'Stormwater runoff' comprises all forms of runoff from urban areas. It is enhanced by the web of impervious surfaces, including roads, roofs, footpaths, car parks and other structures, and is conveyed to coastal waterways by natural and man-made conduits and drains. The volume of stormwater discharged and the types of contaminants in stormwater are suggested indicators for State of the Environment reporting (e.g. Indicator 2.7 and 2.8 respectively in the Human Settlements Theme) .
Photo 1. Black-winged stilts (Himantopus himantopus) feeding amongst rubbish delivered by stormwater drains at Tuggerah Lake, NSW. (photo by David Balean)
The impacts of stormwater on the coastal environment are many and varied, and are related to the extent, nature and intensity of urban and industrial development . Further, stormwater discharges to coastal environments should increase with size of the coastal population.
Stormwater can locally increase freshwater flow to coastal waterways. Moreover, as stormwater runs over urban surfaces, it may collect a variety of contaminants, and therefore is a diffuse source of pollutants. These contaminants can be divided into five main classes :
Contaminants in stormwater can give rise to fish kills, shellfish closures, eutrophication and related problems (e.g. harmful algal blooms, anoxic & hypoxic events), and can contribute to an overall reduction in biodiversity.
More information on stormwater indicators (e.g. monitoring and design strategies, guidelines for analysis and interpretation, reporting scales etc.) can be found in the Human Settlements volume of Environmental Indicators for National State of the Environment Reporting . The coastal discharges indicator includes wastewater discharges. See also the fact sheet on hermit crabs.