Hydro Tasmania is replacing three large dewatering valves originally built into Trevallyn Dam in the 1950s in a complex $6 million project.
In a statement, the Australian utility said the project is vital to the dam's future operation and safety, and will improve the reliability of water released for the environment and for a range of stakeholders. The project is being timed from January to March is to ensure the safety of workers involved.
Project Manager Andrew Rumsby said the valves had reached the end of life and needed to be replaced so Hydro Tasmania can safely provide these releases and manage the level of Lake Trevallyn.
The project is complex in that it involves removing and replacing the three large and heavy valves from the bottom of the dam, and because the work is being undertaken in the dam's spillway. There is a risk of Lake Trevallyn spilling over during the work if there is a lot of rain in the South Esk catchment, which would pose a danger to workers and compromise the worksite.
"The most critical decision was to undertake the work during summer. We recognise this is a popular time for recreation users and visitors but it is also when there is the lowest chance of high rainfall and spill," Mr Rumsby said. "The safety of our people and the general public is a top priority and we have taken a number of actions to ensure their safety, and to protect the worksite during this project."
The highest risk work is being undertaken from mid-January until mid-February and during this time the water level of Lake Trevallyn will be below the normal summer operating range. This will impact on the flow through the Cataract Gorge.
Hydro Tasmania currently provides a riparian flow of 2.5m3/sec through Cataract Gorge, which is above the statutory requirement of 0.42m3/sec. Water flow into the Gorge below the dam will be approximately half the usual flow during the work.
