Improve Fish Passage

These measures deal with impacts to fish movement within estuaries and rivers. Structures to facilitate fish passage will not always deal with other problems caused by in-channel structures, particularly impoundment, sedimentation upstream of structures and disruption to sediment transport processes downstream. The optimal solution for restoring all aspects of functionality including fish passage is weir removal (and for some structures, modification). This option should be investigated first and implemented where practicable. Where removal or modification of structures is not possible the following measures might be appropriate. It is worth noting that where structures can be removed, other measures to improve habitat upstream and downstream should be undertaken after the flow and sediment regime have had time to adjust.

A range of in-channel structures can be designed to facilitate the upstream and downstream movement of fish and other aquatic fauna within river systems. Fish passes can be applied to watercourses where natural or human placed obstructions such as dams, weirs, or culverts prevent or interfere with fish migration. The type of fish pass needed to maximise fish passage will depend upon the site conditions and the species requirements within the river system.

Artificial, substitutes for river channels can be designed around barriers to fish passage. Such artificial river channels normally have a low gradient and extend from below the obstruction to a considerable distance upstream.

Structures at the confluence between tidal rivers and estuaries or the coast such as sluices and barrages can prevent fish passage. Operational changes and improved design of new structures can improve the potential for fish migration.

Pumping station intakes can prevent fish passage by entraining fish, causing damage or mortality. Structures can be designed (i.e. screens) to prevent the intake of fish by pumping stations or other structures which extract from the water environment.