Cheap tube for flinging fish
Engineers have come up with a fish transport system that lets them glide over dam walls, weirs and other barriers.
The ‘tube fishway’ is a low-cost and low-energy installation that 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 – and potentially the world – where barriers like dams and weirs in rivers are believed to be linked to a massive decline of freshwater fish stocks over the past half century.
“Freshwater fish populations have declined by more than 80 per cent over the last four decades across the globe. This is partly due to the hundreds of thousands of our dams, weirs and barriers stopping their movements,” says Professor Richard Kingsford, Director of the Centre for Ecosystem Science, from UNSW School of Biological, Earth and Environmental Sciences.
“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.”
Engineers and scientists have grappled with the problem for more than a century, constructing many different types of fishways. But these are expensive to install and maintain, while even some of the largest devices have failed to adequately do the job.
But UNSW scientists and engineers have come up with a relatively inexpensive solution, easily adaptable to the local environment and leaving only a small carbon footprint.
At a demonstration site in Manly Vale, two large tanks have been set up, each connected by two pipes that pump water to and fro.
In the tank at the bottom of a slope, fish are coaxed into a chamber before being propelled at high speed in oxygenated water through a PVC tube into a tank further up the slope – climbing a whole eight metres higher in elevation.
The beauty of the design is that it uses the energy available from the reservoir above to lift the fish.
In a commercial setting, installations of the tube fishway would use connecting tubes considerably larger than the 90mm one used in the prototype.
Computer modelling suggests the UNSW system will work reliably for pipes at least one metre in diameter, lifting fish more than 100 metres vertically.
The research group is currently in talks with Parramatta City Council about the potential to install a fishway at Parramatta’s Marsden St Weir – to allow wild fish to move upstream.
A demonstration can be seen below.