Start Date

2018 4:20 PM

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

Abstract

The German Waterways and Shipping Administration (WSV) has to replace several weirs in the near future. In addition to maintenance and operation, the WSV is also responsible for the establishment of the ecological continuity, i.e. free migration of species like fish along the river and thus over weirs. The downstream migration over weirs with low to medium heads was a mostly neglected issue and was commonly considered to be an insignificant hazard for fishes. Recently, this assumption was tackled by fish biologists by applying design rules for plunge pools at fish bypasses to weirs. As a consequence, an additional plunge pool may be required in order to fulfill this criterion at a weir. In a numerical study with the three-dimensional computational fluid dynamics package OpenFOAM®, the hydraulic characteristics of a sharp crested weir were analyzed in detail, in particular the nappe deflection at the weir sill. The hydraulic conditions were evaluated in terms of accelerations and were compared to acceptable accelerations for different species in order to assess the possible endangerment of fishes. Additionally, the conditions for fish plunging into pools of acceptable depths were evaluated numerically with a numerical model based on the software StarCCM+. The results of both studies support the thesis that the “plunge pool criterion” is an insufficient tool to assess the safety of fish migration over weirs with significant overflow and that substantial further research is required in order to derive a suitable criterion that can ensure the safe passage of fishes over medium height weirs with low tailwater levels.

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May 17th, 4:20 PM

Numerical Study on the Hydraulic Conditions for Species Migrating Downstream over a Weir

The German Waterways and Shipping Administration (WSV) has to replace several weirs in the near future. In addition to maintenance and operation, the WSV is also responsible for the establishment of the ecological continuity, i.e. free migration of species like fish along the river and thus over weirs. The downstream migration over weirs with low to medium heads was a mostly neglected issue and was commonly considered to be an insignificant hazard for fishes. Recently, this assumption was tackled by fish biologists by applying design rules for plunge pools at fish bypasses to weirs. As a consequence, an additional plunge pool may be required in order to fulfill this criterion at a weir. In a numerical study with the three-dimensional computational fluid dynamics package OpenFOAM®, the hydraulic characteristics of a sharp crested weir were analyzed in detail, in particular the nappe deflection at the weir sill. The hydraulic conditions were evaluated in terms of accelerations and were compared to acceptable accelerations for different species in order to assess the possible endangerment of fishes. Additionally, the conditions for fish plunging into pools of acceptable depths were evaluated numerically with a numerical model based on the software StarCCM+. The results of both studies support the thesis that the “plunge pool criterion” is an insufficient tool to assess the safety of fish migration over weirs with significant overflow and that substantial further research is required in order to derive a suitable criterion that can ensure the safe passage of fishes over medium height weirs with low tailwater levels.