Resilient Structures, Stream Connectivity, and Aquatic Organism Passage Through Culverts

The Minnesota Department of Transportation has released a new report that includes recommendations for maintaining aquatic organism passage and stream connectivity at roadway crossings. In addition to meeting traditional hydraulic and roadway capacity goals, culverts may be designed to facilitate the movement and life cycle needs of fish and other aquatic organisms at road-stream intersections.  Along the way, resiliency of the structure is improved by maintaining more natural stream velocity and water elevation.

Clear-span of bankfull channel width maintains more natural velocity

The report includes and excellent summary of best practices for aquatic organism passage and stream connectivity as follows (Table 2.4.1):

1. Design the culvert slope to match stream channel slope

2. Place the culvert to best match stream alignment

3. Design the culvert opening to bankfull channel width or slightly greater

4. Provide culvert flow depth comparable to channel flow depth for aquatic organism passage (not over-wide and too shallow)

5. Provide a continuous sediment bed with roughness similar to the channel

6. Maintain continuity of sediment transport and debris passage, similar to adjoining reaches

7. Design for safety to the general public, longevity, and resilience

These common-sense recommendations may be used by designers in any location to not only improve fish passage, but also reduce debris and sediment buildup which can lead to increased scour potential. The full report is available from the Minnesota Department of Transportation.

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