The PortsE2 Decision Support System ? An Application of E2

The E2 catchment modelling software was used to build a decision support system, named PortsE2, to support catchment management scenario investigation being undertaken as part of the 'Better Bays and Waterways' initiative. The model developed covers the catchments of Port Phillip and Western Port Bays (Victoria) (Figure 1). PortsE2 has 189 sub-catchments, with a network that supports sub-catchment and basin scale load estimation. It has 12 Functional Units (FU) based on land use, and one Point Source FU. Major water storages and flow control structures are represented, as are major diversions. Point sources are lumped within sub-catchments, and represented by weighted flow and concentration. Five years of climate data (1994-98) drive the default scenario. This period contains dry (1997), average (1998) and wet (1995) years. Five climate-land cover groups (forest west, non-forest west, forest east, non-forest east, and urban) were used to support regionalised flow calibration. Water quality (TN, TSS, TP, Pathogen, Toxicant) parameters were obtained from field data and literature. Management scenarios tested in PortsE2 include land use change, water sensitive urban design (WSUD) interventions, adoption of agricultural best management practices, intensification of agricultural practices, changes to point sources, climate change, and septic tank management. Land use change planned under 'Melbourne 2030' yielded marginal increases in overall loads. An additional 180 t/a of TN is predicted to be generated within the region by 2030, putting an increased strain on the Port Phillip Bay receiving environment. Medium implementation rates of WSUD had the potential to reduce approximately 450 t/a of TN (8%), 5,300 t/a of TSS (22%), 70 t/a (4%) of TP and 15 t/a of toxicants (43%). Adoption of agricultural BMPs cut approximately 55 t/a (1%), 3200 t/a (3%), 5 t/a (<1%) and 0.2 t/a (<1%) of TN, TSS, TP and toxicants, respectively, with climate change scenarios yielding similar scale TN, TSS and TP reductions of approximately 310 t/a (2%), 3500 t/a (3%) and 95 t/a (5%). Moderate agricultural intensification had no discernible effect on load, as did septic tank numbers, while significant reductions were found to arise from point source management. Results for a medium level bushfire scenario showed Port Phillip Bay would be most affected by fire in the Upper Yarra, with increased generation of 35% TSS and 4.5% TN. A fire in the Bunyip/Tarago area was found to generate almost 25% more TSS for Western Port. These limited scenarios suggest WSUD interventions may offer the greatest load reductions. Development and testing of these scenarios showed the significant strengths of E2 for this kind of work, with two areas identified for improvement being point source representation and model parameterisation based on small scale stormwater modelling results.