the nature of the Delaware buoyant outflow. Several scales are used to characterize dynamics. These scales can be applied to other coastal buoyant outflows.; Scales for plume thickness, width, and velocity (u_dis) have been explicitly linked to river discharge forcing. The DCC velocity jet is several kilometers offshore due to bottom trapping. A trapping time scale (t_trap) for buoyant outflows has been developed. The DCC has a short enough t_trap (a few days) to become bottom trapped nearly everywhere.; Tidal effects are strongest near the mouth; current amplitude (u _tide) decreases with squared radial distance from the mouth. A coastal current is tidally reversed where the tidal displacement index (T_d = u_tide/u_dis) is above one. Tides reverse the DCC within 35 km from the mouth. Tides also modulate plume width and stratification.; Downwelling-favorable winds accelerate downshelf flow, narrow the plume, and decrease stratification. Upwelling-favorable winds counter buoyancy-driven flow, spread the plume offshore, and mix buoyant waters. A time scale (t_tilt) has been derived to estimate the time necessary for winds to appreciably modify width. The DCC t_tilt is less than a day for typical wind speeds. The wind strength index (W_s) compares wind-driven alongshelf flow to u_dis. When |W_s| exceeds one, buoyancy dominates and flow is downshelf. During the spring, the DCC is buoyancy-driven most of the time. Wind events, however, can dominate (|W _s| > 1) even during peak discharge conditions. When upwelling winds dominate, wind-driven reversals occur. These events constitute an important mechanism for transporting freshwater upshelf. Mixing during these events erases the buoyant outflow.