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Trickle down technology

Issue 18 | November 2006

Photography: Greg Ford and Melissa Di Ciero

Thirsty work: Dr Tim Fletcher and Dr Ana Deletic with a Permapave porous paving slab.

The efforts of two Monash researchers may help persuade the urban planners of the world's driest continent to save precious rain water by using a new type of paving for public areas.

Porous paving -- bricks and slabs that allow rain water to seep through to the ground beneath -- has been a popular innovation in Europe for many years.

However, the potential of these thirsty bricks and slabs to reduce the burden on urban water systems has met with resistance from governments and urban planners in drought-affected Australia.

Dr Ana Deletic, from Monash's Faculty of Engineering, believes the cautious attitude of these decision-makers can be traced back to earlier trials of porous paving that failed in Melbourne and Sydney.

But now Dr Deletic and her colleague Dr Tim Fletcher, from the Department of Civil Engineering, have received federal funding to work with Victorian paving manufacturer Dymon Industries Pty Ltd and a Melbourne community environmental project, Ceres Incorporated, to test and refine porous pavement technology for use in Australia.

They have been awarded a three-year, $90,000 Australian Research Council Linkage Grant for the project.

"Porous paving comes in many different forms and is used widely overseas, particularly in the UK and northern Europe," Dr Deletic says.

"Many a new open car park or street cul de sac in the UK use paving made of porous bricks, and it looks so much nicer than asphalt or concrete.

"Planners and builders in Australia are still afraid that porous paving will fail. But we believe the model we are working on is an excellent design and, as with any technology, its success often depends on how you use it."

The Australian paving product Dr Fletcher and Dr Deletic are working to refine is called Permapave. It is formed from crushed rock that is combined with a binding agent and then set into a slab shape.

Dr Fletcher says Australia urgently needs to find ways to re-use stormwater runoff.

"With water demand in Australia approaching, and sometimes exceeding, limits of sustainability, there is a pressing need to find alternative water sources," he says.

"Replacing impervious areas with porous pavements will allow urban stormwater to be treated and harvested for re-use. Waterways will be protected from pollution, and the vast quantity of urban stormwater generated -- which is actually equivalent to the total amount of reticulated water currently supplied in Australia -- can be harvested to sustain cities."

Dr Fletcher says the Permapave technology works because, in the binding process, lots of tiny voids or spaces are left between the small stones. "Rain water can filter through the slab that way," he says.

By developing novel pavement block and sub-base materials, the pollutant-removal capacity of these systems will be further enhanced.

Dr Deletic says cost has been a stumbling block to the acceptance of porous paving. "Local councils and building project developers must carry the cost of this paving, which is more expensive than standard paving," she says.

"But there are savings too, because they don't have to install drainage pipes under the paving, and they don't have to provide stormwater storage either.

"There is also another environmental advantage -- the process of the water dripping through the paving filters removes nasties like heavy metals from road pollution so that stormwater returning to our waterways is cleaner."