Water Quality Monitoring for Long-Term Impact Assessments of the Warriewood Valley Urban Land Release

Approximately 110 hectares of land in the Warriewood Valley area (within the Pittwater Council local government area), was approved for release for urban development by the then NSW State Government Minister for Urban Affairs and Planning in 1997. The Valley catchment drains to three creeks that connect and flow to the Warriewood Wetlands and Narrabeen Lagoon, a sensitive waterway that opens episodically to the ocean. To ensure the surface water quantity and quality from the development areas are managed in a sustainable way, a Water Management Specification was prepared. The specification encourages the use of innovative techniques in the field of water management and water sensitive urban design. In particular, the Specification sets stringent compliance requirements for water quality. These requirements are adaptive in light of results from ongoing baseline water quality monitoring. This paper presents a summary of the results from pre-development monitoring (including one full year's worth of baseline monitoring), outlines the current processes operating in the local system and provides some guidance on the practical aspects of assessing the long-term impacts of residential subdivision. The principal conclusion that can be drawn from the work undertaken to date is that the adaptation of the recently released ANZECC guidelines (2000) should be within the context of the processes operating in the local system. A short, medium and long-term approach to the meeting of water quality objectives is proposed as being a more achievable goal for highly degraded and impacted systems where water sensitive urban design features are implemented.