Stormwater is a term used to describe 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, that gets swept up in its 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.
Managing stormwater better
Stormwater management systems should be designed to:
- protect public health and safety
- protect public and private infrastructure and buildings
- protect and restore the health of waterways, estuaries, wetlands and oceans
- improve the liveability of urban communities.
When conventional urban development occurs, most of the soil and vegetation is replaced with impervious surfaces such as roads, carparks, houses and other buildings.
Increased imperviousness results in less rainfall infiltration into the soil and ultimately provides less water to replenish the local groundwater aquifers. It also increases the volume and speed of stormwater runoff produced by rainfall.
The increased runoff raises the risk of flooding of houses, roads, parks and downstream environments and increases the amount of pollutants discharged into waterways, estuaries, wetlands and oceans.
Many ecosystems rely on stormwater to contribute to the recharge of groundwater. This recharge is also important to replenish groundwater that we use for scheme water supplies, agriculture, industry and irrigating gardens and public open spaces.
Conventional urban drainage systems were designed to reduce local flooding by channelling stormwater and intercepted shallow groundwater quickly into waterways, estuaries, wetlands, oceans or basins. However, this often has damaging environmental and social consequences, such as algal blooms that can kill wildlife and prevent recreational use of water.
To manage stormwater better, urban drainage systems should mimic natural water cycle processes wherever possible, with the aim of creating water-sensitive cities and communities.
This water-sensitive approach includes site-responsive designs that manage small rainfall events as close to the runoff source as practical, includes vegetation within the urban landscape and within drainage management systems, replaces impervious surfaces with pervious surfaces, provides overland flow paths, and retains natural water bodies and natural drainage flow paths.
Stormwater management roles
The Department of Water’s role in stormwater management is to provide floodplain mapping for major river systems, prepare drainage and water management plans. In addition, we provide Western Australian stormwater management principles, criteria and guidelines, and assess urban development proposals.
In Western Australia, local governments are responsible for managing local drainage networks. Local governments assess urban development proposals, construct local road and drainage systems, and maintain drainage networks. Please refer to the latest version of the Local Government Guidelines for Subdivisional Development (Institute of Public Works Engineering Australia WA Division Inc. 2012) for local government subdivision and drainage management guidelines.
The Water Corporation is one of the key service providers for urban main drainage infrastructure in parts of the Perth metropolitan region, while also responsible for rural arterial drains in some parts of the south-west of Western Australia. The Water Corporation assesses urban development proposals if they are located in a drainage catchment area that contains Water Corporation drainage infrastructure.
- To access detailed information about how to manage stormwater, see the Stormwater management manual for Western Australia
- The Decision process for stormwater management in WA
- For summary information on stormwater management and water sensitive urban design, see the water sensitive urban design brochures