'Tanking' keeps flood at bay

LOIS CAIRNS
Last updated 05:00 15/07/2014
Iain McGregor

John Mackie, Christchurch City Council and civil engineer Stuart Sandy talk about the success of the red zone house they flood protected.

Avonside flood experiment
IAIN MCGREGOR/ Fairfax NZ
KEEPING DRY: Civil engineer Stuart Sandy checks to make sure the waterproof membrane and flood gates are keeping water from getting inside the Avonside house.

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A mock flood has proved that "tanking" could provide some protection to low-lying Christchurch houses.

Last Friday, a red-zoned house in Avonside was deliberately flooded to find out whether tanking - a technology widely used in Britain but new to New Zealand - could be used to minimise the damage to the 80 or so homes in the city that are experiencing regular flooding.

Tanking involves applying a waterproof membrane to the exterior of a house and is one of a range of short-term defence measures the Christchurch City Council's mayoral taskforce on flooding has been testing. The system relies on homeowners covering up vents and door openings with provided guards in the event of a flood.

Council transport and greenspace manager John Mackie said the blue-coloured membrane applied to the house and the flood gates installed across the doors had adequately held the floodwaters at bay, proving the technology was viable. About 900 millimetres of water had been against the perimeter of the house since Friday and only a minimum amount had seeped in.

"We're very pleased with the results," Mackie said. He estimates the cost of tanking at between $15,000 and $20,000 per property.

Aecom civil engineer Stuart Sandy said the Avonside house had been selected to test the technology because it had been badly damaged in the quakes and had severe cracks.

"We chose this house because it is worst case scenario; if you can waterproof this one you can pretty much do any property," he said.

Among those inspecting the property yesterday to see how the tanking performed were Carrick St residents Paula Green and Diane Shannon.

"I'm very impressed with how it keeps the water out," Shannon said after touring the property.

Green, whose house has been flooded three times, was impressed but concerned about the practicalities of the system.

"I would be very concerned about the logistics of having to seal the grills.

"It is impressive but I don't see it as a long-term solution. You wouldn't be wanting to have this year in, year out - it would be quite stressful," Green said.

Mackie said he believed the technology could be designed so that it was easy for homeowners to deploy.

Developing specifications for the installation of the technology was the next step in the process and should be completed within four weeks.

A report would go to the council on the results of the testing. It would be up to councillors to decide whether the council should contribute towards the costs of tanking individual properties.

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