A Curved‐Bar Rack‐Bypass System With Innovative Foil Shaped Bars: Hydraulics, Operational Aspects, and Swimming Behavior of Downstream Moving Brown Trout

Abstract

Curved bar rack ‐ bypass systems (CBR‐BS) are a promising technology for diverting downstream moving fish away from hydropower intakes. A CBR functions as a mechanical behavioral barrier by creating high velocity and pressure gradients along its bars, guiding approaching fish that exhibit avoidance reactions towards the bypass. The original CBR design features a bar shape with spacings that narrow from the upstream to the downstream tip, which raises concerns about clogging due to foliage and floating debris. To address this issue, new foil‐shaped bars (f‐CBR) were developed with similar hydraulics while maintaining a constant bar spacing along the rack. To test its performance, a 1:1 physical model of a f‐CBR with a bar spacing of 25 mm was installed in an etho‐hydraulic flume. Live‐fish tests using brown trout were conducted at approach flow velocities of , 0.3, 0.6 m/s, with bypass‐to‐approach flow velocity ratios set at and 1.2. Additional tests with leaves and driftwood were performed to evaluate clogging probability of the f‐CBR. Flow fields were also numerically simulated for the tested flow conditions and linked to the fish behavior. Over all tested setups, fish guidance efficiencies between 47% and 66% were observed, while fish protection efficiencies ranged from 65% to 86%. These findings are compared with those from other types of behavioral fish guidance racks tested in both laboratory and field settings. Finally, potential measures for the optimal design of a f‐CBR‐BS are presented.