19 Jul 2016

Sinking suburb: Thousands of Dunedin homes at risk

4:11 pm on 19 July 2016

A report to be tabled tomorrow by the Otago Regional Council shows almost 3000 homes in the suburb of South Dunedin are just 50cm above sea level.

Emergency services pumping water out from flooded shops.

Flooding in Dunedin in 2015: Almost 3000 homes in South Dunedin are just 50cm above sea level. Photo: RNZ / Ian Telfer

A serious flood in June last year damaged about 1250 properties, and a report released in November by Parliamentary Commissioner for the Environment Jan Wright made it clear the problem of rising sea levels was just beginning. She called it a "slowly unfolding red zone".

Otago Regional Council chief executive Peter Bodeker told Morning Report many residents in the area were still feeling the affects of last year's flooding, which caused $138 million damage.

He said the report clearly showed there was a high risk of long-term surface water and flooding, and that action was needed now.

"The time is right for a community conversation about how best to minimise the combined effects on South Dunedin of high groundwater levels, sea-level rise and land subsidence.''

For the past seven years the council has collected information on South Dunedin's natural hazards and made that information available to the public and Dunedin City Council.

A technical report tying together all of this information will be presented to councillors tomorrow.

South Dunedin is built on soft, silty soils that in the 1800s were a tidal wetland, similar to Hoopers Inlet on the Otago Peninsula.

This is differs from the geological landscape of the rest of the city, which is largely built on a more solid, volcanic rock.

About 2700 homes in South Dunedin lie less than 50cm above sea level.

The Otago Regional Council established three permanent groundwater bores in 2009 and a fourth in 2014 to monitor the relationship between sea level and groundwater levels.

Mr Bodeker said the key finding from this monitoring was the increased likelihood of surface flooding associated with rising sea levels.

"Because there is already a shallow water table beneath South Dunedin, an increase in groundwater levels will eventually result in occasional and possibly permanent surface 'ponding' on parts of the area.

"We believe it is critical the community understands the current and future hazardscape of South Dunedin, and we will be presenting this information to the community over the next two months."

The council report details a number of naturally occurring processes and human activities which together, or separately, could cause flooding in South Dunedin. The report shows how these effects will vary with some areas more affected than others.

Mr Bodeker said Otago Regional Council was working with the Dunedin City Council to talk to the community about the report's conclusions and planning its next steps.

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