Fundamentals of Culvert Design for Passage of Weak-Swimming Fish

Publication Date



baffles, culverts, design, design criteria, fish passage, hydraulic conditions, inlet, manual, swimming, swimming ability, water velocity, weir baffles

Report number


Publication place

Fairbanks, AK


Alaska Department of Transportation and Public Facilities


Properly designed culverts do not produce water velocities that exceed fish swimming abilities. Fish have two different musculature systems for swimming. A white muscle system generates power for short, vigorous swimming. A red muscle system furnishes power for long, sustained swimming. The culvert design must account for both swimming modes. Therefore, the engineer must know the hydraulic conditions where the fish swims. These conditions change throughout the culvert. The engineer determines acceptable hydraulic conditions for fish by matching known fish swimming power and energy capacities. Subcritical flow is necessary to pass weak-swimming, upstream-migrating fish. Therefore, this requirement precludes the use of inlet control. The engineer may use artificial roughness to create areas of slower water velocities within culverts. Examples of this are depressed inverts, weir baffles, and deep culvert corrugations. This manual presents design procedures to pass upstream-migrating, weak-swimming fish. The manual also display criteria for retrofitting existing culverts. This paper does not present cost-effective design criteria for strong-swimming fish.

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