Successful steep gradient fish passage culvert designs provide fish migration paths and resting areas using key features that create diversity in flow velocity, depth, and energy dissipation patterns.

Key feature types are:

• Randomly placed stone
• Constructed channel features
• Fishways

Culverts that use the first two key feature types are countersunk and backfilled with a graded stone and sediment mix. As culvert slopes increase, effective fish passage and stable streambed becomes more difficult to achieve due to increases in flow velocity and turbulence. Stabilizing the streambed often requires sediment retention sills (SRS) or more abundant use of larger sized bed material or both. SRS are often used for controlling flow submergence at installations on small steep streams. Culvert span-to-stream width ratio, burial depth, length, and slope vary for each key feature type.

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	Randomly placed stone uses cobble and boulder-sized stone distributed throughout the bed material mix and on the bed surface that creates enough roughness to produce flow depths and velocities comparable to the natural stream channel. Bed forms tend to evolve and devolve with changing flow conditions.
Randomly placed stone
	Constructed channel features are channel features observed in the stream, including banks, stone sills, boulder clusters, and log sills, that are recreated or simulated within the culvert. The features are usually constructed of cobble and boulder-sized stone, and designed to be stable under a wide range of flow conditions.
Constructed channel feature
	Fishways are culverts equipped with specific structures designed for optimizing fish-passage. Structure types include weirs for creating pools and baffles for creating roughness. Baffles are typically lower than weirs and may be slotted. The culverts are not backfilled with streambed material.
Fishway culvert