by Ruth Cooper
With heavy rainfall causing flooding in New South Wales and Queensland recently, we took a look at the interesting ways local councils are harnessing the power of stormwater.
From creating thriving wetlands to reducing demand on potable water supplies, here are four initiatives that turn stormwater from a waste into a resource.
Big plans for Small Creek
A Queensland council is working on an ambitious project to transform 1.6 km of concrete drain into a living waterway by harnessing the power of stormwater.
Ipswich City Council, in partnership with engineering firm Bligh Tanner, is rehabilitating Small Creek. Once a meandering stream, the waterway was replaced with a concrete channel in the early 1980s.
Bligh Tanner Director, Water and Environment Alan Hoban said this isn’t an unusual situation.
“There was a school of thought in the ‘70s, ‘80s and ‘90s that we really had to drain our cities, and that stormwater was a problem and the best way to deal with it was to straighten and channelise our creeks and get that water away from urban areas as quickly as possible,” he said.
“What we’re increasingly learning is that in doing that, we’ve lost some fantastic creeks, it exacerbates flooding downstream; we’re also getting really poor water quality and losing those really key environmental values that everyone treasures in southeast Queensland.”
Construction on the project started in 2018, with completion expected by 2023. The area will be transformed with the addition of native vegetation, pools and shallow running water.
“In its current state, the channel contributes to the degradation of water in our creeks and rivers, as the hard surfaces in urban areas result in a dramatically increased volume of runoff that contains more pollutants,” a factsheet from Ipswich City Council said.
“This dirty water travels very quickly down the channel, causing erosion and poor water quality in downstream Deebing Creek. The Small Creek project will help reduce these problems.”
The first 800 m has been finished, with 7000 new trees planted along with 220,000 new plants to slow water flow and provide habitat for wildlife. There are also new bicycle and pedestrian paths, helping residents connect with the waterway.
A new water source
In Salisbury, about 20 km north of Adelaide, residents have access to ‘Salisbury Water’ – the council’s term for the non-potable recycled water it delivers through a 150 km network of purple pipes to parks, reserves, schools, industry and some new residential developments.
The water is a mix of groundwater and stormwater runoff, which is captured and treated in more than 50 wetlands throughout the area. During periods of high rainfall, excess stormwater that has been filtered through the wetlands is injected into an aquifer for storage. This is used as needed to supply Salisbury Water customers.
Salisbury has more than 50 wetlands that treat stormwater. Image: City of Salisbury
Not only does Salisbury Water provide an alternative source for non-drinking purposes, the project also reduces the amount of stormwater runoff, in turn protecting ecosystems downstream.
“The volume of stormwater that flows annually into the Gulf St Vincent is equivalent to our total consumption,” the City of Salisbury website states.
“Just the stormwater flowing through Salisbury is equivalent to 26% of Adelaide’s take from the River Murray in an average year.”
Creating wetlands also helps with flood mitigation, treats water, increases local biodiversity and provides open spaces for recreation.
Features of the constructed wetlands include:
- trash racks to collect large pieces of litter and debris;
- gross pollutant traps, which combine a trash rack with a sedimentation basin to allow solids suspended in the water to settle;
- sedimentation or detention ponds to filter mulch and fine sediments;
- reed beds to filter slow-moving water;
- weirs to control the levels of water in different parts of the wetland; and
- flow or diversion structures to regulate inflows to the wetlands and ensure very high flows are diverted away from sensitive areas.
Going green
Water storage tanks taking shape at Alma Park. Construction was completed last year. Image: City of Port Phillip
Completed in October last year, the City of Port Phillip’s Alma Park Stormwater Harvesting System captures and treats stormwater, storing it under the Alma Park sports field before using the water to irrigate the field and nearby parks in the area south of Melbourne.
Saving drinking water was a key driver for the project, the council said on its website.
"Up to 18 ML of stormwater will be captured and reused by this Alma Park system each year,” it said.
“This will significantly reduce the need to irrigate the park area with drinking water. It will also provide an alternative source of water for our open spaces and will increase our water security, particularly in drier times.”
The City of Port Phillip collaborated with Melbourne Water on the $2.7 million project as part of the Living Rivers program. This offers councils funding, expertise and guidance to improve stormwater management.
The scheme includes: a gross pollutant trap; a 230-square-metre bioretention garden to filter nutrients and heavy metals from stormwater; storage tanks with total capacity of more than 1 ML; a small treatment shed that includes ultraviolet treatment; and an access track that allows heavy vehicles to access the site while maintaining grass coverage.
Underground engineering
Built on land that was once a network of wetlands and creeks, Sydney’s Green Square is prone to flooding during heavy rain. The solution was to build a 2.4 km underground stormwater drain capable of carrying 30,000 L of water/second from Epsom Road, Zetland, to an existing stormwater system at Alexandra Canal.
New stormwater pipes ready to be installed. Image: Sydney Water
The project, developed by the City of Sydney and Sydney Water, was four years in the making and won the 2019 Infrastructure Project Innovation Award at the Australian Water Association’s NSW Water Awards last year.
A water recycling plant treats water from the drain so it can be used by thousands of residents in the Green Square town centre.
It involved a range of creative solutions to ensure life could go on as normal above ground while construction was carried out, including micro-tunnelling to allow tunnel boring machines to install 1.8 m diameter pipes up to 12 m underground.
Announcing the official opening of the drain in November, City of Sydney Lord Mayor Clover Moore said the $140 million project was an example of how water resources could be used to reduce demand on drinking water, minimise flood risk, improve water quality and enable development.
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