Hydro Tasmania has completed a A$1.9 m infrastructure upgrade at St Clair Lagoon in Tasmania, Australia, replacing eight radial gates that have been used to manage water flows in the Derwent catchment since the early 1930s.
Located at the southern end of Lake St Clair, the gates regulate water flows into Lake King William and the River Derwent as part of the Tarraleah hydropower scheme. The site is within Cradle Mountain-Lake St Clair National Park and the Tasmanian Wilderness World Heritage Area.
The replacement gates each weigh almost 3.5 tonnes and measure around 5m by 3m. Hydro Tasmania said the work was carried out in challenging weather conditions, including snow and heavy rain.
Hydro Tasmania Project Manager Bevan van Rooyen said the gates remain an important part of Tasmania’s hydropower system despite being operated infrequently.
“The gates might only operate once every couple of years, but when we need them, they have to work exactly as intended,” he said. “The gates are manually operated and are important for regulating lake levels and controlling the release of water downstream. They’re also a valued part of Tasmania’s hydropower heritage.”
The replacement gates were designed to match the appearance, dimensions and operation of the original structures while incorporating modern engineering improvements.
Hydro Tasmania’s consulting business Entura carried out detailed inspections and identified areas requiring additional strengthening. An Aboriginal heritage survey was also undertaken before construction began.
To minimise the environmental impact of the work, the project team constructed a crane pad on Hydro Tasmania-vested land. A long-reach crane with an extension of almost 70m was then used to lift the gates into position without entering the waterway.
“The biggest challenge was working within the Tasmanian Wilderness World Heritage Area and making sure we did exactly what we said we were going to do,” said van Rooyen. “Lifting the gates into position required millimetre-level precision and had to be done without damaging the environment in any way.”
Other environmental safeguards included the use of geofabric to capture sediment, algae and potential contaminants, as well as certified clean fill and multi-season weed monitoring before and after construction.
Tasmanian contractor Crisp Bros & Haywards delivered the project, supported by local subcontractors providing painting, scaffolding, civil works and labour services.
Hydro Tasmania said the completed work will strengthen the asset for future operation while maintaining the appearance of the historic infrastructure.
