THE EFFECTIVENESS OF CONTINUOUS DEFLECTIVE SEPARATION (CDS) POLLUTANT TRAPS IN REDUCING GEOCHEMICAL INPUT INTO URBAN WETLANDS: A COMPARATIVE STUDY OF TWO CONTRASTING STORMWATER

Wetlands of the Swan Coastal Plain are important locales for groundwater recharge. Degradation of receiving waters, such as groundwater, is of major concern in the Perth Metropolitan Region, which relies upon groundwater for approximately 70 % of its total water consumption, and almost 50 % of domestic water supply. It is most important that measures are taken to prevent contamination of this vital resource. Impermeable surfaces in the urban area, such as roofs and roadways, catch and divert rainfall as stormwater runoff (Davidson 1995). The high permeability of the sands underlying Perth results in rapid transfer of stormwater from infiltration basins to the shallow aquifer. Thus, there is considerable interest in stormwater composition and the necessary measures to help reduce contamination of groundwater. The present study investigated a type of gross pollutant trap (GPT) called a continuous deflective separation (CDS) unit. It focused on two separate CDS units installed in urban stormwater catchments of contrasting character and sought to determine their effectiveness in minimizing the flux of stormwater-derived pollutants (e.g., nutrients and metals) to adjacent urban wetlands. The stormwater catchments were located at Blue Gum Lake Reserve and Quenda Wetland in the City of Melville. The catchment feeding the CDS unit at Blue Gum Lake Reserve has an area of 2.62 ha. Land-use within and adjacent to the Blue Gum Lake Reserve is primarily residential. In contrast, the catchment at th