Variation of the Longitudinal Dispersion Coefficient in the Delaware River Estuary as a Function of Freshwater Inflow

Abstract

Three solutions of the one‐dimensional steady state diffusion equation for a conservative substance (ocean salinity) have been derived for an estuary whose cross‐sectional area increases linearly in the seaward direction. One solution results from the assumption that freshwater enters the estuary only at the upstream end. The two other solutions result from the assumption that freshwater inflow increases as a function of distance along the estuary. The latter two solutions are separated by different upstream boundary conditions. The three solutions have been tested with U.S. Geological Survey water quality monitor data from a reach of the Delaware estuary. The tests indicate that the longitudinal dispersion coefficient, which is assumed to be spatially constant at any particular time, increases with freshwater inflow from about 140 to 200 m2/sec as the freshwater inflow at Trenton, New Jersey, increases from 2000 to 6000 cfs (60 to 180 m3/sec).