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Design For Fish Passage at Roadway - Stream Crossings: Synthesis Report

11 Future Research Needs

How to use this chapter

  • Learn what the remaining knowledge gaps are in the design of culverts for fish passage

11.1 Sediment Movement and Stability

Coarse sediments commonly collect and deposit upstream from culverts that have experienced a flood sufficiently large to be constricted at the entrance and raise the water-surface elevation. The following issues are unknown for this case:

  • Impact of deposits on scour at the culvert entrance and headwater elevations during floods
  • Ability of the stream to mobilize the sediment deposit and transport it through the culvert

Methods for predicting the stability or movement of sediment through culvert barrels are based on greatly simplified assumptions, such as unconstricted, open channel flow and clear water conditions. The impacts of constricted (accelerated) flow, pressure flow and sediment-laden conditions are not well understood and need basic research to better describe the hydraulics of flow for Hydraulic Simulation.

11.2 Flow Hydraulics

The variation of velocity and turbulence in culvert barrels is not well understood, even for such a simple condition as a non-embedded corrugated metal culvert. Recent work by Richmond et al. (2007) begins to describe the flow complexities in such a culvert. More work is required.

Even less work has been done on velocity and turbulence characteristics in baffled culverts (Morrison 2006). Each proposed baffle configuration would benefit from standardized hydraulic testing to establish locations of both reduced and increased velocity and turbulence zones for a range of discharges.

11.3 Life Cycle Costs

There are insufficient data available that describe the total life cycle costs of culverts. For example, there are only qualitative statements in this report that state wider-span culvert expenses may be offset by lower maintenance and stream-channel protection costs following construction. Work is required to populate a database with standardized costs for culvert operations on a life cycle basis. This will require State DOTs to cooperate in following consistent procedures for describing all costs, including both design and maintenance of the culvert and the local stream reach.

11.4 Fish Movement and Response

To allow specific engineering of fish passage structure, further studies of fish response to turbulence, darkness, velocity, and varying water depths and substrates are necessary.

11.5 Monitoring

Monitoring of current installations is an important step in understanding the impact of state-of-practice design techniques on stream structure, function, maintenance and biology. Development of case histories will allow others to learn from the successes and failures of current fish passage installations. Such studies can contribute to techniques for adaptive management.

11.5.1 Hydraulic Simulation Structures

As fish swimming capabilities and movement requirements are better understood, it will be possible to better engineer these structures. However, variations in dynamic stream systems and in local hydrology, sediment and debris loads will ensure that a conservative approach is required.

The Hydraulic Simulation procedures described in this report can be better documented with additional research on sediment transport and flow hydraulics (see sections 11.1 and 11.2).

11.5.2 Hydraulic Design Structures

Gregory (2004) recommends the incorporation of before and after studies at Hydraulic Design-based structures. This could include field and test bed experimentation with live fish, or comparison of fish passage within the natural reach to passage through retrofitted culverts (Gregory et al. 2004). Studies should compare performance results with assumptions inherent in passage criteria.

Research is also necessary in the emerging practice of slip lining culverts in retrofit situations. Such practice can reduce or eliminate fish passage at structures formerly capable of passing fish. Work is needed in methods to provide for fish passage for these cases.

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Updated: 04/07/2011


Bert Bergendahl

United States Department of Transportation - Federal Highway Administration