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  • excessive flow velocities within the culvert.

  • inadequate flow depth within the culvert.

  • excessive water turbulence.

  • debris blockage of the culvert.

  • excessive culvert length and a lack of aquatic habitat and "rest" areas within the culvert.

  • inadequate lighting within the culvert.

  • excessive variation in water level across the culvert outlet (waterfall effect).

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WETLAND FLOW CONTROL STRUCTURES

Flow transfer between rivers and adjacent wetlands is often controlled with the use of floodgates or wetland inlet structures.

These structures are generally similar in design to road culverts and can cause fish passage problems. The operation of wetland inlet structures has been investigated by the Australian Landscape Trust on the Lower Murray River.

Research findings and operational recommendations for wetland flow control structures are available through the Australian Landscape Trust. For more information refer to their website at www.australianlandscapetrust.org.

CAUSEWAYS

Causeways are usually low cost, near-level waterway crossings, constructed slightly above the natural bed level of the watercourse and designed in a manner that promotes the formation of thin sheet flow passing over the road surface. In some cases a low-flow pipe may be placed under the causeway to keep the crossing dry during periods of low flow.

The most common fish passage problems associated with causeways include:

  • excessive flow velocities through the low flow pipe.

  • debris blockage of the pipe.

  • inadequate lighting within the pipe.

  • excessive fall in the water level across the causeway or at the outlet of the low

  • flow pipe (waterfall effect).

  • inadequate flow depth over the causeway during minor stream flows.

  • sediment runoff from the approach roads.

FORDS

Fords differ from causeways in that the road crossing is formed directly on the channel bed resulting in the formation of a "wet" crossing. Flow depths across a ford are likely to be similar to natural stream conditions, unless the crossing is above the natural bed level creating a waterfall effect on the downstream edge. Vehicles travelling across a ford can disturb sediments causing water quality problems which are known to affect fish health and habitat values.

fish passage requirements for waterways crossings

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