THE four spillway gates previously used to control outflows from Leslie Harrison Dam have been removed as part of Seqwater’s Dam Improvement Program.
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 percent 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, measuring 11m across and 4m 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,” Mr Dennis said.
“This equipment has previously been used when removing the gates for routine maintenance.
“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 southeast Queensland to where it’s most needed,” he said.
“Our water security is currently very high following summer and autumn rains.
“The combined volume of our 12 key storages is 98 percent.”
For more information about the Dam Improvement Program click here.