Abstract
New types of fish guidance structures with vertical curved bars and a subsequent bypass system represent a promising technical solution for the protection and guidance of downstream moving fish at run-of-river hydropower plants and water intakes. These so-called “curved-bar rack bypass systems” (CBR-BSs) function as a mechanical behavioral barrier and are characterized by low hydraulic losses, a symmetrical downstream flow field and an overall high fish guidance efficiency in the laboratory for a wide array of European freshwater fish species. This paper presents the results of the hydraulic and live-fish laboratory tests of an optimized CBR-BS configuration with a bar spacing of 50 mm and 30° rack angle to the flow direction. The tests were conducted with six different fish species in an ethohydraulic laboratory flume at different approach flows (0.5 m/s, 0.7 m/s) and different bypass entrance velocities (0.6–1.0 m/s). A numerical model was used to simulate the flow fields in the CBR-BS in order to link the fish behavior to the hydrodynamic cues created by the CBR-BS. Lower approach flow velocities decreased the hydraulic cues of the CBR, which led to more rack passages. A 20% velocity increase towards the bypass entrance significantly increased the fish guidance efficiency compared to a 40% velocity increase. The tested CBR-BS resulted in overall higher interspecies fish protection and guidance efficiencies compared to the more commonly applied horizontal-bar rack with a narrow bar spacing of 20 mm. Recommendations for a sustainable and cost-effective application of CBR-BSs are given.
Highlights
Functioning as physical barriers, and those with wider bar spacings functioning as mechanical to the approach flow direction and can be divided into Fish guidance structures (FGSs) with narrow bar spacings functioning as behavioral barriers
The normal behavior of the different fish species in the laboratory flume of the present study suggests that the light intensity did not stress the fish
For European eel, the fish guidance efficiency (FGE)* and the fish protection efficiency (FPE)* are both substantially higher for the horizontal-bar racks (HBRs) compared to the CBR. These results indicate that the CBR could overall lead to higher average fish protection and guidance, minimizing operational issues compared to the HBR
Summary
Water 2020, 12, 3244 downstream moving fish from hydropower and water intakes, guide them and transport them downstream without harm. Downstream moving fish from hydropower and water intakes, guide them and transport them. 10°–45° to the approach flow direction and can be divided into FGSs with narrow bar spacings. Functioning as physical barriers, and those with wider bar spacings functioning as mechanical to the approach flow direction and can be divided into FGSs with narrow bar spacings functioning as behavioral barriers. The former keep fish from turbine entrainment with clear bar spacings sb = 10–30 physical barriers, and those with wider bar spacings functioning as mechanical behavioral barriers
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