Benalla dam's 'piano key' spillway a first for Victoria

A NEW weir that is the first of its kind in Victoria could potentially be used on the state’s largest water storage.

North East Water recently finished works on an upgrade of Benalla’s Loombah Dam spillway — one of two dams on Ryan Creek — by using an innovative “piano key” spillway.

The more cost effective and efficient method is now being considered for use on Dartmouth Dam, project manager Miguel De Oliveira said.

A spokeswoman for the Murray Darling Basin Authority, which operates the dam, confirmed it was something that would be considered.

“We’ve looked at that design and we’d contemplate it for a potential future dam safety upgrade, but it wouldn’t be something done in the near future,” she said.

The piano key spillway is designed to increase the capacity of a dam to safely pass flood flows.

It’s estimated to increase flows by more than four times what a conventional, same-sized spillway allows.

The design has been used widely in France and the US but is new in Australia.

Its use wasn’t even planned for the Loombah Dam upgrade — engineers were forced to re-examine their plans of using a traditional labyrinth spillway once works began.

“We had to modify the design when excavation works found that rock on the site was extremely hard,” Mr De Oliveira said.

“Following discussions with the contractor and designer, a piano key spillway was then constructed.”

Mr De Oliveira said there were no negatives to the new model of weir — potentially paving the way for it to be used more widely in the future.

Not to mention the added benefit of a stunning visual effect, he added.

“When the dam spills, it will be an impressive sight, with the water cascading through the unique design,” he said.

The $1.8 million project began last year and is a self-balanced structure built from precast concrete.

Works included excavation and removal of rock and earth the equivalent of five Olympic-sized swimming pools, 2000 tonnes of concrete laid, 95 tonnes of steel reinforcement and 20 vertical anchored precast panels.

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