A Model of Dynamics in the Lower Potomac River Estuary

A simple two-dimensional numerical model has been developed to represent the observed vertical structure of tidal and nontidal currents and tidal elevations along a reach of the lower Potomac River Estuary. The model is based on a linearized longitudinal momentum equation and a laterally averaged continuity equation. It incorporates the effects of a naturally varying channel cross-section through the continuity equation, and a seaward increase in density through the pressure gradient term in the momentum equation. The observed distribution of density in the reach is used to evaluate the horizontal pressure gradient relative to the water surface. The model utilizes a coefficient of vertical eddy viscosity which varies both vertically and longitudinally. With but two adjustable parameters associated with the eddy viscosity, good agreement is obtained between the computed and observed tidal and nontidal currents.