Australia is characterised by rivers with highly variable hydrology and a freshwater fish fauna where potamodromy and diadromy are common. These migrations involve a wide size range of fish from 20 mm to 1500mm, with a correspondingly wide range of swimming abilities. Acknowledging that designing fishways to pass these fish is a significant challenge the Murray Darling Basin Authority invested in research over 10 years to improve designs.
Variations in the vertical-slot design were assessed with CFD and tested in the field. Roughened baffles and roughened walls provided promising hydraulics, but did not improve fish passage in the field. However, the ‘control’, which only reduced discharge through the fishway by changing the profile of the slot, greatly improved fish passage. The finding that turbulence within the entire fishway pool was critical, and could be easily manipulated, has led to a suite of vertical-slot baffle profiles to suit different hydrologies and fish assemblages. Site-specific slot shapes are now a standard design input for vertical-slot fishways.
Experiments were also conducted on small Denil fishways, which showed passage of small fish (20-50 mm in length) was very poor, despite earlier studies demonstrating they could effectively pass small herring (50-100 mm). Broader findings on ecology have also led to separation of ecological and hydrological function in fishway design, where small and large fish passage have been separated, and high and low flow fish passage accommodated differently. The research benefited from a multi-state interaction of scientists working on the one program, which generated ideas, ensured robust science, and distributed the findings. Importantly, the program applied the principles of adaptive management and new learnings were rapidly incorporated into new fishway designs.