Dam weirs upgrade consents to be filed

A multimillion-dollar upgrade of the Opuha Dam's downstream weir system is still on the cards and could get under way next summer.

Opuha Water chief executive Tony McCormick said it would file consents with Environment Canterbury next week.

"It's taken us longer than we would have hoped to get to this stage, but we needed to talk to a lot of the key members of the community this would affect," McCormick said.

"Hopefully they would be satisfied with some of the modifications we have made to our proposal."

McCormick said the downstream weir upgrade could cost about $1.7 million and increase the spillway capacity from 110 cubic metres of water per second (cumecs) to 250 cumecs.

"This would be a big advantage for coping with larger flood events," he said.

Earlier this summer, the dam company experimented with a release of a 40 cumec flushing flow - about four times the average - in an attempt to clean the Opuha and Opihi rivers of didymo and toxic algae.

McCormick said the downstream weir upgrade would assist with future releases.

"We're trying to do everything we can to address anglers' and locals' concerns about toxic algae and didymo. We were pleased with the initial results of this season's release, so we're looking into how we can build on it," he said.

McCormick said a plan to upgrade the dam's hydro generation capacity by two gigawatt hours (GWh) was also "on the table", but might be reconsidered.

It could potentially add another $1.5m to the project.

The dam generates about 26GWh per year.

"It's certainly something we will include in the plans, but the cost could be prohibitive," McCormick said.

"But all things going to plan, we hope to start work on the upgrade of the downstream weir system at least over the summer. It will be the biggest addition since the dam was commissioned in 1998."

The Timaru Herald