Bigger spillway plan for Lake Opuha

Consent applications are likely to be lodged this month for a multimillion-dollar upgrade of Lake Opuha.

Opuha Water Ltd plans to lodge resource consent applications with Environment Canterbury and the Mackenzie District Council in a plan to increase the lake's capability.

The dam's lower weir has a spill capacity of 110cu m per second (cumecs), designed to wash out in a one-in-five-year flood.

Opuha Water wants to increase its spill capacity to 250cumecs, which requires the construction of another spillway capable of releasing 140cumecs. It would then be capable of withstanding a one-in-20-year flood.

That would cost $1.7 million. Opuha Water has also been investigating building a micro-hydro power generation plant that would have a power output of between 300kW and 400kW.

The main driver is the $250,000 replacement cost of a fusible section that washes away if flows reach more than 100cumecs. It washed away in 2003 and 2009.

Opuha Water chief executive Tony McCormick had wanted to have the consents lodged by last Christmas but there had been a delay in getting responses from other parties.

''Some of the issues appeared to be a little bit different from what we had anticipated; there have been some operational changes.

''We are looking to lodge consents this month and we are pushing ahead with detailed design,'' Mr McCormick said.

The company is aiming to begin construction by the end of this year and plans to take on debt to cover the project cost. The economics of the $1.8 million hydro proposal were marginal and were being revisited, he said.

''The medium-term outlook for electricity prices has softened. We have just this week planned a process to resolve that decision quickly and need to make that decision in the next couple of months.''

- by Al Williams