Roughened channel fish passage design addresses problematic streambed materials
When asked to alleviate flooding issues by designing drainage improvements in an area with clay soils, Mead & Hunt delivered a unique solution. The solution recognized the importance of aquatic habitat and the movement of aquatic species, even down to the sediment beneath the water.
Fish passage design issues
Manmade barriers to fish movement and migration are a significant factor in the decline of fish populations. Examples of barriers are culvert crossings at roads, railroads and trails.
Stream Simulation: An Ecological Approach to Providing Passage for Aquatic Organisms at Road-Stream Crossings shares that fish movement is more than needing to search out food and mates. Fish survival depends on “habitat quality and continuity for aquatic communities.” This means fish passage design has moved beyond simple grade and hydraulic adjustments for fish locomotion. Today, modern approaches employ a holistic look at the entire stream corridor.
One element of the stream corridor is the bed material in the stream. The bed material varies by region, stream, and reach within a stream. The bed material can have both direct and indirect effects on fish mobility and on food and spawning habitat. It influences hydraulic processes and geomorphologic phenomena related to:
- Stream energy dissipation
- Grade control
- Riffle and pool creation and stability
- Temporal aggradation and degradation of material (as the streambed is washed away or replenished by various flow events)
Hydraulic design process: Bed materials
The best method of selecting bed materials for restoring stream corridors in new or retrofitted culverts is to match what is native and natural. This involves an accounting of the existing bed gradation, often including a systemic pebble count of various sizes.
When the project is a retrofit or adjacent to a streambed disturbed by development or other activities, the stream corridor review is performed at the nearest undisturbed reach. The chosen reach is designated a reference reach.
Reconstruction of a natural, stable streambed with matching characteristics is not possible if the reference reach exhibits a bedrock bottom or is predominately made of clay materials. In this case, I would recommend using the roughened channel design concept, described in Water Crossing Design Guidelines. This design uses “a graded mix of sediment to create enough roughness and hydraulic diversity to achieve fish passage.”
Roughened channel concept: Roslyn, Washington
Mead & Hunt is using the roughened channel option for our client, the City of Roslyn. Roslyn is nestled in a mountain dell on the eastside of the Cascade Range in the state of Washington. Roslyn is pushing forward with various drainage improvements to alleviate flooding issues.
The South A Street project includes replacing perched, dual corrugated metal pipe culverts where a tributary of Crystal Creek crosses a residential street. The local, unconsolidated clay soils provided multiple design challenges. Our solutions included:
- Potential for settling issues was reduced by using a full-bottomed box structure instead of an open-bottomed arch culvert.
- Streambed restoration in and near the culvert was designed using a custom mixture of Washington State Department of Transportation-specified streambed materials.
The project will deliver aquatic habitat continuity, as well as provide safe and reliable drainage connection for the community.
ABOUT THE AUTHOR
Having started experimental work in stream hydraulics and coastal erosion at the age of 10, Bob Thayne now tackles his client’s stormwater and flood control needs with high-tech computational modeling. “I love to figure out what the water is going to do,” says Bob. “I use that information to provide water resources solutions.” And he still likes to play with water.
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