Numerical simulation of rock ramp fishway for small-bodied Great Plains fishes

Abstract

The preservation and restoration of fish populations and their habitats have become significant aspects of environmental conservation efforts. Effectiveness of fish passage structures plays a crucial role in facilitating the successful migration of various fish species. This research focused on utilizing Computational Fluid Dynamics (CFD) models to assess the hydraulic conditions within a rock ramp fishway with varying slopes and flow rates for small-bodied Great Plains fishes. This work built upon a previous study conducted by Swarr (2018) to investigate the passage success rates of three small-bodied fish of the Great Plains of North America: Flathead Chub (Platygobio gracilis), Arkansas Darter (Etheostoma cragini), and Stonecat (Noturus flavus) within a full-scale laboratory rock ramp fishway. Using commercial software, Flow-3D Hydro, CFD models were developed to simulate and predict hydraulic parameters such as flow depths, velocities, and turbulence kinetic energies (TKEs) within the fishway. To validate the accuracy of the CFD models, predicted flow depths and velocities were compared with observed data for two slopes: 2% and 10%. The CFD model results indicated that increasing slopes and flow rates led to corresponding increases in the mean values of the studied parameters. The mean depth varied from 0.051 m on the 2% slope to 0.068 m on the 10% slope. The mean velocity increased from 0.272 m/s on the mildest slope to 1.003 m/s on the steepest slope. Additionally, the average TKE ranged from 0.003 J/kg on the 2% slope to 0.014 J/kg on the 10% slope. The study highlighted that higher velocity and TKE values at steeper slopes may have contributed to the poor upstream passage rate, particularly for weaker swimmer species, like the Arkansas Darter, at slopes greater than 4%, as observed in the physical model study. Findings demonstrated that the presence of rocks in the fishway created diverse flow conditions. Low-velocity zones observed behind rocks within the fishway may provide favorable conditions for successful fish ascent. This research showcases the capabilities of CFD in providing quantitative data for optimizing fish passage structure design and contributing to conservation efforts.