Thomson River Fishway Questions

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

The project has been independently assessed, has received all the necessary permits and approvals and is supported by DELWP and Parks Victoria.


Why is the Thomson River system so significant?

The Thomson River is one of the region and state’s most significant and ecologically important rivers, and the creation of a fishway to allow passage between the Gippsland Lakes to the Victorian alpine region is a state priority.

A connected river is a healthy river. The Thomson River can connect the Gippsland Lakes to Victoria’s Alpine region, from Lake Wellington to the Aberfeldy River. The river has excellent water quality and river habitat, particularly in the upper reaches. An Environmental Water Reserve (EWR) provides the opportunity to reach environmental objectives, such as fish spawning, through managed releases.

The Thomson River above Cowwarr Weir and the Aberfeldy River within the Baw Baw National Park are both listed with heritage status in accordance with the Heritage Rivers Act 1992.

What are the ecological benefits to these two Rivers?

Waterway connectivity is critical for fish and aquatic life because it:

  • allows a species to thrive and succeed by providing genetic diversity, allowing fish populations to interbreed
  • provides greater access to food sources and habitat
  • reduces the risk of predator attack by providing more places to live
  • helps a species to return to an area after it has been through disaster (e.g. fire)
  • allows the fish to go through all the critical life cycle stages from spawning, maturing to breeding

The Thomson River is home to eight native fish species that migrate over their life cycle. Fish studies have shown that of these migratory species, only eels are able to populate the river upstream of Horseshoe Bend.

How will native fish benefit from a low flow fishway at Horseshoe Bend?

The new fishway will unlock vast reaches of the upper Thomson and Aberfeldy rivers to native fish.

The fishway will allow fish to swim around Horseshoe Bend, benefiting seven species of native migratory fish and reconnecting Victoria’s Alpine Region with the Gippsland Lakes.

The idea of restoring the river flow at Horseshoe Bend was originally discussed in the 1990s. The current approach was established in 2010 and reflects a new line of thinking, in response to community concerns.

Creating the fishway at Horseshoe bend will enable fish to access an additional 22kms of the Thomson. It is a regular misconception that there is no point creating the fishway, as once the fish reach the Thomson Dam they will be blocked. However, restoring the flow at Horseshoe Bend will also give fish access to 64km of the Aberfeldy River, which is suitable habitat for vulnerable species such as the Australian Grayling.

Concerns have been raised that creating the fishway will allow carp to flourish. While carp can swim long distances, they generally only colonise in suitable water conditions. Carp are most abundant in still or slow flowing water, which is why they are virtually absent from the Thomson River above Cowwar Weir and pose no threat to the upper reaches.

Why a fishway?

The Australian grayling is classed as ‘vulnerable’ in ecological terms as stocks are dwindling. The fishway will allow these fish to migrate upstream as part of their breeding cycle and help to halt the species decline.

There is conclusive evidence that the Horseshoe Bend tunnel stops the passage of migratory native fish (e.g. Australian grayling, tupong, common galaxias) to the upper reaches of the Thomson and Aberfeldy rivers. There is also very strong evidence that these species will repopulate the upper reaches if they could gain access.

There would be considerable ecological benefits to both the Thomson and Aberfeldy rivers by the construction of a fishway within a section of the Horseshoe Bend channel to permit the two-way passage of migratory native fish. Here you can download the 2010 migratory fish study for more information.

What will the fishway look like?

Extensive consultation has been carried out to ensure the fishway balances the significant heritage and cultural values of the site with environmental improvement objectives.

The fishway will be created in the existing river bed and does not consist of concrete structures. A range of options were considered before settling on the current fishway design. The fishway will be 200 metres long and ranging in depth from a maximum of 2.7m deep upstream down to no excavation downstream. The average depth is 1.4m.

The fishway design is 7m wide. When the fishway is dug out, a small amount of land on either side will be battered (an engineering term for creating a receding slope). The purpose of creating this receding slope is to prevent earth slippage.

The battering does add to the width of the fishway, so in some sections it will be up to 7.7m, depending on the existing ground level (which determines the angle of the slope). For the Heritage Impact Statement, that figure of 7.7m was rounded up to 8m. This cross-section of the fishway design provides an illustrated explanation of the 7m design and battering.

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 – see the pictures on our website for more information.

Will the fishway work?

Advice on the fishway design has been provided by Arthur Rylah Institute, migratory fish experts from the private sector and confirmed by an independent Technical Assessment Panel. Over the last 20 years, Victoria has been recognised as world leaders in understanding fish passage and fishway construction. We are very confident that this design will be equally successful.

Why not a different fishway option?

Stakeholder engagement at the start of the project worked through a number of options including use of the use of environmental water, pipe and pool arrangement, a cofferdam at the tunnel entrance and a fishway. The fishway option was found to be the most appropriate based on the criteria of all stakeholders.

A community proposal to cut a small channel through a rockbar was the genesis of the current fishway design. The small channel option was abandoned because it would not have provided adequate flow conditions for fish passage. A larger channel was required but would have resulted in the excavation of the big natural rock bar, an option what was not supported by the community. This option was modified into the current design to use the natural features of the site to provide minimal visual and structural impact and be a fully functional fishway.

Why is the fishway so big?

People have asked why the fishway has to be so large (up to 7 metres wide and 2.7 metres deep) if migratory fish like the endangered Australian grayling are so small.

To make it easier for these small fish to migrate to the upper reaches of the Thomson, the fishway needs to:

  • Be deep enough to enable the water flow down into the old riverbed
  • Be big enough to let enough water pass over the old riverbed so that fish can swim up it
  • Be wide enough to ensure the water flow through the fishway isn’t too fast for small fish to swim through.

The fishway is actually as small as it can be in order to create the right conditions for fish passage. The design and dimensions are based on the natural features of the river and ensuring there is enough water flowing from upstream to enable fish to swim past the outflows from the tunnel outlet.

As part of the design process, we did look at a smaller fishway, but it didn’t meet the requirements for fish passage, and this was verified by the Independent Technical Advice panel.

This is a unique fishway design. Typically, fishways are constructed to overcome barriers such as weir and dams. They are concrete structures consisting of small vertical slots for fish to pass through (e.g. the fishway at Cowwarr Weir).

Although creating the fishway will initially involve an area of the river bed being dug up, the result will be a meandering waterway, and may not be suitable for kayaking or canoeing, as some people have suggested. The fishway will be low-flow and visually low impact – see pictures on our website for more information.

Will water still flow through the tunnel? What about damage to it if it is dry?

Through the consultation and design phase it was found that the minimum requirement to allow fish movement is a 60:40 split between the tunnel and the fishway respectively.

As part of the planning process we commissioned an independent geotechnical report on the stability and structural integrity of the tunnel and the potential impacts of reduced flows. This report did not reveal any risks to the tunnel.

Historically the tunnel has dried out completely during droughts and yet it remains as constructed. Since the commissioning of the Thomson Dam minimum daily flow requirements mean flows will always be maintained. The proposed project will result in 40% less flows through the tunnel and at no time will it dry out.

How will the heritage values of the tunnel be protected?

An important stage of this project is the Heritage Victoria application. In June 2018 Heritage Victoria granted a permit for the project, representing an endorsement of the project design and the balance we have struck between environmental and heritage values.

There will be no works done at or immediately near the tunnel. The design of the fishway has gone through many iterations and been developed to ensure the heritage values of the tunnel and surrounding area will be maintained.

As a further assurance, stringent controls will be in place during construction of the fishway to ensure there will be no damage to the tunnel. This will include the use of vibration monitoring equipment and contractors will work below predetermined vibration thresholds.

How will the project be funded?

Funding for the project was made possible as a result of an offset contribution made by Melbourne Water retailers who had to use a proportion of the Environmental Entitlement during the last drought. As part of the conditions for purchasing environmental water for domestic users, funds were provided to WGCMA to be spent on protecting and enhancing the health of the Thomson River and achieving complementary works to maximise the effectiveness of environmental water once returned to the system. The fishway is the centrepiece of this arrangement.

We do not buy and sell water and such sales are considered and coordinated by the Victoria Environmental Water Holder.

What will the project cost?

Rumour has it will cost $20 million to build the fishway. This is false and unfounded. While the final cost will be determined through the tender and construction phase, the total project budget including all the designs, investigations, and approvals will be less than $2 million. By relative terms this is an inexpensive solution for proving fish passage. By comparison a fishway built on the Yarra River at Dights Falls in 2012 cost $2.5M only for the construction.

Will the project offer good value for money?

Given the location, the sensitivity of Horseshoe Bend Tunnel, and measures required to protect the area, constructing the fishway will be more expensive than undertaking work on a ‘standard’ site.

The fishway will enhance the use of environmental water released annually into the Thomson system and Gippsland Lakes. This water is valuable, and the work will optimise its use to enhance the ecological health of the entire Thomson system.

In addition, the fishway will enable fish to access over 85km of upstream habitat. Work to re-create this amount of habitat from scratch would cost well over $4 million and many years to complete.

Where will the walking track go?

Just as the fish are getting a helping hand around the bend, walkers will too. New interpretative signage and improved walking tracks, designed in collaboration with the community, will encourage even more visitors to connect with Horseshoe Bend’s cultural past.

Constructing a fishway will require the upgrade and realignment of some sections of the current walking track that provides access to the area. We have been working with Department of Environment, Land, Planning and Water (DELWP) staff to develop a plan for the track and area that allows visitors to take in the ruggedness of the site. As a result, the track location has been through a number of iterations.

There will be no change to the track alignment or accessibility from the carpark to the river and from the river to the tunnel exit. The track alignment to the tunnel entry is now likely to incorporate two natural crossing points at suitable locations allowing visitors to safely continue to enjoy the heritage area.

Will the walking track to the inlet and outlet of the tunnel be accessible all year round?

Like the current route to the inlet, the new track will be open all year round. Currently during high flows, caused by heavy rainfall it can be difficult or unsafe to access the inlet. This will continue to be the case with the new track. For more information on the walking track see the question and answer above.

Where will the excavated rock go?

Based on the current design, we estimate up to 3500m3 of rock may need to be relocated. This estimate is at the upper end of the predicted volume. By comparison the construction of the tunnel resulted in 13,600 m3 of rock being dug out and deposited in the river.

Importantly, the fishway is to be blended into the bedrock and the excavated material will remain onsite but will not impact on heritage sites that have been identified as part of a comprehensive heritage assessment (part one and part two).

The intent is to leave this rock onsite and landscape it to blend in with the natural features of the inner bends of the river. Natural processes will also ensure that it will regenerate over time. Based on the natural regeneration in other project areas, we estimate this will take approximately five years.

Options to move excavated rock off-site were explored however the impact to the area would be significant. It would require extensive widening of the access track, particularly at the sharp bends. The decisions to enable more water to go through the tunnel and to avoid any damage to the culturally significant rock bar has influenced the amount of rock that needs to be relocated.

Does an environmental effects statement need to be completed?

No. We have reviewed the requirements for Ministerial Guidelines for Environmental Effects under the Environment Effects Act 1978. According to these guidelines this project is neither the size nor scale to trigger an EES. However, we are working closely with DELWP to ensure all permits and approvals are in place before construction.

A preliminary Environmental Management Plan has been developed and this will be complemented by a Construction Environmental Management Plan. Studies and reports have been prepared and we believe these go well beyond any requirements set out by an EES.

The project also does not require an EPBC Act referral as per the guidelines and as advised by the Department of Environment and Energy.

Will the track be widened and what about tree removal?

There will be some impacts to the surrounding area. Full rehabilitation of the site post construction is a priority for us.

The access track is currently two metres wide and will be temporarily widened where required to a maximum of one metre on either side, and then narrowed back to two metres at the end of the project. Vegetation disturbance will be conducted as approved by Baw Baw Shire Council and the area will be rehabilitated in accordance with a Construction Environmental Management Plan which will have stringent conditions within it that contractors will need to comply with.

Our staff have been conducting photo point monitoring over the last two years to watch how the bush regenerates and changes. You can view some of the photos taken from this monitoring over the last two years. We expect the trees, shrubs and ground covers to fully regenerate within the areas that will be temporarily disturbed. An offset will be established as part of the vegetation removal.

The vegetation removed during the project will result in more than double the benefit to the environment. How?

Vegetation offsets require that for every 1 hectare of vegetation removed, more than 1 hectare of similar vegetation is protected forever against clearing. The site at Horseshoe Bend will also be rehabilitated to a similar condition to its current state, meaning any vegetation removal will be temporary and the site will regenerate.  We have estimated the off-set cost will be $70,000.

We have the appropriate native vegetation removal permits to allow this work to happen.

What if the fishway needs maintenance or repair?

We are committed to ensuring the fishway is a success and will be undertaking repair work in the unlikely event it is damaged during floods. The correct functioning of the fishway is significant to the survival of the Australian Grayling population in the Thomson River. To achieve this ongoing monitoring and maintenance will be required. When repair is needed it will be done by hand or using small scale equipment.

Will the fishway fill with sediment?

During times of high flows rivers become more active and sediment is transported downstream. In a flood, the speed of the flowing water picks up sediments and when water movement slows, sediments deposit again. In the upper Thomson River, sediments typically move from one bend in the river to the next; in other words, sediment deposits chase each other downstream.

We expect some sediment to be deposited on the fishway, but it has been designed to mimic the natural system. During high flow events sediment deposits will be picked up and transported downstream just as they do in the rest of the river system.  If large flooding does impact the fishway, we will complete maintenance by hand or using small scale equipment.

Could the river be damaged by this work?

The Thomson River has heritage status under the Heritage Rivers Act. We have worked through the vast array of environmental and heritage issues with the steering committee over the last two years and understand that this is a delicate operation.

The act identifies “Heritage Rivers Areas” and “Natural Catchment Areas” and outlines activities that are not permitted within heritage river areas (section 10). The Thomson River at Horseshoe Bend is included in the Thomson River Heritage Area. The proposed activities do no breach any conditions listed in the Act.

The tender and construction phases of this project will be governed by strict legislative requirements and standards will be mandated and clearly defined in the technical specifications. Through the procurement process, a contractor will be selected based on their ability to comply with these requirements. We will be looking for potential contractors to demonstrate this through past performance with documented examples and undertaking reference checks to ensure systems and processes have been routinely, consistently and successfully applied and followed in similar settings or for similar types of work.

In addition, there will be a site superintendent on site daily during construction to supervise the works. The superintendent will also approve defined hold points in the construction program from pre-planning approval, set outs and test area.

What about the EBPC Act?

Section 18(4) of the act says that “a person must not take an action that has, will, or is likely to have a significant impact on a listed threatened species.” As part of the project, we sought legal advice and advice from the Department of Environment and Energy (the statutory authority for EPBC)

As the construction of a fishway at Horseshoe Bend will have a positive impact on EPBC listed species such as Australian Grayling by increasing the amount of habitat available, and there are no other apparent risks to EPBC species, a referral is not required.

Have you considered the possibility of mercury becoming mobile when the fishway is created?

Yes – we have. When this concern was first raised with us we contacted an independent expert to undertake mercury testing. They tested 18 sites and found that mercury levels detected are not a concern for humans or animals. To be sure these results could be relied upon, we then had a second mercury expert independently review the results and testing process. Recent criticisms have been levelled that testing should have included drilling to three metres into the bedrock. Both experts involved in the mercury testing have said this is unnecessary.

The Construction Environmental Management Plan being developed will contain protocols to manage all site-based risks. The protocols will include monitoring, assessing, and management actions to ensure the safety of the contractors, environment, and community.

The project to permanently re-connect the Thomson River has had rigorous planning, design and review. All the necessary permits are now in place for the fishway creation to begin.

Project timelines

Extensive consultation has been carried out to ensure the fishway balances the significant heritage and cultural values of the site with the environmental improvement objectives.

We have secured all necessary permits to allow the project to begin. We expect to begin a tender process mid 2018 and the creation of the fishway to occur during 2019.

The tender process will be done in accordance with Government requirements for public tendering.