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  • If a smooth bed culvert must be designed, then flow velocities for water depth up to 0.5 metres ideally should be no more than 0.3 m/s.

  • In sand and gravel-based streams, natural bed material should either be placed along the bed of the wet cells, or allowed to deposit in these cells. The hydraulic design of these culverts should allow for this added bed roughness which facilitates upstream fish movement.

  • In clay-based streams that do not experience significant movement of bed load sediment, artificial roughness units such as rounded stone, can be grouted across the bed of the wet cells to provide the desirable bed roughness and fish resting areas.9

  • If fish passage is desirable during bankfull flows, then consideration should be given to the placement of artificial sidewall roughness units along the cell wall immediately adjacent to the channel banks.

  • Where conditions allow, construct pools at both the inlet and outlet of the culvert to assist in the dissipation of flow energy and to act as resting areas for migrating fish.

© Catchments & Creeks Pty Ltd

  • If a low-flow channel is constructed within the base slab of the culvert, then ensure that the channel extends across the inlet and outlet aprons.

  • Debris deflector walls can be used to reduce the impact of debris blockages on fish passage while also reducing maintenance costs.

  • Maximise light penetration within the wet cells by maximising the height or diameter of the cells, and possibly by introducing skylights or grated stormwater inlets into the median strip of divided roads. These skylights are only required within the nominated wet cells.

  • To avoid the formation of a perched culvert and damage to the stream's bed and banks, erosion at the outlet should be controlled with the use of rock protection and/or the formation of a stabilised energy dissipation pool.

© Catchments & Creeks Pty Ltd

fish passage requirements for waterways crossings

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