Timaru's low liquefaction risk

MATTHEW LITTLEWOOD
Last updated 05:00 26/03/2014
Timaru liquefaction map

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Timaru is unlikely to be at risk of liquefaction in the event of an earthquake, according to a major geotechnical assessment.

The report, released yesterday, revealed most of the district would be unlikely to be blighted by the issue which hit Christchurch.

Environment Canterbury geological hazards analyst Marion Gadsby said the report was the first of its kind for the Timaru district in more than a decade.

"This report confirms a lot of what we already knew, but it provides more detailed information," she said.

"It's a very useful resource for planning purposes. Liquefaction did not result in any deaths [in Christchurch], but it made the damage to the land and buildings that much worse."

According to the report, the most susceptible areas were Washdyke Lagoon and Saltwater Creek, and near Ashbury Park.

However, these areas were considered to be a "moderate" potential risk at worst.

"The area south of Timaru port has a very low susceptibility to liquefaction, but there may be some pockets of sand which could lead to small amounts of liquefaction," the report said.

Dr Gadsby said it would likely require a magnitude 7 or higher earthquake near Timaru to cause major liquefaction problems in the susceptible areas.

The latest testing indicated Caroline Bay was less susceptible to liquefaction than previously thought. The Port Loop Rd embankments were also unlikely to be at risk of major damage.

Dr Gadsby said the report should help the Timaru District Council with its district plan review.

"It should mean that in most residential or light commercial development proposals would not require further liquefaction assessments. It's good news over all," she said.

"However, I should stress that this report analyses liquefaction risk only. You need to investigate for hazards other than liquefaction - for example, for susceptibility to land slips or flooding."

The district council had also asked ECan to commission an assessment on Geraldine in the wake of increased development.

However, based on the soil types, the liquefaction potential for Geraldine was low.

GNS scientist Andrew King said most of New Zealand would be far less susceptible to liquefaction damage than Christchurch.

"You need a number of factors, such as loose ground, swampy surfaces and a high water table. Christchurch had all three of these things," he said.

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- The Timaru Herald

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