May 13, 2004

‘Seep-through’ paving leads by example

North Shore City Council is showcasing a new kind of seep-through car park surface in the hope of encouraging others to follow suit. The paving, on top of the new Silverfield wastewater storage tank at the North Shore Events Centre, is one way the council is working to deal with the city’s stormwater problems.

The use of ‘permeable paving’ that allows rainwater to seep through, instead of concrete, is designed to reduce surface run-off which can lead to flooding. It also helps cut down the level of pollutants being discharged into streams and the sea.

North Shore City works and environment committee chairperson, Joel Cayford, says it is important that the council leads by example with the extended car parking area.

“This shows developers what they can do to create a better, more sustainable environment for the benefit of the whole city.

“Council is walking its talk through this project. I am hopeful it will trigger other permeable paving projects across the city. It sure needs them,” he says.

The paving works by letting water through gaps between the concrete blocks, then passing it through fine sand and a layer of filter cloth before letting it settle in a retention trench of coarse gravel.

Most of the impurities are removed before the water is released into the stormwater system at a controlled rate to help prevent overflows in heavy rain.

The trial is part of Project CARE, North Shore City Council’s long term programme to improve beach water quality.

The council designed the 6500 cubic metre Silverfield storage tank to reduce overflow events into Wairau Stream and onto Takapuna and Milford beaches, from an average of 12 a year to an annual average of two.

The tank, which was scheduled to take 18 months to build, is now 80 per cent complete and will be finished as planned in July this year.

Using permeable paving for the car park on top of the wastewater tank will increase the cost of the overall project by $100,000, bringing the total up to $6.2m. The extra cost is off set by lower maintenance costs, and not having to put in other stormwater control measures such as ponds and pipes in.

ENDS

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