3D Model of Estuarine Circulation and Water Quality Induced by Surface Discharges

Abstract

A three-dimensional numerical model system was developed to predict circulation and water quality induced by surface discharges in estuarine and coastal waters. The model system consists of hydrodynamic, pollutant-transport, and turbulence models. The model employs a new vertical γ-coordinate system, using an algebraic transformation within the well-known σ-coordinate transformation. Grids can be concentrated near the surface and bottom boundaries with a concentration factor proportional to the local water depth. Conservation equations are solved by finite-difference techniques. A semiimplicit algorithm is used for the vertically averaged exterior flow, and a vertically implicit procedure for the interior flow as well as salinity, pollutant constituents, and turbulent kinetic energy and dissipation. The hydrodynamic model was tested against analytical solutions for tidal forcing and density-induced flow in an open channel, and wind-forced flow in a closed basin. The vertical γ-grid system was tested for wind- and density-induced-flow cases. The constituent transport model was tested for salinity intrusion in a uniform open channel. Simulations show good agreement with analytical solutions. The fully coupled model was tested against laboratory experiments for a surface freshwater discharged into a saline quiescent receiving water in a constant depth basin. The predicted velocity and shearing depth, with the eddy viscosity obtained from the turbulence model, compare well with observations.