What is a waterway barrier work?
Free movement along waterways and onto floodplains is an essential requirement for the survival and productivity of many species of Queensland fish. Many species must move into different habitats for breeding or rearing of young, or to access critical habitats for food and protection. Movement occurs within and between inland rivers and creeks, and also along coastal streams throughout adult, juvenile and larval stages. Some fish move between fresh and salt water for access to feeding and breeding habitats. Some species migrate large distances through both marine and riverine environments.
Thousands of instream structures such as dams, weirs, floodgates and culverts have been built on waterways in Queensland. In many cases fish are unable to move into waters upstream or downstream of these barriers. This loss of access to habitat has caused a decline in distribution of native fish populations, including species of commercial, recreational and traditional importance (barramundi, mullet and Australian bass). In Australia, declines of inland species such as Murray cod, freshwater catfish and silver perch are thought to be largely due to the impacts of barriers to fish movement.
Development of new, or raising of existing waterway barriers, must therefore provide adequate fish passage.
Examples of waterway barrier works
As well as dams and weirs, the following are examples of developments may be waterway barrier works and could be undertaken under a development approval under the Planning Act 2016 or in compliance with the Accepted Development Requirements for operational works that is the construction or raising of waterway barrier works:
- Culverts including pipe, arch and box culverts when they occur in waterways.
- Bridges with instream components that block the low flow channel and/or reduce the cross-sectional area of the waterway. See ‘What is not a waterway barrier work’ fact sheet for examples of bridge works that are not waterway barrier works.
- Bed level crossings may be in sections of access roads to agricultural or forestry land, or to overland or underground infrastructure. They are usually made by compacting natural dirt, using imported or local rocks, or concrete. If not constructed properly, they can hinder fish passage on low to medium flows due to head loss differences. They can also hinder fish passage due to increased velocities caused by the smooth surface finish at concrete crossings.
- Causeways are waterway crossings constructed above the stream bed. The purpose is to provide a safe water crossing. They create a thin sheet of water flow passing rapidly over the surface and a head loss at the downstream end, both of which act as barriers to fish movement, particularly at lower flows.
- Tidal or flood gates are built across waterways to stop the flow of water in a particular direction (e.g. to prevent salt water intrusion or flooding). They generally contain a gate that closes when the downstream water level rises, stopping salt water or flood water moving through to the other side. Fish movement only occurs through the flood or tidal gate when the gate is open.
- Partial bunds such as temporary instream platforms for bridge construction, recduce the cross-sectional area of a water, which increases velocities and turbulence, which in turn affects fish movement. The impact of a partial bund on fish movement can be minimised when:
- the bund does not constrict the area or flows of a low flow channel;
- the works are temporary; and/or
- all work will be completed (and the bund removed) during low flows when the flow will be contained wholly within a low flow channel.
- Temporary waterway barriers are constructed for a variety of reasons, and these also have the potential to cause adverse impacts to native fish stocks. While the temporary nature of these barriers reduces their long term impact on fish stocks, they may restrict important fish movements at a critical stage of the spawning cycle, or interrupt other migratory patterns.
- Silt curtains are made of fine material to stop the movement of silt and sediment. Where the curtains are fixed across the waterway they impede fish passage.
- Netting and screens, either temporary or permanent, may be installed across waterways to prevent intrusion of predators such as crocodiles and sharks. Netting may prevent other fish movement depending on the mesh size. Lack of maintenance may result in build up of debris which effectively decreases the mesh size. Screens have been employed on some residential canal lake intakes to prevent large debris (and sharks) from entering the waterways. Fish that are able to pass through the screens or nets as juveniles may have difficulties returning through them as adults.
- Levee banks across a waterway: Levees built across tributaries connecting floodplain wetlands to streams are waterway barriers. The main reason for the construction of levee banks is to stop flood water or tidal water moving into floodplains or low lying areas, which are often the site of human habitation or agriculture. In doing so levees also cut off access from the main river system to floodplain wetlands, which are used by fish for feeding, breeding and as nursery grounds.
- Litter booms are floating booms that trap litter. They allow fish movement beneath the float, but as litter gradually accumulates behind these structures, they create significant shading; and the build up of debris inhibits fish passage for species which use the top of the water column (e.g. sea mullet (Mugil cephalus) and snub-nosed garfish (Arrhamphus sclerolepis krefftii)). Regular maintenance will ensure fish passage is provided.
- Trash racks skim rubbish and debris floating on the water to reduce pollution in waterways. Unlike litter booms, trash racks are generally fixed structures, such as grills, bags or cages. If the mesh or grill aperture is too small or narrow for certain fish, trash racks impact on fish movement, even if they are maintained regularly. The negative impact on fish movement increases as the amount of trash increases.
- Riffle structures are small rock weirs constructed across a waterway for infrastructure protection, erosion and sediment control, or water quality improvement. Such structures create fish movement barriers until the water level rises above the structure on both sides (drownout).
- Revetment wall and abutment works are sometimes carried out to prevent bank erosion. These have the potential to impede fish passage by narrowing waterways and increasing water velocities. Please see the ‘What is not a waterway barrier work’ factsheet for examples of revetment wall and abutment works that are not waterway barrier works
- Rock and grass chutes are used to prevent the progress of head-cut erosion upstream. The placement of these chutes is critical to prevent fish passage problems.
- Retro-fitting fishways to existing barriers are waterway barrier works and all designs must be approved via Development Approval. A fishway professional must also verify that the designs will provide for adequate fish passage.
- Structural adjustments and repairs to existing waterway barriers are generally considered maintenance works, but they have the potential to impact on fish movement. For example:
- Scour protection
- Culvert replacement
- Retrofitting culvert inverts and culvert lining
- Apron repair and installation
- End wall and wing wall replacement.
Some forms of the works or structures mentioned above may not be considered to be waterway barriers if they are designed and constructed to ensure fish passage is not impacted upon. Refer to Fact Sheet: What is not a waterway barrier work for more details for when this applies.