Water-sensitive urban design (WSUD) is a land planning and engineering design approach which integrates the urban water cycle, including stormwater, groundwater, and wastewater management and water supply, into urban design to minimise environmental degradation and improve aesthetic and recreational appeal.BMT WBM 2009, "Evaluating options for water sensitive urban design – a national guide: Prepared by the Joint Steering Committee for Water Sensitive Cities: In delivering Clause 92(ii) of the National Water Initiative", Joint Steering Committee for Water Sensitive Cities (JSCWSC), Canberra, viewed 18 September 2011 <>. WSUD is a term used in the Middle East and Australia and is similar to low-impact development (LID), a term used in the United States; and Sustainable Drainage System (SuDS), a term used in the United Kingdom.
Common approaches include reducing potable water use and collecting greywater, wastewater, stormwater, and other runoff for recycled use. Infrastructure design may be modified to enable water filtering, collection, and storage.
Background
Traditional urban and industrial development alters landscapes from permeable vegetated surfaces to a series of impervious interconnected surfaces resulting in large quantities of stormwater runoff, requiring management. Like other industrialized countries, including the United States and the United Kingdom, Australia has treated stormwater runoff as a liability and nuisance, endangering human health and property. This resulted in a strong focus on the design of stormwater management systems that rapidly convey stormwater runoff directly to streams with little or no focus on ecosystem preservation. This management approach results in what is referred to as urban stream syndrome. Heavy rainfall flows rapidly into streams carrying pollutants and sediments washed off from impervious surfaces, resulting in streams carrying elevated concentrations of pollutants, nutrients, and suspended solids. Increased peak flow also alters channel morphology and stability, further proliferating sedimentation and drastically reducing biotic richness.
Increased recognition of urban stream syndrome in the 1960s resulted in some movement toward holistic stormwater management in Australia. Awareness increased greatly during the 1990s with the Federal government and scientists cooperating through the Cooperative Research Centre program.Brown, R, and Clarke, J 2007 "The transition toward water sensitive urban design: the story of Melbourne, Australia", Report No. 07/01, Facility for Advancing Water Biofiltration, Monash University, Clayton, VIC Increasingly city planners have recognised the need for an integrated management approach to potable, waste, and stormwater management, to enable cities to adapt and become resilient to the pressure which population growth, urban densification and climate change places on ageing and increasingly expensive water infrastructure. Additionally, Australia's arid conditions mean it is particularly vulnerable to climate change, which together with its reliance on surface water sources, combined with one of the most severe droughts (from 2000–2010) since European settlement, highlight the fact that major urban centers face increasing water shortages. This has begun shifting the perception of stormwater runoff from strictly a liability and nuisance to that of having value as a water resource resulting in changing stormwater management practices. According to the United Nations Environment Programme, climate change is intensifying water-cycle disruptions—such as altered rainfall patterns and shrinking snowpack—which in turn increases the importance of integrative urban water-management strategies like water-sensitive urban design.https://www.un.org/en/climatechange/science/climate-issues/water
Australian states, building on the Federal government's foundational research in the 1990s, began releasing WSUD guidelines with Western Australia first releasing guidelines in 1994. Victoria released guidelines on the best practice environmental management of urban stormwater in 1999 (developed in consultation with New South Wales) and similar documents were released by Queensland through Brisbane City Council in 1999. Cooperation between Federal, State, and Territory governments to increase the efficiency of Australia's water use resulted in the National Water Initiative (NWI) signed in June 2004. The NWI is a comprehensive national strategy to improve water management across the country; it encompasses a wide range of water management issues and encourages the adoption of best practice approaches to the management of water in Australia, which include WSUD.Council of Australian Governments, 2009, "Intergovernmental agreement on a national water initiative", Council of Australian Governments, Canberra, viewed 18 September 2011, <>.
Differences from conventional urban stormwater management
WSUD regards urban stormwater runoff as a resource rather than a nuisance or liability. This represents a paradigm shift in the way environmental resources and water infrastructure are dealt with in the planning and design of towns, and cities. WSUD principles regard all streams of water as a resource with diverse impacts on biodiversity, water, land, and the community's recreational and aesthetic enjoyment of waterways.
Principles Source: Protecting and enhancing creeks, rivers, and wetlands within urban environments Protecting and improving the water quality of water draining from urban environments into creeks, rivers, and wetlands Restoring the urban water balance by maximizing the reuse of stormwater, recycled water, and grey water Conserving water resources through reuse and system efficiency Integrating stormwater treatment into the landscape so that it offers multiple beneficial uses such as water quality treatment, wildlife habitat, recreation, and open public space Reducing peak flows and runoff from the urban environment simultaneously providing for infiltration and groundwater recharge Integrating water into the landscape to enhance the urban design as well as social, visual, cultural, and ecological values Easy, cost-effective implementation of WSUD allowing for widespread application.
Objectives Source: Reducing potable water demand through demand- and supply-side water management Incorporating the use of water-efficient appliances and fittings Adopting a fit-for-purpose approach to the use of potential alternative sources of water such as rainwater Minimising wastewater generation and the treatment of wastewater to a standard suitable for effluent reuse and/or release to receiving waters Treating stormwater to meet water quality objectives for reuse and/or discharge by capturing sediments, pollutants, and nutrients through the retention and slow release of stormwater Improving waterway health through restoring or preserving the natural hydrological regime of catchments through treatment and reuse technologies Improving the aesthetic and the connection with water for urban dwellers Promoting a significant degree of water-related self-sufficiency within urban settings by optimizing the use of water sources to minimise potable, storm, and waste water inflows and outflows through the incorporation into urban design of localised water storage Counteracting the 'urban heat island effect' through the use of water and vegetation, assisting in replenishing groundwater.
Techniques Source: The use of water-efficient appliances to reduce potable water use Greywater reuse as an alternate source of water to conserve potable supplies Stormwater harvesting, rather than rapid conveyance, of stormwater Reuse, storage, and infiltration of stormwater, instead of drainage system augmentation Use of vegetation for stormwater filtering purposes Water efficient landscaping to reduce potable water consumption Protection of water-related environmental, recreational, and cultural values by minimising the ecological footprint of a project associated with providing supply, wastewater, and stormwater services Localised wastewater treatment, and reuse systems to reduce potable water consumption, and minimise environmentally harmful wastewater discharges Provision of stormwater or other recycled urban waters (in all cases subject to appropriate controls) to provide environmental water requirements for modified watercourses Flexible institutional arrangements to cope with increased uncertainty and variability in climate A focus on longer-term planning including in related domains such as water demand management A diverse portfolio of water sources, supported by both centralised and decentralised water infrastructure.
Common WSUD practices Common WSUD practices used in Australia are discussed below. Usually, a combination of these elements are used to meet urban water cycle management objectives.
Road layout and streetscape
Bioretention systems Bioretention systems involve the treatment of water by vegetation prior to filtration of sediment and other solids through prescribed media. Vegetation provides biological uptake of nitrogen, phosphorus, and other soluble or fine particulate contaminants. Bioretention systems offer a smaller footprint than other similar measures (e.g. constructed wetlands) and are commonly used to filter and treat runoff prior to it reaching street drains. Use on larger scales can be complicated and hence other devices may be more appropriate. Bioretention systems comprise bioretention swales (also referred to as grassed swales and drainage channels) and bioretention basins.
Bioretention swales Bioretention swales, similar to buffer strips and swales, are placed within the base of a swale that is generally located in the median strip of divided roads. They provide both stormwater treatment and are. A bioretention system can be installed in part of a swale, or along the full length of a swale, depending on treatment requirements. The runoff water usually goes through a fine media filter and proceeds downward where it is collected via a perforated pipe leading to downstream waterways or storages. Vegetation growing in the filter media can prevent erosion and, unlike infiltration systems, bioretention swales are suited for a wide range of soil conditions.
Bioretention basins
Bioretention basins provide similar flow control and water quality treatment functions to bioretention swales but do not have a conveyance function. In addition to the filtration and biological uptake functions of bioretention systems, basins also provide extended detention of stormwater to maximise runoff treatment during small to medium flow events. The term raingarden is also used to describe such systems but usually refers to smaller, individual lot-scale bioretention basins. Bioretention basins have the advantage of being applicable at a range of scales and shapes and therefore have flexibility in their location within developments. Like other bioretention systems, they are often located along streets at regular intervals to treat runoff prior to entry into the drainage system. Alternatively, larger basins can provide treatment for larger areas, such as at the outfalls of a drainage system. A wide range of vegetation can be used within a bioretention basin, allowing them to be well integrated into the surrounding landscape design. Vegetation species that tolerate periodic inundation should be selected. Bioretention basins are however, sensitive to any materials that may clog the filter media. Basins are often used in conjunction with gross pollutant traps (GPTs or litter traps, include widely used trash racks), and coarser sediment basins, which capture litter and other gross solids to reduce the potential for damage to the vegetation or filter media surface.
Infiltration trenches and systems