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Coordinating, Developing, and Delivering Highway Transportation Innovations

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Publication Number:  FHWA-HRT-14-064    Date:  August 2014
Publication Number: FHWA-HRT-14-064
Date: August 2014


Fish Passage in Large Culverts With Low Flow


The literature review for this study included identifying fish passage requirements, general approaches to designing culverts, and laboratory and numerical studies oriented to understanding and achieving fish passage. With respect to fish passage, stream simulation is generally considered the state of the art in fish passage design. Stream simulation attempts to mimic the conditions experienced by aquatic organisms upstream and downstream of the culvert within the culvert itself. The guiding principle is that if the organism can move up and down the stream, then it can also move through the culvert. Of critical importance is that by using this approach, the designer does not need specific knowledge of the habits and capabilities of specific species. This approach has allowed broader attention to aquatic organisms of many types rather than a singular focus on a fish species and life stage. The first comprehensive guide to stream simulation was developed by the United States Forest Service.(2) Subsequently, FHWA developed its variation on stream simulation.(1) Both documents provide references supporting the use of stream simulation. An earlier synthesis report prepared for FHWA provides a good overview of previous work in culvert design for fish passage.(3) The synthesis report, when used to identify culvert design specifications, facilitates consensus and expedites permitting for project delivery.

Laboratory studies have been conducted related to culverts and other hydraulic devices such as fishways. These studies used data collection techniques and approaches that are applicable to studying culverts. For example, Puertas et al. studied vertical-slot fishways using acoustic Doppler velocimeters to measure three-dimensional (3D) velocities to capture the flow structure and velocity distribution.(4) Magura details physical modeling to investigate the flow characteristics of circular corrugated structural plate (CSP) culverts with 10-percent embedment and projecting end inlets.(5)

Numerical methods have played an important role in estimating the velocity distribution at a stream cross-section or within a culvert. (See references 6 through 11.) Mathematical and computational methods can assist in the prediction of the velocity distribution when field data are unavailable or insufficient and laboratory data are limited. Blank et al. investigated the effect of culvert velocity on fish passage with CFD for estimating the 3D velocity field and characterized energy expenditure paths to identify passageways.(10) Haque et al. validated a 3D Reynolds-averaged Navier-Stokes (RANS) model to predict flow and stratification effects related to fish passage at hydropower dams.(12) House et al. presented a regression model that estimates the percentage of a cross-section suitable for fish passage in embedded culverts based on discharge, total cross-sectional area, Froude number, and relative roughness.(9)

Numerical models, validated by field or laboratory data, enable simulation of velocity patterns and secondary flow structures in complex natural channels and other hydraulic structures. (See references 13 through 16.) Khan et al. developed and validated a 3D CFD model of a dam forebay.(17)


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