Stormwater is water flowing over ground surfaces and in natural streams and drains, as a direct result of rainfall over a catchment. Stormwater consists of rainfall runoff and any material (soluble or insoluble) mobilised in its path of flow.
Where there is a superficial aquifer, drainage channels can include both stormwater from surface runoff, and groundwater that has been deliberately intercepted by the drains.
Within the Perth Metropolitan Area, an estimated 830 kilometres of 'main' drains are managed by the Water Corporation and an estimated 3,000 kilometres of 'local' drains are managed by Local Government.
Managing stormwater better
Many ecosystems rely on stormwater to contribute to the recharge of groundwater.
This recharge is also important to replenish groundwater supplies that we use for drinking, farming, industry, horticulture, and irrigating gardens and open spaces.
Roads, roofs and other impervious areas prevent stormwater from soaking into the ground.
Densely developed inner urban areas are almost completely impervious, which means less infiltration into the local groundwater, the potential for more local runoff and a greater risk of both flooding and pollution.
Traditional urban drainage systems were designed to reduce local flooding by channelling stormwater quickly to rivers, wetlands, oceans or basins.
However, this often has negative environmental and social impacts, such as algal blooms that can kill wildlife and prevent recreational use of water bodies.
To access detailed information about how to manage stormwater, see the Stormwater management manual for Western Australia. For summary information on stormwater management and water sensitive urban design, see the Water sensitive urban design brochures.