Snowy Hydro Secondary Controls

Fish screens are physical barriers strategically placed in waterways to enable water passage while effectively preventing fish from being entrained into man-made structures like irrigation channels and hydropower schemes. Snowy 2.0 is a 2000 MW pumped hydropower scheme that introduces a risk of transferring pest fish. Fish screens are an option proposed to prevent the spread of pest fish, including eggs, larvae, juveniles and adults.

The challenge

Snowy Hydro Limited (SHL) is constructing a 2000 MW pumped hydropower facility (Snowy 2.0) to augment the capacity of the existing Snowy Mountains Scheme in south-eastern NSW. Snowy 2.0 will link Talbingo (the lower) and Tantangara (the upper) reservoirs through a pipeline and pumped hydro-electric power station.

During the pumping phase of operations, Snowy 2.0 will transfer water from Talbingo Reservoir to Tantangara Reservoir, and during the generation phase, water will be transferred in the opposite direction. This introduces a risk of transferring pest fish such as redfin perch (Perca fluviatilis), into Tantangara Reservoir and then to Lake Eucumbene and the upper Murrumbidgee River, where they are currently considered absent.

The Conditions of Approval for Snowy 2.0 require SHL to install fish screens in Tantangara Reservoir to prevent, so far as is reasonably practicable, the spread of pest fish (primarily redfin in all its forms: eggs, larvae, juveniles and adults).

Project name:
Snowy Hydro Secondary Controls: Redfin trials
Funding: Snowy Hydro Limited $210,160

Our response

The objective was to assess the relative effectiveness of screens to prevent fish transfer. The permeability of screens can be assessed using a laboratory flume to test the smallest and most vulnerable life-stages of redfin (eggs and larvae) and provide a tool to guide screen design for Snowy 2.0.

The result

Our main objective was to provide estimates of the relative entrainment rates of egg (5 DPF) and larval life-stages of redfin (up to 34 DPH) for four wedge-wire mesh aperture sizes (0.25 mm, 0.5 mm, 0.75 mm, and 1 mm) and three approach velocities (0.03, 0.075 and 0.15 m/s) using a series of laboratory flume experiments. The results found that some level of entrainment was possible through all apertures tested up to an age of between 10 and 34 DPH depending on the screen aperture size.

For a given screen aperture, entrainment increased with increasing velocity but decreased with redfin age. The zero velocity trials also enabled fish to approach and pass through the screens under their own volition. The greatest entrainment probability exists for the earliest life-stages, including pre-hatch eggs (9–11 days DPF) and larvae < 20 DPH, as these are 1) the smallest sized fish, 2) lack fully-developed bony structures and can compress through screens (with or without velocity), 3) are relatively poor swimmers and 4) may actively drift with the water velocity, either because their locomotory systems are not fully developed or they are choosing to drift with the current for dispersal.

While no screen was 100% effective for all life stages of redfin, our study found several factors that reduced entrainment. The smaller screen apertures tested (0.25 and 0.5 mm) led to a combination of reduced larval entrainment rates and less life-stages of redfin entrained. The present study also found that lowering the approach velocity to within or below the swimming ability of the redfin larvae may enable fish to choose to avoid the screen but could also reduce the ability of the water velocity to transport the larvae towards- (impingement), and potentially through- (entrainment), the screen.

Our team

Principal scientist

portrait of Professor Lee Baumgartner
Professor Lee Baumgartner
Professor of Fisheries and River Management
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Our research team

portrait of Joachim Bretzel
Joachim Bretzel
PhD Candidate
portrait of Dr Katie Doyle
Dr Katie Doyle
Fisheries and hydopower scientist
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portrait of Dr Ben Fanson
Dr Ben Fanson
Biometrician, Arthur Rylah Institute
portrait of Dr Martin Mallen-Cooper
Dr Martin Mallen-Cooper
Fish ecology and fish passage
portrait of Cameron McGregor
Cameron McGregor
Research officer
portrait of Dr Nathan Ning
Dr Nathan Ning
Aquatic ecologist
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portrait of Dr Lalantha Senevirathna
Dr Lalantha Senevirathna
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portrait of Associate Professor Ivor Stuart
Associate Professor Ivor Stuart
Fisheries ecologist
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portrait of Associate Professor Peter Thew
Associate Professor Peter Thew
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portrait of Kelly Thomas
Kelly Thomas
Technical officer
portrait of Dr An Vu Vi
Dr An Vu Vi
Freshwater fish ecologist
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Key research publications

Doyle, K., Stuart, I., Ning, N., Vu, A. V., Zarski, D., Thomas, K., McGregor, C., Bretzel, J., Mallen-Cooper, M., Fanson, B. G., Thew, P., Senevirathna, L., & Baumgartner, L. J. (2023). Redfin Larvae Screen Entrainment Study: Research Commissioned by Snowy Hydro Limited. (1 ed.).

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