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Fish passage

Weirs/Dams

The use of on-line weirs and dams is discouraged in the Auckland Region, due to their impacts on hydrology and fish populations. However there are still many historic structures present throughout the region that require retrofitting in order to make them compliant with fish passage regulations.

Issues

The most common fish passage problems associated with weirs and dams are:

Weir featuring a vertical cascade, high water velocities and a lack of wetted margin

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High water velocities – weirs and dams with narrow crests and large drops can create high water velocities and turbulence that act as a barrier to swimming fish species.

Lack of wetted margins – many of these structures lack the wetted margins that climbing fish species need in order to wriggle their way up and over in-stream obstacles.

Options

New weirs should be designed and constructed with fish passage as a major consideration, as this is likely to be essential in gaining resource consent. General principles for ensuring that fish passage is provided for can be found here:

Weirs (1.7 MB PDF)

Existing weirs and dams require retrofitting to allow fish passage, and there are a range of options to accomplish this.

  • Ramp fishways – these consist of boulder/cobble or artificial substrate ramps that cover either the whole width or a section of the barrier. They allow fish to swim over obstacles by reducing water velocities, creating resting areas and decreasing the slope.
    Ramp fishways (386.6 KB PDF)

  • Spat ropes – these ropes have been shown to be effective for climbing fish species to wriggle up and over obstacles. They can be cheaply installed on the downstream face of large weirs and dams where access for only climbing species is required.
    Spat ropes (223.8 KB PDF)

  • Nature-like channels – these channels replicate small sections of natural stream and are used as a bypass to allow fish to swim around moderate-sized dams and weirs.
    Nature-like channels (82.8 KB PDF)

Note: the pdf documents on this page are excerpts from ARC Technical Report 2009/084: “Fish Passage in the Auckland Region – a synthesis of current research".

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