29 May 2013 — Since 2008 we have kept more than four million litres of stormwater in our suburb of Chippendale, NSW at a cost to residents and businesses of less than $300.
This one-off cost was what we had to pay to buy drains that leak – agricultural pipe covered with geofabric.
We put the leaky drains into the road verges in front of houses where the owners agreed to them going in to replace the pipes that, up until then, had taken rainwater away as a waste product to the local stormwater pipes in the roads.
Since 2008 the operating costs are nil. So over the five years we’ve kept over 20 million litres here to water our trees and plants, increase the amount of tree and plant canopy and make our road gardens more productive.
It was associate professor John Argue from Adelaide University in South Australia whose deep and years long research into leaky drains showed what’s possible for those who wish to choose leaky drains and similar low-tech, low-cost engineering solutions to stop stormwater systems wasting city rainwater.
South Australian research on an urban block involved four high-volume water loading tests using mains water over a one-month period in mid-winter 1998. Water was injected into the soil to an amount equal to one year’s average rainfall on the house’s 345-square-metre roof. Gravel drainage absorption pits were installed. Three boreholes downstream of the house were used to measure the resulting flows including where the clay soil met underlying sandstone rock. No direct link could be established between the water injected and flows downstream. This research shows infiltration devices (gravel pits, leaky drains, absorption and soak pits) can be used at clay soil sites with relatively high sandstone bedrock (Epke van der Werf, John R Argue, David van de Pezanitti).
We’re continuing to build leaky drains. We aim to keep over 52 million litres of water here in our suburb at a cost of less than $4000. That’s the estimated cost of the leaky drains we need to buy.
And that’s about a third of the water that falls here each year and is presently wasted as pollution to Sydney Harbour.
It costs us nothing to install our leaky drains. We dig up and cut off the existing pipes ourselves. Then we simply slip in the leaky drain and…voila… a leaking drain to irrigate our vital road gardens.
We’ve made a video showing how easy it is to put a leaky drain outside your place.
You can see Thais, one of our road verge gardeners, showing how easy it is, and it can be done in 20 minutes with four simple tools: shovel, pick, leaky pipe and hacksaw.
This drawing shows the before and after of a leaky drain:
[From Sustainable Food, New South Books, 2012 by Michael Mobbs. Reproduced with permission of the author.]
A leaky drain respects our precious water by putting it to productive use in the road to grow plants and trees in our streets. In doing so, that previously wasted water reduces the urban heat island effect by increasing the shade over the black, hot roads. It also takes the load off stormwater systems and reduces the depreciation and repair costs to them.
The question is why, in this dry country, at a moment of crisis in government funding and declining capacity among our governments – local, state and federal – aren’t low-cost, low-tech, proven infrastructure systems like this being promoted?
My guess is it’s because they’re in the thrall of consultants who are threatened by a drop to their profits, which would be cut by low-cost, simple technology instead of the big pipes in and big pipes out practices that support their business model.
Other options for watering our cities include:
Aquakerb: a 70mm diameter and 1.2-metre long pipe with a slit about 120mm long at the base; placed in the road gutter it directs water to the subsoil to the tree and plant roots.
Soak or absorption pit: a hole 0.5-metres in diameter and 1.2 metres deep with a geofabric liner and rubble inside that holds and disperses rainwater below the surface of the ground to distribute it to tree and plant roots; this works well in high- and low-rainfall areas, and with clay soils (the most water resistant).
Barloch drain pipe water diverter: although this product is no longer available, it’s shown here to illustrate what a good product it was; buy or build something like it. Similar products are available, but they don’t offer three connections for hoses like the Barloch did.
Raingarden: a sunken garden between the road and the verge which holds, stores and absorbs rainwater from the road to mimic the natural flow of water before development. The raingarden surface is about 120 to 300mm below the road level and this holds water during and after rainfall, and allows it to drain from the road by gravity, thereby feeding plantings in the raingarden and preventing nearby waterways being polluted and eroded by stormwater runoff.
Flow-through planter bed: downpipe water is directed to the soil. When the planter bed is full the rainwater overflows and supplies water to the road verge.
Swales: channels built to follow the curves or contours of the land and slow run-off from any area, giving water time to absorb into the soil.
Permeable pavers: as the name suggests, these allow water to soak through to the soil.
*For other water options including information on tanks, filter and gutter systems and the quality of rainwater see Sustainable House.
Michael Mobbs’ book, Sustainable House, details how to build a sustainable project – what works and doesn’t. The book shows how Sustainable House has recycled more than 1.5 million litres of sewage in a five-square-metre garden in Sydney’s inner city suburb Chippendale since 1996, uses rainwater for drinking, solar power for energy and provides accommodation for four people for utility costs of less than $300 a year.