Port Phillip Bay is a large embayment in south-eastern Australia. It receives anthropogenic inputs from surrounding catchments, including treated wastewater and urban stormwater runoff. Yet, the long-term condition of the bay is resilient and continues to sustain important social and economic activities, such as swimming, boating, fishing, transport and shipping.
Melbourne Water have developed catchment and hydrodynamic models that incorporate water quality to better understand the complex dynamics of Port Phillip Bay. The regional-scale Source model estimates the daily delivery of pollutants and flow from the catchments. It provides a key input to the 3D hydrodynamic and nutrient-phytoplankton-zooplankton model for the bay, known as Bubbles. The Bubbles model is unique because planktonic transformations are calculated in packages that move through time and space using currents in the hydrodynamic model rather than a fixed grid. This method gives better positional accuracy and higher resolution of outputs.
Integrating these catchment-bay models improves forecasting of impacts from large-scale changes in catchment runoff quality and/or quantity. Better insights on nutrient cycling and plankton dynamics enhances knowledge of these critical in-bay processes for maintaining bay health. These coupled models will be a vital resource for tackling challenges from climate change and future population growth.