Management of barriers and instream structures

Identifying barriers

When deciding how barriers are identified and assessed for remediation, there are a number of considerations:

• the variable nature of aquatic fauna behaviour
• swimming ability
• habitat requirements
• local land use
• water regimes.

When managing aquatic fauna biopassage (biopassage), barriers must first be identified and located. Surrounding aquatic habitats also need to be evaluated to increase understanding of habitat requirements for local populations of fish and other aquatic fauna (e.g. turtles, platypus and freshwater shrimp). For example, in a coastal catchment, the proximity of the barrier to estuarine waters should be considered, as it is an important requirement for diadromous species[2]. Whereas in intermittent river systems accessibility to or distance from known refuges is important[1].

Barriers may influence biopassage by affecting[2]:

• water surface drop - vertical drop between the barrier and the bed of the waterway, such as road crossings, weirs, and culvert aprons
• velocity - speed of water related to fish swimming capabilities and ability to pass the barrier
• turbulence - fluctuating water velocities and pressures, which are generally an issue during medium to high flow conditions downstream of the barrier
• water depth - shallow water, particularly during low flow conditions

• light conditions - darkness, shadows, shading, and other altered light conditions inside culverts/pipes, particularly under low-flow conditions, may affect aquatic fauna behaviour

Other barriers may include:

• chemistry/temperature - low dissolved oxygen, acid sulphate soil discharge, temperature fluctuations and cold water (e.g. deep water in dams), and other potential contaminants
• weeds and vegetation- physical blockage of waterway from aquatic weeds such as typha, hymenachne and salvinia.[2]

Barriers can be temporary (e.g. such as a silt curtain, or a sand dam) or permanent (e.g. large water supply dam).

Prioritisation of barriers

Prioritising barriers for management in a catchment is a key process for determinating which biopassage remediation is required. There are many barriers, some natural, and others constructed for essential reasons i.e. water supply and roads. Prioritising barriers according to the level of impact and exploring remediation methods can inform future management actions.

There are different methods for prioritising barriers for management action. All methods need to identify barriers in the study area. This can be achieved, for example, through creating an inventory. This step can be undertaken through rapid desktop assessments to identify which structures need to be assessed in the field. As more development occurs in the study area, or as barriers are remediated, this inventory will change over time.

The list of barriers is usually scored against criteria specific to the study area, to identify the highest priority barriers (in terms of impacts to biopassage) and may also include economic and social considerations. Remediation options need to be carefully considered, including costs and benefits of modifications and potential removal. The suitability of any remediation option, such as installing a fishway (e.g. fish ladder), needs to suit the local aquatic species.

Considerations for barrier scoring and prioritisation, based on work undertaken for fish in Queensland, include:

• area of habitat upstream
• stream order
• catchment condition
• proximity to the coast/estuary
• water flow regime, refugia
• riparian vegetation condition
• conservation significance (fish species)
• fisheries productivity or economic benefits of remediation
• barrier type and passability
• community support
• estimated cost (of remediation).

The scoring of barriers against criteria, such as the ones above, can provide an informed list of prioritised barriers for remediation to improve biopassage.

Additional information

• Guidelines for conducting an inventory of instream structures in coastal Queensland
• Inventory of Instream Structures Impacting on Ramsar Wetlands
• Fish Barrier Prioritisation (Landscape Scale Coastal, no economic analysis)
• Fish Barrier Prioritisation (Landscape Scale Coastal, with economic analysis)
• Fish Barrier Prioritisation (Protected areas)
• Fish Barrier Prioritisation (Wetland/Offstream)
• RIver flow regulation, fish BEhaviour and Status, is funded under the European Union Horizon 2020 Research and Innovation Programme. This site includes links to research to address and understand freshwater species and movement in altered inland aquatic habitats.

References

1. ^ Marshall, J & Lobegeiger, J (July 2020), Fish drought risk in the Queensland Murray-Darling Basin, A report to support Queensland Government proposals for Toolkit Measures Projects in the northern Murray Darling Basin.
2. ^ a b c 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.

Last updated: 10 May 2021