Retreat is best option for floods, says expert

17:00, Apr 09 2014

Abandoning areas in Christchurch under threat from the effects of sea level rise is "painful" but necessary, a researcher says.

University of Canterbury coastal science lecturer Dr Deidre Hart said for some areas of the city, including the lower Avon and Heathcote river, retreating would prevent the impact of further flooding disasters.

Last month a storm left parts of the city inundated by water.

Hart said floods like last month's would become more common due to sea-level rise.

"When a low-lying city like Christchurch - former coastal plains and swamps - floods, it has to drain out via the sea. If the sea levels are higher, it's harder to drain out to sea."

Sea-level rise, associated with global warming, is a threat facing many cities, but Christchurch's woes have been hastened by the 2011 earthquakes.


The earthquakes caused some city land to drop up to half a metre. Scientists have predicted sea-level rise of one metre to the year 2115 - leaving the city with tough decisions.

Hart said temporary engineering fixes including sea walls, channels, stop banks and pumps were not the way to tackle sea-level rise.

"You temporarily fix the problem and everyone feels safer in that suburb, stay there and no-one worries about retreating. Development then increases with more people in the area.

"But then you get the one in 300-year event which exceeds all the engineering capacity and then you've got a really big disaster on your hands, made worse by not retreating."

Hart said retreating was a painful option that would be felt more in New Zealand because of the culture of home ownership.

"Retreating is very painful because people are moving from their community and houses.

"I'm not saying for one minute that it is easy at all. But the situation can be made worse by not retreating."

Last week the council said it was considering increasing flood management areas by 30 per cent - a figure that could rise further still, it said.

Already 2500 properties were identified in a October 2012 review of flood management area due to the earthquakes.

The Press