The spillway on the Clarrie Hall Dam will be widened from 22 metres to 35 metres so it can cope better with extreme flood events but there will be no increase in the dam’s capacity from the upgrade.
Councillors recently voted against raising the dam wall, leading to the future of the Tweed water supply potentially becoming the major issue at next year’s council election.
But they have given the green light to the upgrade of the spillway in order to prevent life and property being lost in a major flood.
Indeed the upgrade of the wall, which is now 27 years old, was ordered by the state government following the tightening of safety standards earlier this year.
There is a danger the work could cause water restrictions across the shire because the dam level may need to be lowered during construction. Tweed residents have not had to endure water restrictions since March 2003, when level-3 restrictions were in force for just one month.
An environmental impact study will not be carried out before the work, which is expected to start during 2013 and take six months. A council report said the reconstruction was not expected to ‘impact on the environment, habitat or threatened species’ in the Doon Doon Valley to an ‘unacceptable level’.
The report warns there will be noise and dust during construction and about 60 light vehicle movements per day and a total of 340 heavy vehicle journeys.
The nearby picnic ground will be closed to the public during construction. There may also be a reduction in water quality for some distance downstream at times.
Council’s water manager David Oxenham said a study had found there would be no cost saving by combining the spillway project with construction of a higher dam wall.
‘It’s more cost effective to do the spillway upgrade now,’ said Mr Oxenham.
‘There would be no saving at all by combining these projects.’