Joe Wagner Group has recently completed a project for CS Energy at their Kogan Creek Power Station and mine area building a spillway to manage future water runoff from an ash cell into a catchment dam, which can be used for initial sediment management and future irrigation.
The ash cell stores waste ash from the power station and when full, it will be capped with soil and revegetated. The new spillway will provide a safe transfer of water once the ash cell is full as part of the site’s rehabilitation process.
Included in the job was work clearing out another full sediment basin so that it could receive overflow from a second pre-existing spillway.
The new spillway was built on a steep slope with the final result having a 16.67% gradient and stretching over 207 metres. It is the largest we have ever built. The works required bulk excavation to dig out the spillway from the hillside and final trim to make sure the surface was smooth enough to lay bitumen geomembrane liner. Trenches were dug down each side in which the liner was anchored. Large concrete anchor beams were also built at the top and bottom of the spillway, with a third buried anchor beam halfway down the slope.
Some existing liner at the head of the spillway needed protecting while we dug out sediment from the basin. We used our 25 tonne Excavator for this task, and it required great precision to ensure we didn’t dig holes into the liner—our GPS technology made this work easier.
We laid shot rock at the top and bottom of the spillway to help filter the water as it ran into the second pond. To protect the geomembrane, our supervisors recommended laying a cushion layer before placing the rock, and this was accepted by the clients as a viable solution.
Between the work on the Spillway and the second sediment basin, we excavated 24,000 cubic metres of material, using some of that material to build up embankments in other areas; laid 2000 tonnes of rock; and poured 60 cubic metres of concrete.
Our team worked well on this project—completing it ahead of schedule, without incident, and no LTIs. Needless to say, our client was very happy.