Modelling the biogeochemical drivers of water quality degradation in the Swan-Canning estuary

The Swan-Canning estuary in Western Australia has been the focus of intense management efforts for the past several decades since it has undergone major changes due to the impacts of excessive nutrient and pollutant loads... [ view full abstract ]

The Swan-Canning estuary in Western Australia has been the focus of intense management efforts for the past several decades since it has undergone major changes due to the impacts of excessive nutrient and pollutant loads whilst simultaneously experiencing a significant reduction in freshwater inflows. In this presentation we outline application of a 3D finite-volume hydrodynamic-biogeochemical model that is being used to explore the controls on the emergence of hypoxia and algal bloom risk. The model was configured to simulate oxygen, nutrients, organic matter, sediment, the seagrass Halophila sp, and phytoplankton biomass (including a nuisance dinoflagellate group), and applied at two different scales of operation to accommodate the different time-scales of questions being assessed. In particular, the validation approach is highlighted and used to demonstrate the fine numerical resolution that is required to resolve upstream migration of the salt-wedge during low-flow conditions when water quality problems become the most significant. Scenarios exploring the effectiveness of management interventions including artificial oxygenation and nutrient reduction within urban drains are assessed and being used to guide their ongoing implementation.