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