Rock may be imported for part of the embankment of the Waimea Community Dam, which is under construction in the Lee Valley, near Nelson.
Under the original plan, excavated rock from the build site was to be used for the rock fill dam, a $104.4 million project that is being managed by Waimea Water Ltd.
However, Waimea Water chief executive Mike Scott said some of that rock was causing concern.
The concern related to “the behaviour of the rock in the drainage zones”, which included the upstream face and the bottom of the embankment.
Much of the rock had met expectation but “other areas where rock is to be used in the embankment became a concern” after initial testing in January. Further testing and trialling was under way.
“It was unforseen so it was a surprise,” Scott said. “I’m not feeling particularly stressed. It feels like a speed bump rather than we’ve hit the wall.”
The issue was “fairly solvable”, and the design and construction would be adjusted to suit.
Scott agreed the company may have to buy some rock but said it was too early to say whether that would be the case and if so, what effect it could have on the overall cost of the project.
“This is really fresh,” Scott said. “We’ve got to do the lab analysis and testing first.”
Waimea Water Ltd is responsible for managing the construction, operation and maintenance of the dam. It is a joint-venture partnership between Tasman District Council and Waimea Irrigators Ltd. The geology at the site has long been tagged as one of the major risks for the project.
Scott’s comments come after Waimea Water chairman David Wright spoke to Tasman District councillors via video conference on Thursday during an open council meeting.
Wright confirmed bedrock had been found.
“It has required a bit more excavation than what we might have wished, however, we have found bedrock,” Wright said. “We can anchor the dam so there are no issues around that aspect going forward.”
He also said there had been “some issues” with the rock fill needed for the embankment. The team was working through the options, which may include importing some rock.
More detail would be provided for a full council meeting, scheduled for late March.
“We will be briefing shareholders on that certainly by the 26 March council meeting or earlier, if known,” Wright said.
Councillor Anne Turley said she found it embarrassing to be asked at community association meetings about difficulties at the dam site and not know about them.
“I would ask that if there are issues that we do get … early disclosure rather than hearing it in the community,” Turley said. “You know, it’s not a good look.”
Wright said it was fair comment and talked about a “trade off” between having time to make a decision and briefing the shareholders.
“We have got to be able to come to a considered position before we’re able to come to you and other shareholders with a view on what that might mean to timing/cost to complete,” Wright said. “We’re doing that as expeditiously as we can but we are equally aware what that does is potentially allow for speculation in the community.”