Author(s): Timothy W Haltigin; Pascal M Biron; Michel F Lapointe

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Keywords: Fish habitat; stream restoration; computational fluid dynamics (CFD); deflectors; separation zone; dynamic pressure

Abstract: Fish habitat rehabilitation projects often use paired stream deflectors to increase bed shear stress and maintain a deep pool. Many of these projects have been unsuccessful, mainly because of the lack of knowledge of the complex three-dimensional (3D) flow dynamics created by the deflectors. A 3D numerical model was used to simulate the flow field around stream deflectors in a laboratory flume. Predicted velocities were successfully evaluated against laboratory measurements. Deflectors ranging from contraction ratios of 0.1 -0.35 oriented to flow at angles of 30-150° were used for the simulations. Results show that the upstream dynamic pressure maximum, upstream flow separation distance, upstream downwelling extent, and total downwelling distance all increase with deflector angles. However, local minimum dynamic pressure, nose velocity amplification, downstream downwelling extent, and flow contraction width are maximized at angles closer to 90°. In general, maximum downwelling magnitudes increase for longer deflectors, with the greatest values being found for the 135° deflectors. Increasing the length of the deflectors tends to amplify most of the flow parameters. These findings have important implications for the design of paired deflectors in fish habitat rehabilitation projects where the objective is to maximize the pool size downstream of the obstructions.

DOI: https://doi.org/10.1080/00221686.2007.10525038

Year: 2007