A Three‐Dimensional Computational Fluid Dynamics (CFD) Model Analysis of Free Surface Hydrodynamics and Fish Passage Energetics in a Vertical‐Slot Fishway

A three‐dimensional (3‐D), computational fluid dynamics model of a vertical‐slot fishway was used to characterize fishway hydrodynamics. The computational grid of a seven‐pool fishway, consisting of about half a million hexahedral and prism cells, simulates the spatial variations of water surface and velocity in the model domain. Model results indicate a strong 3‐D velocity field in the fishway, with eddies, flow separations, vortices, upwellings, and downwellings. Velocities and drag forces encountered by upstream migrating fish and energy expenditures in ascending the fishway are determined from the fishway hydrodynamics. The computed results are consistent with published information. Based on burst swimming speeds, the species of salmon Oncorhynchus spp. capable of migrating through the fishway were identified. Because the upriver spawning migration of adult salmon is energetically expensive, a quantification of energy expenditure in the fishways could be utilized for optimizing the design, operation, and management of fishways. Though this paper presents a model of a vertical‐slot fishway, the modeling approach is applicable to other types of fishways.