Australian researchers have come up with an ingenious tube system to get fish up and over those dam walls.
A team of engineers at UNSW Sydney has created a ‘tube fishway’ that allows fish to glide past dam walls, weirs and other river barriers that block their migration in Australian rivers.
The low-cost and low-energy installation works by pumping fish at high velocity — protected by a cushion of water — through a tube running over the obstructing barrier to deliver them safely into the water on the other side.
Tube fishways have the potential to reconnect populations of fish throughout Australia, or anywhere in the world, where barriers such as dams and weirs in rivers are believed to be linked to a massive decline of freshwater fish stocks over the past half century.
The first comprehensive global report on the status of freshwater migratory fish released in July 2020 found that species have plummeted by 76 percent on average between 1970 and 2016 — a higher rate of decline than both marine and terrestrial migratory species.
In Australia, waterways are already suffering mass fish death events due to dry conditions, bushfire runoff, sudden changes in water quality following rain, algal blooms and sudden temperature drops.
Professor Richard Kingsford, director of the Centre for Ecosystem Science, from UNSW School of Biological, Earth and Environmental Sciences, says dams, weirs and other river barriers have disrupted fish reproduction cycles, as many river fish are prevented from migrating to spawn.
“Just in the Murray-Darling Basin rivers alone, there are 10,000 barriers of all kinds throughout the river system which have contributed to native fish numbers declining by 90 per cent. If we could reconnect our rivers and give fish the ability to navigate our rivers safely, we would see more breeding and healthier native fish populations in our rivers,” he said.
It’s a problem that Australian scientists have been trying to solve for more than a century, with a number of types of fishways constructed to help fish to navigate past barriers. They have generally been found too expensive to install and maintain, with some larger systems often failing to adequately do the job.
UNSW Engineering’s adjunct professor Bill Peirson was one of the scientists who built and tested a prototype of the tube fishway at Manly Vale.
“A key issue is attracting fish into a pipe so that we can move them up the slope with the new fishway,” he said.
In order to test the prototype, Peirson and his colleague Dr Stefan Felder connected two large tanks with two pipes that pumped water to and fro. In the tank at the bottom of the slope, a small Australian bass fish was coaxed into a chamber before being propelled at high speed in oxygenated water through a Perspex tube into a tank further up the slope — some eight metres higher in elevation.
“Dr Harris showed that with appropriate geometries, fish can be reliably attracted into the chamber. The beauty of the design is that it uses the energy available from the reservoir above to then lift the fish,” Peirson said.
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In a commercial setting, installations of the tube fishway would use connecting tubes considerably larger than the 90 mm one used in the prototype.
“Our numerical modelling work shows that this system will work reliably for pipes at least one metre in diameter, lifting fish more than 100 m vertically. This is potentially a game changer in the ecological management of large dams,” he said.
The solution designed by Peirson and Harris is relatively inexpensive, easily adaptable to the local environment, and leaves only a small carbon footprint.
Peirson said that the challenge that his team is looking to address is getting the fish downstream in the river.
“This is not important for small structures — they just swim down with the flow. However, for high structures they can be killed by impacts in the overflow and we need to find gentler ways for them to descend large dams,” he said.
The researchers are looking for opportunities to implement the tube fishway in a commercial installation and are currently in talks with Parramatta City Council about the potential to install one at Parramatta’s Marsden St Weir, which will allow wild fish to move upstream.
“Many of our weirs are very old — created to provide water supplies during Australia’s long droughts. It is exciting to think that within the next few years, wild fish might be able to migrate along a river for the first time in more than a century,” he said.
Another important step as they translate the design into the real world will be ensuring that original river structures are not diminished while promoting the health of the fish stocks using these waterways.
“There’s no reason why we can’t have dams and healthy river systems at the same time,” he added.