Author(s): Dikshya Khadka; Sunit Palikhe; Umesh Singh; Pawan Kumar Bhattarai; Meg Bahadur Bishwakarma
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Keywords: Pool-and-orifice fish passage hydraulic performance turbulence characteristics
Abstract: The rivers of Nepal, which drain the Himalayan landscape, are home to at least 200 indigenous freshwater fish species, including some of the rarest in the world. Hydropower plants, a key driver of the country’s economic growth, disrupt the longitudinal connectivity of the aquatic ecosystems, necessitating effective fish passage structures to ensure fish migration and biodiversity conservation. The fish passages implemented in Nepal are primarily based on design guidelines developed on widely studied fish species, such as salmon, found in North American and European Rivers. Additionally, the fish passages in the Run-of-River hydropower projects need to operate across a wide range of flows, depending on availability of river flow, which can result in varying hydraulic conditions at different flows. However, these structures are not monitored, so their hydraulic performance remains poorly understood. This study investigates the hydraulic performance of one of the earliest implemented fish passages in Nepal at the Jhimruk Hydropower Project (HPP). The fish passage of this project is of a pool-and-orifice type, consisting of a short-inclined cylindrical orifice, inspired by Bonnyman's 1958 design but with notable design changes. A scaled model of the fish passage, with an undistorted scale of 1:5, was constructed at Hydro Lab to conduct hydraulic experiments and assess the hydraulic characteristics within the passage under full supply conditions. Velocity, Turbulence Kinetic Energy (TKE), and Reynolds shear stress (RSS), were analyzed. The velocity field results revealed that while the fish passage can accommodate strong swimmers, it may pose significant challenges for slow swimmers and juveniles. Additionally, the resting areas for the recovery of fish were insufficient due to the high turbulence in the pool, indicating hydraulic barriers that could hinder the passage of even strong swimmers.
Year: 2025