What is stormwater?
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.
Why manage 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.
Our role
The Department of Water provides leadership on managing stormwater as a resource that has important social, environmental and economic values. This principle is promoted in the Stormwater management manual for Western Australia. The stormwater management objectives, principles and framework provided in the manual have been summarised here.
To provide a guide to the process for addressing stormwater management issues during land development and when improving existing practices, the department has published Decision process for stormwater management in WA.
The department's Water and Land Use Coordination Program focuses on the implementation of integrated land and water planning. The department is a partner to Better urban water management (WAPC, DoW, WALGA, DEWHA, 2008). This document identifies a framework for the implementation of integrated land and water planning which adopts the staged hierarchy of the state's strategic and statutory land-use planning decision-making processes.
The Department of Water is responsible for developing strategies and management plans to protect the quantity and quality of water resources, protect infrastructure from flooding and enhance the living environment for the community. To provide guidance and baseline data for planning and development, the Department has embarked on a program to prepare drainage and water management plans to cover the priority urban growth areas between Yanchep and Pinjarra. The plans include:
- catchment specific outcomes, objectives and design criteria
- stormwater and groundwater modelling data and management strategies including storages and flow paths for flood protection;
- water quantity and quality targets and strategies to protect environmental assets;
- guidelines for water sensitive urban design and water conservation.
Additionally, regional water plans are being prepared to bring together existing statutory water management, drinking water source protection, drainage and floodplain management plans into one planning document based on a catchment management approach. The regional water plans and drainage and water management plans will support an overarching urban water management framework whereby Department for Planning, Western Australian Planning Commission, local government and developers obtain necessary data from Department of Water to inform integrated water cycle management and water sensitive urban design. Developers and planners are encouraged to utilise these plans in conjunction with the stormwater management manual to inform greenfield development, urban renewal and other land use planning processes.