Comparison of two 2-dimensional, laterally averaged hydrodynamic model applications to the Swan River Estuary

Two laterally averaged, two-dimensional models; TISAT and CE-QUAL-W2, have been applied to the Swan River Estuary. Both models use a finite difference scheme. The time step in the TISAT model is restricted by Courant–Friedrichs–Lewy (CFL) criterion, but this limitation is overcome in CE-QUAL-W2 by using a semi-implicit numerical scheme. In CE-QUAL-W2 numerical diffusion has been reduced relative to TISAT by implementing a third-order QUICKEST horizontal/vertical transport scheme and time-weighted, implicit vertical advection. Predictions of salinity distributions from both models are compared with field observations for the Swan River Estuary in 1994. Both models simulated measured data reasonably well when there were accurate input data. During the period of intense stratification, predictions from CE-QUAL-W2 compared better to measured data than those from TISAT due to the improved transport scheme used in CE-QUAL-W2. Both models gave poor comparisons with measured data at the start of winter, when we hypothesised that the volumetric contribution of ungauged urban drains was particularly significant. In general, CE-QUAL-W2 offers significant advantages over TISAT in simulations of seasonal density stratification in the Swan River Estuary, particularly when there is intense stratification.