Trevallyn Dam valve replacement works

22 December 2015

Hydro Tasmania will undertake work in early 2016 to replace three large dewatering valves built into Trevallyn Dam. The valves were installed in Trevallyn Dam when it was built in the 1950s.

The $6 million 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 timing of the project 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 three large and heavy valves from the bottom of the dam, and because the work is being undertaken in a spillway. There is a risk of Lake Trevallyn spilling over the dam 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.

“We will be working around the clock so the project can be completed as quickly as possible, but will limit noisy activities to daytime hours.”

Hydro Tasmania has spent many months consulting with people who live near Trevallyn Dam, to understand how the work may impact them and what can be done do to minimise these impacts. Other stakeholders have also been consulted during preparation for the works.

“Users of the surrounding area may experience some inconvenience as a result of the work. We will endeavour to minimise this wherever possible, but there will be some unavoidable impacts to ensure workers’ safety, and we apologise in advance for any inconvenience,” Mr Rumsby said.

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 2.5 cubic metres per second through Cataract Gorge, which is above the statutory requirement of 0.42 cubic metres per second. Water flow into the Gorge below the dam will be approximately half the usual flow during the work.

There are expected to be three occasions during the project when the flow will need to be stopped entirely to enable specific work to be carried out safely. The longest will be up to 36 hours.

“Hydro Tasmania recognises this is a busy period for visitors to Cataract Gorge downstream from the dam,” Mr Rumsby said. “We will implement measures to ensure any flow stoppages avoid peak times when there will be the highest number of people enjoying the Gorge.

“We plan for these stoppages to occur in the evening and overnight as much as is possible. There will be no stoppages on public holidays and Hydro Tasmania will do everything it can to avoid weekends.”

An existing access track is being extended to the worksite at the base of the dam to allow safe access. This will be removed and rehabilitated on completion of the work. The picnic area at the Trevallyn Dam lookout will be closed to the public from 4 January until the works are complete in early March as this will form part of the worksite.

During the work there will be no capacity to provide flushing flows or recreational water releases. To reduce the likelihood of water quality issues that have been known to occur in First Basin during summer months, Hydro Tasmania will provide a flushing flow prior to the start of the work on January 2.

Public notices outlining the work will be published in the Examiner newspaper on Wednesday 23 December and again on Saturday 2 January. Signs have been erected in the local area to advise people of the project and highlight safety issues.

Information about the valve upgrade project is available on Hydro Tasmania’s website:  http://www.hydro.com.au/energy/upgrades-and-maintenance

Ends.                                                           

Released by Ian Colvin (03) 6230 5800.

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