Seqwater has removed the four spillway gates at the Leslie Harrison Dam (QLD) as part of their Dam Improvement Program. The gates were previously used to control outflows from the dam.
Seqwater Chief Executive Officer, Peter Dennis, said the gate removal was part of the ongoing program of work at the dam, which supplies about 25 per cent of Redland city’s drinking water.
“Last year we lowered the lake level of Leslie Harrison Dam by lifting all four gates to create a new temporary full supply level until a planned future dam upgrade,” Mr Dennis said.
“In June 2015 we undertook some investigations on the spillway to help inform the scope and timing of an upgrade.
“Once the investigative works were complete, we removed the gates and stored them on site.”
Mr Dennis said each of the four vertical gates weighed 11 tonnes, measured 11 metres across and 4 metres high.
The gates have been in place since 1984, when they were installed as part of a spillway upgrade.
“Seqwater used the on-site gantry crane and rail system to move the gates to the maintenance bay. This equipment has previously been used when removing the gates for routine maintenance,” said Mr Dennis.
“The process took a team of four people half a day for each gate. A 130 tonne crane was then used to lift the gates out of the maintenance bay and onto a concrete storage platform. We had a crane lifting plan to ensure the loads could be lifted without compromising the integrity of the surrounding structure.
“Moving the gates from the maintenance bay to the storage platform took the team another two half days, with two gates moved on each day. The gates will remain on the platform, which was specifically constructed for their storage, while the dam remains lowered.”
Preliminary planning for a future upgrade is now being progressed and will be finalised before the end of 2015.
Mr Dennis said while the temporary full supply level remains in place, the dam operates in the same way as the 22 other un-gated dams in the region. Once inflows to the dam cause the lake level to rise above the spillway crest, water will flow freely out of the dam and into Tingalpa Creek.
“The temporary full supply level does not affect water security for the Redlands as the city is connected to Seqwater’s water grid which enables treated water to be moved around South East Queensland to where it’s most needed,” said Mr Dennis.
“Our water security is currently very high following summer and autumn rains. The combined volume of our 12 key storages is 98 per cent.”