Engineers to pay cost of fixing cracks in dam project

NELSON - Design problems which have delayed the $2.9 million Wai-iti Dam mean that Tasman District farmers seeking irrigation water now face a further year-long wait because of cracks in some parts of the dam construction.

But costs of extra work required because of deficient design are being met by the design company, Auckland-based Tonkin and Taylor, according to a Tasman District Council engineering manager, Peter Thomson.

The 19.3m-high earth dam on the Kainui Stream in Eighty-eight Valley has been built to store 815,000 cubic metres of water on an 18ha block of land owned by the Tasman District Council.

Council engineering manager Peter Thomson said problems with the concrete conduit surrounding the intake pipe under the dam had required extra work to secure the joints and prevent seepage.

Construction of the dam was to have been completed in October but it will not be finished until "at least Christmas", Mr Thomson said.

The piping system had shown "design inadequacies" during construction, he said.

"Inspection of the completed conduit works showed very small cracks in the concrete at locations we hadn't anticipated.

"Some joints in the concrete pipes were not to our satisfaction, so we decided to put in an additional liner to provide extra protection and prevent cracking and seeping."

Arrival and installation of the liner had delayed the project.

Mr Thomson said he was not prepared to discuss the the extra costs of the project as they were "not relevant to council".

He said the problems were picked up by the design consultants but said council remained confident of that company's work.

Tonkin and Taylor managing director Terry Kayes said the company was undertaking to do the remedial work but did not accept liability for the problem.

"Dams require quite a high level of security and high level of contingency. They need to be safe in a number of ways because there is a lot of energy in terms of water," he said.

"With cracks, there is a potential for ongoing seepage and transport of material where that could have long-term effect on the stability of the dam."

Mr Kayes said the work was being done to ensure the security of the dam.

"I wouldn't want to suggest this is an immediate safety issue.

Mr Thomson said although the problem had caused a delay in the project it would not affect the irrigators, because the main rainfall harvest period was during winter and the dam had not been scheduled to be finished before October, well after the main rainfall period.

"There'll be no benefit to irrigators this summer.

"It's disappointing we can't be storing water at the moment but it's important the project is properly completed to council's satisfaction and then we can take the dam through to its commissioning trials next year."

- NZPA