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.

Quick facts

Disclaimer

In addition to the standard disclaimer located at the bottom of the page, please note the Fishways (biopassage structures) disclaimer.

For practical reasons

the addition of new features to existing barriers is the most common strategy for enhancing biopassage.

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[1] 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

• All biopassage structures (e.g. fishways and fish-friendly culverts) require water to operate, and the hydrological design criteria for passage (i.e. the river flows that facilitate operation of the fishway) need to be carefully considered prior to any design
• The entrance location (i.e. where fish enter the structure, typically at the downstream end) and water discharge need to attract fish, otherwise fish will not find the fishway. The location and hydraulic conditions of a fishway entrance are site-specific and critical to the structure’s ability to attract fish (also called attraction flow)
• Generally, smaller species or earlier life stages are weaker swimmers than larger species or later life stages, and water velocity, together with zero velocity resting areas, within a structure need to be kept relatively low if the smaller fish are to pass
• Structures also need to allow for movement of the largest fish in the local site-specific fish community, in terms of slot widths, dimensions of pools, channels and/or chambers, and spaces in trash rack
• Fish community composition including species, sizes, behaviours, life history stages and migration requirements are a crucial consideration for effective passage, and this should be considered at the design phase, and all structures should be monitored to determine effectiveness
• All structures require regular maintenance, particularly following flood events.

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[2].

Biopassage structures

Most biopassage structures in Queensland are currently designed for fish and include the following types:

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References

1. ^ Moore, M & McCann, J (2018), Sunshine Coast Council Fish Barrier Prioritisation. [online], Catchment Solutions. Available at: https://catchmentsolutions.com.au/rc-services/fisheries-aquatic-ecosystems/?post_type=resources.
2. ^ O'Connor, J, Stuart, I, Jones, M & Arthur Rylah Institute for Environmental Research (2017), Guidelines for the design, approval and construction of fishways. [online] Available at: http://nla.gov.au/nla.obj-664261559 [Accessed 25 February 2021].

Last updated: 10 May 2021