2007 WSUD for catchments above wetlands
Final report of a study into stormwater management and hydrological objectives for urban development in catchments above coastal wetlands in NSW; and water sensitive urban design (WSUD) solutions) to help protect wetland ecological health.
HCCREMS commissioned Ecological Engineering (R. McManus, T. Wong, and P. Breen) to provide solutions to the challenges faced by Wyong Shire Council. Wyong is a significant periurban growth corridor and hosts many natural coastal wetlands – some of state significance and designated as State Environmental Planning Policy (SEPP) 14 – Coastal Wetlands.
This study looked into the ecological needs of biotic communities associated with coastal wetlands; and the kinds of hydrological regimes required to sustain healthy ecological processes when such wetlands are downstream of urban development. The resulting report and appendices are of value to council staff involved in strategic catchment management, land use planning and development control in NSW.
This study derives stormwater hydrological (water flow) objectives to guide catchment strategic planning and urban development to lessen the impacts that upstream urban development can have on these wetlands.
A method for specifying total catchment hydrological and water quality improvement performance objectives is outlined; and WSUD techniques to achieve this performance are described.
A key finding is that some coastal wetland types need a ‘drying hydrology‘ (as well as a ‘flooding hydrology‘). It is well known that development, with an increase in impervious area, typically increases the volume and duration of runoff that flows from urbanised catchments after common, low intensity, storm events. To ensure the appropriate ‘drying hydrology’ is experienced in wetlands downstream of urbanised areas, the study proposed that ‘dry season flow’ and ‘low spell frequency curves’ be set as objectives to be met by stormwater management and WSUD techniques in urban development in catchments above wetlands.
The projects four key components (with an appendix devoted to each) are:
- Develop a very simple Wetland Classification system of 17 different types, enabling practitioners to undertake a field assessment of wetland type;
- Formulate Water Management (flow) Objectives for catchments – that seeks to quantify the supporting hydrological characteristics required to sustain each wet;
- Consider procedures for determining stormwater quality objectives for catchments above these wetlands; and
- Develop a range of state planning recommendations and local planning provisions to assist councils to implement the water management objectives recommended through the above steps.