Waimea Dam at 'increasing risk' of further delays as dry spell looms

Thursday, 26 October 2023

Waimea Community Dam reservoir, pictured on August 30, 2023.

The Waimea Community Dam is between 91 and 95% complete, but it’s facing one last hurdle – Mother Nature.

Waimea Water Limited presented their quarterly review to the Tasman District Council on Thursday, with chairperson David Wright saying they were becoming “increasingly concerned” about dry weather and the ability to fill the reservoir to augment the river this summer.

Practical completion has now been pushed back until February 2024, 25 months behind the dam’s original plan.

“We need some more rain,” said Ken Smales, Waimea Water’s project director.

Smales said the dam had approximately one million cubic metres of water of the 13 million it was designed to hold, so they were keen to make up the additional 12 million as quickly as possible.

“Unfortunately, all the predictions are that we're in for a dry spring [and] dry summer.

“Although we were predicting we could be filled by December 23, it very much depends on Mother Nature, and it could be into next year before we get water over the spillway … so there’s increasing risk of further delays”.

There were no snags with the budget in the report, with the cost remaining unchanged at $198.2 million.

Councillor Mark Greening said some people in the public had noted that the dam seemed to be dropping.

Tasman District councillor Mark Greening asked why the water in the dam dropped, as had been noted by members of the public.

“You indicated it did drop, you reduced it, so can you explain why you reduced it, why there was a reduction?”

Smales said that there was a thermistor string that criss-crossed behind the concrete wall, which at one point detected a minor temperature change that “could indicate a small amount of water getting through one of the joints in the concrete”.

“So in an abundance of caution, we decided we had the opportunity to lower the dam again to inject some resin grout into that joint and seal it up and then proceed again with the raising, so we took the opportunity to seal it up.”

Smales said most dams, which weren’t fitted with that level of sophisticated monitoring equipment, would not detect that.

“You’d never know if there was a small weep if there was one, but our thermistor chain picked up the temperature differential, and we assumed it was water, a small amount of water leaking through and that was repaired.”

In response to questions from councillor Trindi Walker, who asked if the lack of rainfall posed a monetary risk to the dam or a risk to the health of the river, Smales said the construction consent required them to discharge the minimum flow in the river.

Smales said there was a risk that if they couldn’t fill the dam by February next year, then there was some risk as to what they did with the contractor, to allow them to finish the work, and that would be discussed by the board shortly.

Tasman mayor Tim King said the dam was sized for 100 years worth of demand for both irrigation and urban areas, of which a significant proportion didn’t yet exist.

“So even a dam that's two thirds full or half full, may well provide a significant benefit if there is a very dry summer, particularly latter summer, even though it might not be 100% full.”

According to the presentation, the residual risks that remain include: ongoing unexpected contractor claims, the contractor disputing the decisions of the adjudicator and independent engineer, and the nine disputes elevated to final and binding arbitration.

Waimea Water was preparing for more than two years of disputes, the presentation said.