Barriers like dam walls and weirs stop fish migrating in our rivers, but scientists at UNSW Sydney have invented a creative way to get around - or over - the problem.
Known as the "fish tubeway", the inexpensive and energy-efficient solution works by literally pumping fish through a high-speed tube. Protected by a cushion of water, they go up and over the dam, arriving safely on the other side.
A prototype of the invention was shown off at the UNSW Water Research Laboratory in Manly Vale recently. Now the scientists are in talks with Parramatta City Council in Sydney about the possibility of installing one on Darug country at the Marsden St Weir.
Tube fishways could reconnect populations of fish throughout Australia – and potentially the world. The massive decline of freshwater fish stocks over the last century is believed to be linked to barriers like dams and weirs in rivers.
Director of the Centre for Ecosystem Science, UNSW's Professor Richard Kingsford, said river barriers have stopped fish migrating to spawn, disrupting disrupted fish reproduction cycles.
"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," said Professor Kingsford.
"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."
For more than 100 years, scientists and engineers have been working on this problem. Many different types of fishways have been made, helping fish to navigate past barriers. But these are expensive to install and maintain, and that's if they can even do the job.
This latest solution was made with this in mind - aiming for a relatively inexpensive, easily adaptable solution that would leave a small carbon footprint.
Using an idea from UNSW's Centre for Ecosystem Science's Associate Professor John Harris, UNSW Engineering's Adjunct Professor Bill Peirson and Dr Stefan Felder developed, built and tested a prototype of the tube fishway on Gayemagal land in Manly Vale.
How it works
Two large tanks - one at the top of a slope, the other at the bottom - were connected by two pipes that pumped water backwards and forwards. In the tank at the bottom of the hill, 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 – a whole eight metres higher in elevation.
"A key issue is attracting fish into a pipe so that we can move them up the slope with the new fishway," Professor Peirson says.
"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."
The tubes in the prototype were 90mm in diameter.
"Our numerical modelling work shows that this system will work reliably for pipes at least one metre in diameter, lifting fish more than 100m vertically. This is potentially a game-changer in the ecological management of large dams," said Professor Peirson.
"A challenge that we are just commencing 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."
The group spoke with Parramatta City Council about installing a fish tubeway at Marsden St Weir, which would mean wild fish could 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," said Professor Peirson.
Some of the group's challenges as they move from the laboratory into the field include making sure the changes cause no further damage to the river.
"There's no reason why we can't have dams and healthy river systems at the same time," said Professor Peirson.
"Any fishway must not compromise the safety of the weir or dam. The fishway must also demonstrate that it can operate reliably before and after the very powerful floods we have here in Australia.
"Dams are important for maintaining our water supplies during droughts, but they greatly disrupt our river systems. There is now real prospect that we can allow fish to migrate as they should and significantly restore our river ecosystems."