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Stormwater

Diverting water from the stormwater drainage system to use as a water supply is a mainstream approach in many South Australian towns and cities.

Stormwater is used along with recycled wastewater, groundwater, and roof rainwater for watering parks and sportsgrounds, toilet flushing and industry. The use of these water sources reduces the need to use potable drinking water for activities that don’t require a potable water supply.

Stormwater harvesting and reuse can:

reduce reliance on traditional water resources such as the River Murray, reservoirs and groundwater
improve water quality in our waterway and coastal waters by reducing stormwater runoff, including pollutants
improve local amenity and deliver green landscapes and appealing water features in open spaces by providing an additional water source
reduce the volume and frequency of stormwater flows that can cause erosion in waterways or lead to flooding and drainage issues.

Intercepting, harvesting, cleaning and using stormwater are an important part of the state’s approach to urban water management. Better management of our stormwater not only provides an additional water supply, it is also an important part of an integrated approach to achieving the broad ranges of benefits listed above.

South Australia has been a pioneer of urban stormwater harvesting since the 1980s. We were an early leader in the application of technologies for ‘aquifer storage and recovery’, and wetland treatment for pollutant removal. Water harvesting in the City of Salisbury has been at the forefront of water management since the 1990s. Today similar stormwater harvesting practices are common across metropolitan Adelaide.

In South Australia, stormwater management is a responsibility that is shared between the state government, local government and private landowners. Reflecting this shared responsibility, the South Australian Government and the Local Government Association (LGA) of South Australia have partnered in the formation of the Stormwater Management Authority (SMA).

Download our Stormwater Strategy for background information, South Australia’s goals and a description of the ways in which stormwater can be used.

Today, runoff diversion at a street or site scale is being introduced alongside of the larger stormwater wetland and harvesting systems.

Local capture of rainfall

Today many new stormwater management projects are likely to be site or street scale projects that retain rain water in the landscape for use close to where it falls. This approach can reduce the need for large scale infrastructure to manage large volumes of water. Other benefits of intercepting rainfall before it enters the stormwater drainage network is that it reduces the flow volumes in drains and can provide water for local vegetation without the need for extensive pipe distribution networks.

Examples of on-site and/or street scale runoff diversion projects include:

rainwater tanks
streetscapes and gardens designed for water retention (e.g. pervious vegetated areas that encourage infiltration and water uptake by plants)
roof gardens and green roofs
permeable paving in carparks, driveways, footpaths and roadways
streetscape ‘rain gardens’
street scale retention basins

Local rain capture projects can be considered at two broad scales, at the site level and at the street level.

On an individual site or allotment local capture of rainfall includes the capture of roof runoff in rain water tanks, the use of porous paving or infiltration trenches. Water collected in rain water tanks can be plumbed in to the house to provide an additional water source for a household.

At a whole street scale capture of rainfall involves the collection of rainfall runoff from the road surface before it enters the large stormwater trunk mains. Water is collected to be used locally in the urban landscape, for example to help plants (e.g. street trees) to grow. Street scale diversion includes road raingardens, porous paving, roadside swales and small ponds in parks.

Street scale and site scale rainfall capture activities are likely to continue to be a significant part of urban stormwater management alongside the larger stormwater harvesting activities described below.

Many examples of local rainfall capture projects around South Australia can be viewed on an interactive map produced by Water Sensitive SA.

Stormwater harvesting

Large scale stormwater harvest projects involve the capture, treatment, storage and use of stormwater that is taken from large stormwater pipes or drains. Features of these systems include:

capture of relatively large volumes of water from the stormwater system during wet periods of the year
treatment to remove sediments and pollutants, most commonly in specially designed treatment wetlands
storage of the cleaned water, often in local aquifers (underground water) close to the treatment site
extraction and use of the water during dry periods for irrigation and other activities; often this occurs close to the storage, but sometimes long distribution pipelines are needed.

There are many stormwater harvesting schemes across greater Adelaide that between them capture approximately 6 billion litres of stormwater per year. This is approximately 3% of the water used in the city. It is estimated that with further investment the upper limit for annual stormwater harvest volume could be increased to more than 20 billion litres per year.

Stormwater contains pollutants including sediments and nutrients. Stormwater harvesting schemes use a variety of techniques to clean water before it is stored in aquifers. This includes sediment traps, constructed wetlands and other filters. The pollutants removed by capturing the stormwater would otherwise flow into Gulf St Vincent. Stormwater harvesting projects also reduce the volume of water that flows out to the gulf.

Once the stormwater has been treated it needs to be stored until needed in the dry months. A common technique for storing the treated water is managed aquifer recharge, which involves injecting the water underground so that it can be extracted for irrigation and other uses during dry periods.

Stormwater harvesting schemes associated with managed aquifer recharge are summarised in the 2017 audit of Managed aquifer recharge schemes in Adelaide.

Regional towns and cities also harvest and use stormwater. In the Murray region, there are stormwater reuse schemes in Karoonda, Lameroo, Loxton, Murray Bridge and Pinnaroo.

Stormwater harvesting projects around South Australia can be viewed on the interactive map produced by Water Sensitive SA.