Thomson River Fishway

We are planning to build the Thomson River Fishway to improve the health of the river system and protect the future of some threatened species including the Australian Grayling. The project is to install a low impact, environmentally sensitive designed fishway near the heritage listed Horseshoe Bend Tunnel.

This tunnel is important socially, historically and is much loved by bushwalkers and visitors. The design for the fishway is currently being finalised, but the vision is to allow native migratory fish to access an extra 85km of habitat in the upper reach of the Aberfeldy River and provide connectivity between the Gippsland Lakes and the Alpine region.

Many questions have been asked over the life of this project. You can view these questions and answers for more information

Close up of an Australian Grayling being held in two hands

Need

Horseshoe Bend Tunnel is four kilometres from Walhalla on the Thomson River. It was built in 1911 and 1912 to drain water from the Thomson at Horseshoe Bend to allow for alluvial mining of the river bed. It gained heritage status in 2002 (if you’re interested in the history of the tunnel, please download a copy of the Heritage Report part one and part two). Horseshoe Bend Tunnel now acts as an artificial fish barrier to the alpine regions. Flows have only gone round the bend two per cent of the time in the last 13 years. This has severely impacted upstream migration to the unreachable 85 km of habitat for migratory fish.

Fish migration is extremely important in the lifecycle of many of our native fish, including the protected Australian Grayling. The Grayling is listed as vulnerable under the Environment Protection and Biodiversity Conservation Act 1999.

About the Australian Grayling

The Australian Grayling is a small to medium-sized, slender, silvery fish with soft-rayed fins. It lives in south-eastern Australia, including Victoria, Tasmania and New South Wales.

The Grayling has a very short life span of 2-3 years and migrates throughout its life cycle between fresh and marine waters. Adult Graylings live in freshwater river systems. They move up and down the river looking for food and during autumn migrate to near the estuary to spawn. Its eggs are swept downstream towards the sea and the adults return upstream. The young fish remain in the sea for about six months before returning to freshwater.

In our region it can be found in the Thomson, Macalister, Avon, Latrobe, and Tarwin rivers.

The Grayling needs our help

Threats to the long term future of the Australian Grayling include

  • artificial fish barriers (like  Horseshoe Bend Tunnel)
  • introduced fish species
  • low river flows
  • river regulation by dams
  • nutrients in waterways
  • its short and complex life cycle of needing to move up and downstream to reproduce
Staff onsite at the geotechnical assessment

Planning

Over the last few years we have worked with our stakeholder group to develop a fishway design and walking track that preserves the heritage and social values of the tunnel and improves recreational access and restores flows around Horseshoe Bend.

A range of options were considered before settling on the current fishway design. The depth of the fishway varies from a maximum of 2.7m deep upstream grading down to no excavation (over a length of about 200 metres along the 1km dry riverbed). The average depth is 1.4m. The width also varies to a maximum of seven metres wide. In context, the valley floor at Horseshoe Bend varies from 20m to 50m wide. Throughout the consultation period we have explored every option to minimise the size of the fishway. The result of this work is a low flow and a visually low impact fishway that will present itself as a meandering waterway.

There are four main elements to allowing fish passage around Horseshoe Bend.

  • Splitting the flows between the tunnel and around Horseshoe Bend. A 60% to 40% split is proposed
  • The design of a fishway entrance, at the tunnel outlet, to attract fish past the outlet
  • Passage over existing rock riffles and;
  • A constructed fishway through the old river channel near the tunnel inlet.
Grey box. Decorative image

Works

Works are expecting to start work in Autumn 2018.

Grey box. Decorative image

Outcomes


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Thomson River Fishway Questions

This page answers many of the questions that have been asked over the life of this project so far.