Assessing the effectiveness of three water sensitive urban design (WSUD) measures in SE Melbourne

For over ten years urban catchment engineers have adopted the principles of Water Sensitive Urban Design (WSUD) both in new and existing residential and commercial developments. Despite their widespread use across the Melbourne metropolitan area little data exists on their effectiveness in improving water quality, one of their most important functions. Moreover, existing WSUD guidelines only stipulate that percentage removal of average annual exports of Total Nitrogen (TN), Total Phosphorus (TP) and Total Suspended Sediment (TSS) loads must meet stated efficiencies. Most WSUD measures are sized using MUSIC without reference to site specific water quality data. There are several types of WSUD measures widely used in Melbourne such as raingardens and constructed wetlands. The difference in performance between WSUD types is little known. This study reviews existing catchment monitoring data for three WSUD measures in the Scotchmans Creek and Gardiners Creek catchments of Melbourne's south-eastern suburbs. It investigates how well these measures are performing in their function of improving water quality, through an assessment of dissolved oxygen, turbidity and reactive phosphorus. Preliminary results obtained using the Waterwatch monitoring data for these catchments indicate that some wetlands are not functioning as well as expected. Recommendations are made for improved monitoring and modelling of water quality in these catchments.