Flood spectre prompts urgent review of Opuha Dam

Civil Defence has ordered a review of the Opuha Dam near Fairlie after fears were raised about a possible collapse during a heavy flood or a significant earthquake.

John Norton, director of the Ministry of Civil Defence and Emergency Management, says there is no immediate safety threat.

The 400m-long and 50m-high earth dam partially collapsed during construction on Waitangi Day, 1997.

The latest safety concerns come after a report commissioned by power giant Meridian Energy highlighted possible problems over seepage levels.

Meridian chief executive Keith Turner wrote to Sir Peter Elworthy, chairman of the Opuha Dam Partnership, about his concerns.

Mr Norton said: "It's a significant issue. There is a public safety issue and we need to be clear that it's being addressed."

Sir Peter said public safety was his company's highest concern, but he was puzzled by Meridian's actions.

"No one's talking about threats or danger. But we are taking notice of this."

He said extra monitoring had been initiated and a planned safety report had been brought forward.

The dam partnership's own consultant was happy the structure was safe and performing within its design requirements. The consultant, Tonkin and Taylor, had been peer-reviewed by two other sources, Sir Peter said.

Opuha Dam is 50 per cent owned by electricity business Alpine Energy and 50 per cent by the local community. It was built to provide water for Timaru and to replenish the Opihi River, provide irrigation to nearby farms and to generate a small amount of electricity.

Mr Norton said action had been taken because the alert came from a reputable source.

"I've spoken to their [Meridian's] consultant.

"I'm a civil engineer and I think the only way to deal with this is to undertake a full safety review."

Mr Norton said one of the reasons the action was taken so promptly was the history of the dam.

About 200 people were evacuated from the tiny communities of Butler and Stratheona, downstream of the dam site, after the 1997 collapse.

Stock were lost and fence lines were damaged after the floodwaters caused the collapse of 200,000 cu m of earth rock silt and gravel into the Opuha River.

Environment Canterbury, the regional council, was left nursing a $576,000 repair bill for its damaged flood defences.

A council report into the collapse identified a series of process failures in the construction which meant the dam could not cope with a one-in-six-year flood event.

Mr Norton said his department was first alerted about the potential problem by the office of the Minister for State Owned Enterprises last Thursday.

Civil Defence had met the Opuha Dam Partnership, and representatives of the Timaru District Council, Environment Canterbury, and the Mackenzie District Council.

As a result of the meeting, Civil Defence had asked for monitoring to be instituted at the dam site, which was begun on Monday, and for the dam company to come up with the terms of reference for a safety review. Civil Defence wants the terms of the review, which will be carried out independently, by the end of January.

Engineers working for Meridian subsidiary Dam Watch had been commissioned to look into the possibility of raising the dam by 6m.