Geologist warns of 'jelly bowl'

19:33, Jun 29 2012

A leading Christchurch geologist has given his support to a green corridor wetland park idea for the eastern red zone.

Dr Mark Quigley said it could be a good way of ensuring housing was not rebuilt on land that was vulnerable not only to liquefaction from earthquakes, but also to flooding.

The Avon-Otakaro Network wants to transform red-zoned residential land along the Avon River into a park reserve and has submitted a petition supporting the plan to Parliament.

Quigley, senior lecturer in active tectonics at Canterbury University, yesterday spoke at a "designing for resilience" conference at Lincoln University. He said he had not signed the network's petition, but supported the idea.

Quigley likened Christchurch to being on a "jelly bowl" of gravel and sand.

Much of the eastern landscape was already vulnerable to flooding, sea surges or far-field tsunamis.

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He said the earthquakes had increased the flooding risk.

Rivers had narrowed and shallowed from lateral spread, and already low-lying areas had dropped by up to 40 centimetres since the September 2010 quake. This was equivalent to what the sea level was expected to rise in an entire century.

Modelling of aftershocks had also shown there was a very high probability of another liquefaction-inducing earthquake in the next 50 years – and about a 10 per cent chance of this happening in the next year.

"If a magnitude 6 was close enough to Christchurch, that could facilitate more liquefaction and more lateral spreading in those vulnerable areas."

Quigley said it was important these factors were considered in the rebuild of the city.

He did not want to see vulnerable unremediated land go on sale when aftershocks died down in the next 10 to 15 years.

"People might say, `I'm going to buy on marginal land because it's cheaper and my insurance company will buy into it'," he said.

"I would hate to see that happen. Bad land-use decisions now will come back on us, or our kids, or their kids," he said.

The cost of more payouts through the Earthquake Commission would be a cost the nation would again have to bear.

The Press