Author(s): Kimberley Kasischke; Mario Oertel

Linked Author(s): Mario Oertel

Keywords: fishway; block ramp; flow transition; stability; hydrodynamic forces; numerical investigation

Abstract: Fishways are important hydraulic structures that ensure the continuity of watercourses for aquatic organisms and the stability of river bed. Passage is often impeded by hydraulic cross structures or large bottom steps, which may require the construction of fishways. Block ramps are a nature-based solution to provide lower flow velocities, sufficient flow depths and resting areas for a variety of fish species and aquatic organisms. Three flow regimes for different discharge events have been identified in previous investigations: basin flow, wave flow and channel flow. There is still a major research deficit due to the transition between these flow regimes. In particular, the estimation of the forces that can lead to a failure of the structure due to the collapse of boulders should be analyzed in detail. For the analysis, a certain force determination is performed for an exemplary geometry of a crossbar block ramp. Forces are determined using numerical CFD simulations, carried out to identify flow transitions and calculate the hydrodynamic forces on different boulders for varying discharge events, and compared with experimental model data. Results show that simulated drag forces can be predicted with sufficient accuracy. However, it is clear that further geometries and discharge events need to be investigated, as the flow transitions could not be defined adequately. This preliminary study provides a numerical approach to verifying hydrodynamic forces acting on individual boulders for a crossbar block ramp design procedure.

DOI: https://doi.org/10.3929/ethz-b-000675921

Year: 2024