Coupled hydrodynamic and transport models of Port Phillip Bay, a semi-enclosed bay in south-eastern Australia

Coupled hydrodynamic and transport models of Port Phillip Bay were developed as part of the Port Phillip Bay Environmental Study. Model coupling was achieved via a particle tracking method, giving great flexibility in both geometry and time step for the transport model. This technique allowed ecological (water quality) modules to be included efficiently, so that long-term management scenarios could be adequately addressed. Validation of the hydrodynamic model was done primarily against observed sealevel and current meter data. For the transport model, comparisons were made with data on salinity in the bay observed over five years. Despite some disagreement between the hydrodynamic model and observations of longer-term (non-tidal) currents, the transport model provided good simulations of salinity throughout the bay. Transport-model flushing time for the bay was about 270 days (similar to estimates obtained from salinity and radionuclide measurements), varying with model geometry and with position inside the bay. As well as providing physical forcing for ecological simulations (described elsewhere in this issue), the models identified a systematic bias in the known freshwater budget for the bay.