The Marine Estate Management Strategy 2018–2028 (MEMS) identified that a key threat to estuarine water quality in NSW is catchment runoff from agricultural and urban areas. The associated MEMS Implementation Plan outlined that improving water quality in agricultural and urban catchments applying pilot projects of the Risk-based Framework for Considering Waterway Health Outcomes in Strategic Land use Planning Decisions was the highest priority action.
The first pilot project was completed by Alluvium (and project partners) for Lake Illawarra that is a waterway under increasing pressure from existing and future urban diffuse source water pollution and modified flow regimes.
The Lake Illawarra pilot project focused on investigating a range of water sensitive design options arranged into treatment scenarios sized to achieve current management targets and test draft revised targets. Over 20 treatment scenarios were tested including lot, street and centralised water sensitive design measures configured in a range of treatment series.
An economic assessment was completed to evaluate how modified management targets and different treatment series would influence lifecycle costs. The economic analysis outcomes indicated that scenarios including larger centralised water sensitive design measures would be more cost effective for managing stormwater runoff from future development than scenarios relying on distributed lot and street scale treatment.
The economic assessment results also indicated that the total lifecycle cost of a runoff quality management strategy for a typical primarily low density residential development in the Lake Illawarra catchment may increase substantially where higher management targets are adopted.
The pilot project outcomes also identified that development incorporating water sensitive design measures has the potential to significantly lower erosion potential in the waterways when compared to development without measures.
The project outcomes were provided to Council partners for consideration in updating of planning controls for future development in the Lake Illawarra catchment.