In addition to the pollutants carried in stormwater runoff research by Australian researchers is identifying urban runoff as a cause of pollution in its own right.
In natural catchments (watersheds) surface runoff entering waterways is a relatively rare event, occurring only a few times each year and generally after larger storm events. Before development occurred most rainfall soaked into the ground and contributed to groundwater recharge or was recycled into the atmosphere by trees as evapotranspiration.
Modern drainage systems which collect runoff from impervious surfaces (e.g., roofs and roads) ensure that water is efficiently conveyed to waterways through pipe networks, meaning that even small storm events result in increased flows in waterways.
In addition to delivering higher pollutants from the urban catchment increased stormwater flow can lead to stream erosion, encourage weed invasion and can alter natural flow regimes which native species rely on for a range for activities including spawning, juvenile development and migration.
Polluted runoff from roads and highways is the largest source of water pollution in coastal areas today.
Our drinking water supplies, shellfishing waters and bathing beaches are fouled by uncontrolled pollution when rainwater and snowmelt wash over city streets, parking lots, and suburban lawns and pick up toxic chemicals, disease-causing organisms, and dirt and trash. This problem is called urban stormwater pollution. Recent studies have found that urban stormwater rivals and in some cases exceeds sewage plants and large factories as a source of damaging pollutants.