The Northern Beaches Local Government Area (LGA) has a mix of freshwater creeks, wetlands and groundwater ecosystems flowing into coastal lagoons, estuaries and iconic beaches. To address the potential impacts of stormwater runoff on waterway health, Council engaged Alluvium Consulting Australia Pty Ltd to undertake a Stormwater Management Study (the Study) for the LGA.

The Study followed a NSW Government framework to help councils develop their own waterway health objectives and to prioritise catchments and determine management strategies.

By following this framework for our waterways, the Study identified:

• Community environmental values (e.g. aquatic ecology and riparian habitat) and uses (e.g. recreational amenity such as swimming and fishing)
• The existing condition of the waterways as well as the future desired condition (e.g. to maintain or improve the existing condition)
• Existing land use and potential future development within each waterway catchment over the next two decades.

Based on this information, the Study developed a Stormwater Management Strategy that outlined draft targets for stormwater quality and quantity for each catchment across the LGA.

The objective of the study was to develop a Stormwater Management Strategy and qualitative targets for stormwater quality and quantity for each catchment in the LGA to inform the Northern Beaches Council’s Local Environmental Plan (LEP) and Development Control Plan (DCP).

The Study recommended the following:

Categorisation of the catchments in the LGA into four groups with specific stormwater management targets based on the existing condition of the waterways as well as current and future pressures on the community environmental values and uses of the waterways. These are:

• Group 1 and 2 catchments - more stringent stormwater quantity and quality targets are recommended to protect creeks and/or downstream receiving waters with high ecological value (targeting runoff volume, suspended solids, nutrients such as phosphorus and nitrogen, litter and coarse sediments) or high recreational values (such as swimming). This is referred to as neutral or beneficial effect on water quality. This includes creeks such as McCarrs, Deep and Carroll Creeks.
• Group 3 catchments have highly disturbed creeks and/or poor condition receiving waters that will have targets that aim to mitigate the impact of stormwater runoff to improve condition of the waterways (targeting the same pollutants and addressing quantity as for Group 1 and 2). This includes creeks that are highly disturbed located in catchments with existing imperviousness > 30% (examples are Manly, Brookvale and Careel Creeks).
• Group 4 catchments, discharging directly into well flushed permanently open estuaries or the ocean, will focus on managing discharge of litter and coarse sediments, as pollutants such as excessive levels of nutrients have little impact on open, well-circulated marine waters (examples includes catchments such as North Harbour, Dee Why Beach and Newport Beach catchments).

A map outlining the draft stormwater management approach for each catchment for inclusion in the Northern Beaches Council planning controls. The map will allow landowners and developers to see where their property lies and what stormwater quality and quantity targets they will be required to meet should they need to submit a development application.

Do you agree with the catchment group, draft waterway objectives and stormwater management targets for each sub-catchment?