Work to begin on $3.5m modifications to Lenthall Dam gates
FAILING flood gates at Lenthalls Dam will be upgraded by October but property owners who have suffered through repeated inundation remain dubious about Wide Bay Water's ability to get the job done.
On Monday, Wide Bay Water chief executive Peter Care confirmed much-needed "modifications" would be carried out by engineering consultants GHD and Melbourne-based company Geotech - the same two firms which oversaw the design and installation of the defunct crest gates in 2007.
While the gates were designed to open once water levels reached 150mm above the top gate level, they have systematically failed to do so, leading to preventable flooding and isolation for Burrum River properties.
Cattle grazier Donna Allan's family farm was worst affected.
On Monday, she said the modifications, which would include the construction of a reinforced concrete deflector wall upstream of the gates and the installation of hydraulic cylinders, were likely a "waste of money" as she believed the original design was flawed.
The failure of the gates was subject to a hearing at the Queensland Floods Commission of Inquiry during which Mr Care gave evidence that while the conceptual design of the gates had been successfully installed as party of new dam projects "the design had never been used to raise an existing dam".
The inquiry heard Wide Bay Water had difficulty with all gates, in particular Gate 5, during seven flooding events in four years.
In its final report, the commission recommended the "Department of Environment and Resource Management should require Wide Bay Water, in advance of every wet season, to provide details of its expectation as to the operability of the crest gates if a flood occurs, until such time as all gates have been demonstrated to work as designed".
Asked during the inquiry if the gates would ever work as designed, Mr Care said "I'm not a dam designer ... I could not say that they'll ever work".
The project is expected to cost about $3.5 million and is due to start on April 28 and finish by October, weather permitting.
The 2m high gates were installed to increase the capacity of the dam and designed to rise as the dam level rose to capture water, but automatically lower to control the release of water during a storm.
Mr Care said the technology was an Australian first and based on an idea that was operating in South Africa.
"Unfortunately since their installation the gates have experienced operational issues for a variety of reasons and have failed to remain down during flood events," he said.
"We have confidence in the design as the modifications have been tested using a scale model at the Manly Hydraulics Laboratory."
The project involves building a temporary access track and cofferdam across the spillway approach to allow construction of reinforced concrete deflector walls upstream of the crest gates.
Small modifications to the existing steel crest gates and spillway and installing hydraulic cylinders, sheaves and ropes to existing spillway piers and crest gates to assist in holding the gates down when they are releasing water are also part of the works.
The recreation area will be closed to the public for the duration of the works.
"The project will have no impact on water supplies to residents and businesses," Mr Care said.