The replacement of the gates in the heart of the Cradle Mountain-Lake St Clair National Park will ensure the historic structure continues operating reliably for decades to come. 

The project team battled snow and heavy rains to install the massive gates, which each weigh almost 3.5 tonnes and measure around five by three metres.  

Making the $1.9m project even more complex was its location at a lagoon off the deepest lake in Australia situated within the Tasmanian Wilderness World Heritage Area. 

Located at the southern end of Lake St Clair, the radial gates at the lagoon regulate water flows into Lake King William and the River Derwent as part of the Tarraleah hydropower scheme. 

Hydro Tasmania Project Manager Bevan van Rooyen said the gates were an important part of the state's hydropower system, despite only being operated occasionally. 

"The gates might only operate once every couple of years, but when we need them, they have to work exactly as intended," Mr van Rooyen 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 originals in appearance, dimensions and operation to preserve their heritage value, but with modern engineering improvements. 

Hydro Tasmania's consulting business Entura carried out detailed inspections of the gates and identified areas that required additional strengthening. An Aboriginal heritage survey was also undertaken before construction commenced. 

To protect the environment, the team constructed a crane pad on Hydro-vested land. This enabled a long-reach crane with an extension of almost 70 metres 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 Mr van Rooyen. 

"Lifting the gates into position required millimetre-level precision and had to be done without damaging the environment in any way." 

Environmental safeguards were implemented during the project, including the use of geofabric to capture sediment, algae and any potential contaminants, along with certified clean fill and multi-season weed monitoring before and after construction. 

Tasmanian contractor Crisp Bros & Haywards delivered the project with support from a network of local subcontractors providing painting, scaffolding, civil works and labour services. 

Mr van Rooyen said the project highlighted the value of working with local industry. 

"We love working with local businesses and Crisp Bros & Hayward and their subcontractors did an excellent job, and delivered the quality result we wanted," Mr van Rooyen said. 

Mr van Rooyen said the project team had delivered a stronger asset for the future, protected an extraordinary place and supported local industry. 

"If no one notices that anything has changed at Lake St Clair, then we've done our job properly," Mr van Rooyen said. 

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