in Greener Homes on 6 March 2011
Harvesting stormwater is essential in a sustainable city
CONSTRUCTION has just begun on a stormwater capture system in Darling Street, East Melbourne. The project, funded by the City of Melbourne, signals a big shift in the public pipelines.
The scheme will divert stormwater from existing drains in adjoining streets and recycle enough water each year to fill nearly 20 Olympic swimming pools. The water will be captured in an underground tank, treated, stored and used to keep nearby parks and trees lush.
The technology has been developed by Biofilta Stormwater Solutions and engineering firm Cardno. It uses natural filters comprised of triple-washed sand and carefully selected indigenous plant species.
Biofilta director Brendan Condon says: “The microbes that live on the roots of the plants break down nutrients and utilise them. Heavy metals get bound up in the top layer of sand. The system can recirculate the water for multiple passes so the bugs get more grabs at the pollution.”
The East Melbourne project is the first in a series of in-road stormwater projects that form part of the council’s climate adaptation strategy. It is estimated to cost $750,000 and should be completed by mid-year.
“We’ve got an enormous volume of polluted stormwater sheeting off the urban environment, creating problems in rivers, creeks and waterways,” Mr Condon says. “And it’s a phenomenal untapped resource that will help protect cities against future climate challenges.”
Professor Tony Wong, director of the Centre for Water Sensitive Cities at Monash University, agrees that we must shift our mindset about stormwater.
“Stormwater is often seen as a nuisance we should get rid of very quickly,” he says.
He argues that our standard approach not only misses a chance to improve our water security, but also causes erosion and degradation of our waterways and Port Phillip Bay. The scale of the problem grows as the city expands and housing density rises.
“Creeks are now getting more water than they would normally get in any storm event. The traditional infrastructure is less able to cope, so we see water on the road more frequently now than in the past,” Professor Wong says.
In a natural environment, only about 15 per cent of rainwater flows into waterways, filtered through the soil. The rest evaporates or is transpired by plants.
Hard surfaces flip the ratio. “When we knock the trees down and pave the land, we find that the creeks now get 85 per cent of the rainfall,” he says. “The numbers vary from city to city, but with any urbanisation, natural creeks receive about four to eight times the water that used to flow into them. Our urban creeks are suffering from too much water.”
A number of other local governments – including Port Phillip and Kingston by the bay – have begun to install raingardens to treat and minimise stormwater runoff.
Professor Wong believes that within two decades, up to a third of Melbourne’s water consumption could come from stormwater.
“Having gone through the last drought, a lot of councils are now looking at stormwater to help with the public space maintenance,” he says.
“It’s not just about water as a commodity. It’s about water providing the means for liveability and for the greening of the city. With water we can bring some biodiversity back and influence the microclimate to protect against the effects of heatwaves.”