Predictions of liquefaction ignored

A 4WD vehicle in a crack in the suburb of Avonside. Photo / Brett Phibbs

Developers fought to build on Christchurch land where liquefaction was likely to occur, says a former regional council boss.

Concern is growing about how much development has been allowed on land prone to liquefaction.

When the earthquake struck on February 22, grey silt rose to smother whole streets and neighbourhoods, particularly in the eastern suburbs.

While there is reluctance to play the blame game when so much of the city has yet to recover from the quake, it will be a major question for officials once Christchurch is on its feet again.

Former Environment Canterbury chairman Sir Kerry Burke said the liquefaction occurred pretty much where ECan reports had predicted.

When compiling a report on earthquake risk for ECan some years ago, scientists drilled about 600 holes around Christchurch to map where liquefaction was likely to occur.

"They turned out, tragically, to be pretty accurate, although most of the land had been built on then," he said.

However, he was sure there had been cases where developers argued against a position ECan had taken over the risk.

"One of the lessons of the earthquake is perhaps we should pay more attention to science rather than to legal arguments from guys with deep pockets," he said.

Geological sciences lecturer Mark Quigley said ECan's mapping of likely liquefaction was right for a lot of areas.

"Some was worse and some not as bad [as predicted]," he said.

A major focus of people studying liquefaction this time was to compare it with the maps of the 1990s.

"Those maps were used long before some of the new suburbs that were continued to build."

Dr Quigley himself was a victim in one of the much older suburbs, Avonside. His house was "absolutely hammered," and he's removed more than 500 wheelbarrow loads of sand from the property.

He did not want to comment on allowing building on land where the liquefaction risk was known.

"It's up to the city council and politicians to comment on why they built there," he said.

Dr Mark Yetton, who did much of the work on the liquefaction maps, was not available for comment yesterday.

Garry Moore, who was mayor of Christchurch for nine years to 2007, said the council had always been really cautious about allowing building where there was that risk.

Staff visited Kobe in Japan after its earthquake and looked at liquefaction -what they learned was used in the planning for the Ferrymead bridge and Blenheim Rd overbridge, he said.

For subdivisions, if there had been any doubt at all, he thought it would have been raised with the council and raised in the [consent] process.

Christchurch East MP Lianne Dalziel said the issue was one to look at later and not a priority for her constituents now.

Most of Christchurch had a liquefaction risk, including well-established suburbs, she said.

"This time liquefaction in Avondale and Bexley was much worse than last time. People used to say Pacific Park shouldn't have been built, but Bexley was hit really hard, too."

The liquefaction risk was much greater than just for the areas that were affected this time, and it might be the preparation of the land and foundation building standards were part of the problem as well, she said.

At present her concerns are more immediate: "My neighbours and I haven't had power, water, or sewerage for 16 days now. We hope to get power in the next couple of days but have no idea when we'll have water and sewerage again."

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