Multimillion dollar upgrade proposed for lake
A multimillion dollar upgrade is proposed for Lake Opuha.
Opuha Water will lodge resource consent applications with Environment Canterbury and the Mackenzie District Council in a plan to improve the lake's capability.
The dam's lower weir has a spill capacity of 110 cubic metres per second, designed to wash out in a one-in-five-year flood.
Opuha Water wants to increase its spill capacity to 250 cumecs, which involves the construction of a new spillway capable of releasing 140 cumecs.
It would then be capable of withstanding a one-in-20-year flood.
That would cost $1.7m while Opuha Water is investigating the incorporation of a micro-hydro facility that would have a power output of between 300 and 400 kilowatts.
The main driver is the $250,000 replacement cost of a fusible section that washes away if flows reach more than 100 cumecs.
It washed away in 2003 and 2009.
Opuha Water chief executive Tony McCormick said he hoped the consent would be lodged by Christmas.
The company will take on debt to cover the project cost. The economics of the $1.8m hydro proposal are marginal at present and the company is looking to reduce the cost of installation.
"What we are aiming to do is increase capacity so we can release more water than what we have been. It's to improve our flood-management capability."
Mr McCormick said more flow capacity would also allow for better flushing flows downriver.
"It means we will be able to operate the lake better."
He said the new design would allow for higher lake levels.
Opuha Water planned to spill 40 cumecs for several hours in a test earlier this year but the flow only got up to 32 cumecs.
It was part of a collaborative effort with Environment Canterbury and the National Institute of Water and Atmospheric Research to address concerns around algal and didymo growth.
There had been complaints about the level of didymo in the system just below the dam.
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