Biopassage structures (fishways)
Biopassage structures (e.g. fishways (fish ladders) and fish-friendly culverts) can be constructed to help provide adequate movement of fish and other aquatic fauna past large waterway barriers (e.g. dams, weirs, and tidal barriers/bunds). Smaller barriers such as culverts and road crossings can also be enhanced for biopassage using simple modifications such as rock ramps.
Information about biopassage structures for Queensland can be found on WetlandMaps.
The design of structures to assist biopassage has evolved over time. Many initial designs were based on northern hemisphere fishways that were designed for stronger, larger, adult fish such as Atlantic salmon (e.g. pool and weir fishways or fish ladders). Many Australian fish species migrate as juveniles and do not possess the strength to ascend fish passage structures that may be designed for adult stronger fish. Without designs that are specific to the local fish populations that need to move, fish passage structures run the risk of becoming barriers instead.
Biopassage structures tend to be engineered for larger barriers such as weirs or dams, and include structures such as fish lifts (mechanical designs) or vertical slot fishways. Other fish passage structures in Queensland are designed for barriers under 4 metres in height including rock ramps, cones, bypass channels or enhancing culverts to be fish-friendly (e.g. by adding baffles). Even small enhancements to barriers can make a significant difference.
The removal of artificial instream barriers is another option for providing passage by restoring connectivity. It involves reinstating an open channel, allowing all species and size classes of fish to move at all flows.
Principles for effective passage
A strong discharge of water from a fishway is a key factor in attracting fish. Many fishways discharge only a small percentage of river flow. For example, most Murray River fishways discharge less than 1% of the water flowing past the weir, therefore rather than relying on discharge measurements, these structures also need to specify a minimum head loss and resulting water velocity at the entrance. The head loss ensures there is adequate attraction of fish to the structure at high tailwater levels. For adequate fishway operation, water releases should first be directed down the fishway until the fishway reaches the design discharge volume, after which outlet releases and spillway flow should be optimised to create attraction flows for fish.
Most biopassage structures in Queensland are currently designed for fish and include the following types:
Rock ramp fishways
Vertical slot fishways
Pool and weir fishways
Removal of barriers
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Last updated: 10 May 2021
This page should be cited as:
Department of Environment and Science, Queensland (2021) Biopassage structures (fishways), WetlandInfo website, accessed 30 August 2021. Available at: https://wetlandinfo.des.qld.gov.au/wetlands/management/fish-passage/technologies/