Australian governments spend millions of dollars to conserve aquatic biodiversity and fisheries threatened by water-resource development, but outcomes are poor when dams or weirs block fish migrations. Migrations essential for fish biodiversity, productivity and viability are obstructed by tens of thousands of barriers. Existing high fishways are unsatisfactory.
Current approaches using fishways, locks and lifts vary in their success but all are costly. For example, the fish lift on Tallowa Dam on the Shoalhaven River cost $48 million. The UNSW Tube Fishway Project is developing cost-effective techniques to provide fish passage over high (>8m) barriers, with considerable promise for more ambitious applications.
There are two key elements: fish attraction into a pipe chamber and safe fish transport through a vertical riser. The attraction design concept involves applying existing fishways’ knowledge to attract free-swimming fish into a chamber. The transport process utilizes the acceleration of flows in the tube system to move the chamber contents, with the fish, vertically through a riser pipe at near atmospheric pressure and over the dam wall.
A one-third-scale physical attraction model has been constructed and tested. It consists of an initial collection bay that leads through a slide gate into a trap within a cylindrical transfer chamber. This chamber, which ends in a conical section leading into the exit pipe, can be sealed and pressurized, enabling transfers.
The effectiveness of this approach was demonstrated using experimental groups of young Australian bass (~50mm) and rainbow trout (~180mm) (Harris et al., 2019). Four variations of the design were trialled from 2014 to 2017. The final series of nine experimental trials with bass in August 2017 resulted in a 98% rate of successful passage within the brief period allowed for each operating cycle. No injuries or mortalities were recorded among experimental fish over the following two weeks.
In parallel, a novel pumping method was demonstrated at the Water Research Laboratory using physical models with vertical lifts of 1, 4 and 8 metres. Using a system of simple conduits and a sequence of valve openings, water can be transported from an attraction chamber at the foot of a dam structure over its crest. Unsteady flow contributes significantly to the volume of water lifted. The volume lifted remains in proximity to atmospheric pressure during transport and delivery. Hydrodynamic test with sensor fish and image processing techniques documented the shear stresses while live fish (Australian Bass and Silver Perch) were successfully lifted to 4 and 8 m elevations without injury or mortality of fish. Numerical predictions indicate safe transport of fish over vertical distances in excess of 100m by controlling the turbulence generated during the transport process.
Harris, J H, Peirson, W L, Mefford B, Kingsford, R T and Felder, S (2019) Pumping fish upstream over dams: an innovative pump fishway concept. J. Ecohydraulics, published online 04/11/2019.
The Gayini wetland is part of the Lowbidgee floodplain, the largest remaining area of wetlands in the Murrumbidgee Valley, with Yanga National Park, within the southern Murray-Darling Basin.
Ensuring freshwater security within Australia’s Murray-Darling Basin (MDB) is one of Australia’s greatest natural resource management challenges, involving complex ecological and sociological processes and decision-making.