Hydraulic impacts of one-sided wart-type baffles under supercritical flow: Experimental Insights toward optimized fish passage in diversion tunnels

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Hydraulic structures like dams, weirs, and culverts disrupt river connectivity, threatening aquatic biodiversity by impeding fish migration. This study evaluates the hydraulic performance of one-sided wart-type baffles in a diversion tunnel under supercritical flow, focusing on their impact on velocity, turbulence intensity (TI), and low-velocity refuges for fish passage. Experiments were conducted in a 7.0 m tilting flume at Kyoto University, with a 2% bed slope and 0.20 m baffle spacing. Baffles reduced velocities by 10–20% compared to smooth channels, creating heterogeneous flow fields and resting zones critical for fish. Mean TI increased from 7.59% (smooth) to 10.34% (baffled), indicating enhanced turbulence and energy dissipation. The Hydraulic Passage Index showed higher velocity deficits (9.57% vs. 7.94%), reflecting reduced flow efficiency but improved ecological functionality. These findings highlight baffles’ effectiveness in facilitating fish passage, offering insights for optimizing fishway designs.