Hydrodynamic and transport models of Western Port, Victoria

Abstract

As a part of the Westernport Bay Environmental Study several numerical models of water quality and chemical transports have been developed. The Hydrodynamic Model includes the effects of wind stress, bed shear stress, Coriolis force, local and advective accelerations, and water surface slope. The model consists of a finite-difference scheme for solving the depth-averaged hydrodynamic equations in two dimensions. The output consists of arrays of tide height and two horizontal velocity components at each grid point and computational time step. The Pollutant Transport Model uses Elder's equations for longitudinal and transverse dispersion in an open channel. The trajectories of computational particles of water carrying pollutants and other materials are calculated at successive times as they are moved by the currents and as they are spread by the action of turbulence and non-uniformities in the velocity profile. This model treats the non-reactive or conservative materials in the water. The Chemical Kinetics and Interaction Model, which is run jointly with the Pollutant Transport Model, simulates the behaviour of non-conservative and interacting materials. Quantities modelled are heat content, organic carbon, dissolved oxygen, nitrogen in its various forms, suspended sediment discharges, coliform bacteria, and any exponentially decaying materials. The model computes concentrations of materials at the various grid points and time steps. The Hydrodynamic and Pollutant Transport Models have been run for an average tide (the M2 component) and a sequence of spring tides. Computed half-tidal fluxes across seven sections dividing the major segments of the bay compared favourably with measured values. A detailed comparison of depth-averaged velocities was also made at the seven sections. These models have been used to predict the patterns of water movement in the bay and to interpret observations made in some of the other studies.