in Greener Homes on 25 July 2010
Capturing runoff helps keep gardens green and waterways clean.
Thanks to the drought, householders have become fit hauling greywater buckets and relaxed using rainwater tanks. But there’s still another source to tap: stormwater.
“In most places, rain runs off the roof or the paving to the gutters in the street,” says Stuart McQuire, author of Water Not Down the Drain. “On the way it collects rubbish and pollutants and it all flows into creeks and waterways. In Melbourne it ends up in Port Phillip Bay.”
By reducing stormwater, we not only cut pollution in our waterways, but also trap a valuable resource for our gardens.
Mr McQuire also runs an eco-audit business, Green Makeover. His first tip for restricting runoff is to install a tank and catch rainwater before it becomes stormwater. The next thing to consider is landscaping. “Go into the garden when it’s raining and see where the puddles are and where water is flowing,” he suggests.
You can control the flow by creating swales – hollows or ridges that run across the slope of your block. They slow the water, allowing it time to seep into the soil. “Swales can be very subtle. They can be part of your lawn, or they can be mulched and part of your garden,” he says. “They’re great at retaining water for trees or deep-rooted shrubs.
Stormwater gushes across hard surfaces such as concrete driveways. At his house, Mr McQuire has paths that are mulched or made of broken concrete with gaps that let the water find the earth. Gravel or porous paving also allow moisture to soak in.
“You don’t necessarily have to dig up all your concrete. You could retrofit porous sections across a driveway that let the water through,” he says.
The high-cost option for stormwater collection is to install an underground tank that allows water to infiltrate through the soil, or accepts the flow from stormwater pipes. Mr McQuire estimates they cost from $1000 per 1000 litres, installed.
Another way to sop up the excess is to create a rain garden, “a garden that waters itself,” according to Pat Arundell from Rain Gardens Australia.
It’s a demonstration of wisdom, not wizardry. Around the home, the gardens are placed to capture water from downpipes or runoff from hard surfaces. “They can fit neatly into small spaces and they’re very hardy,” says Mr Arundell.
Rain gardens filter out heavy metals, oils and litter, as well as the excess nutrients that can cause algal blooms in waterways. Earlier this year, Melbourne Water launched a campaign aiming for 10,000 rain gardens throughout the city by 2013. The authority has excellent information sheets online, including detailed guides on size, materials and plant selection.
Mr Arundell says the choice of plants is crucial “They need to be able to sustain dry spells, but also have wet feet from time to time.” He’s found many native grasses well suited to the task.
The other non-negotiable element of any rain garden is the overflow – neither your foundations nor your neighbours will appreciate the consequences of poor planning. “You need to design the garden so it can overflow back into the stormwater,” Mr Arundell says. “And you need a plumber to make those connections.”
The same warning goes for swales or other drainage alterations: make sure you consider where the water will go in a downpour.
For more information, see the stormwater guide on Your Home.