Hydraulic Optimization of Symmetric Wart-Type Baffle Spacing for Fish Passage in Open-Channel Flows

Abstract This study investigates the role of symmetric wart-type baffles in facilitating fish passage under supercritical flow conditions in an open-channel flume. Experiments were conducted in a 7 m long, 0.5 m wide flume with a 2% bed slope at the Ujigawa Hydraulic Laboratory, Kyoto University. The impact of two baffle spacings (20 cm and 30 cm) on hydraulic characteristics was assessed and compared to a smooth channel. Velocity profiles, flow depth, and turbulence intensity were measured across ten longitudinal points to evaluate flow heterogeneity and energy dissipation. Results indicate that baffles significantly reduce flow velocity and create low-velocity resting zones critical for fish migration. The 20 cm spacing configuration proved most effective, offering a balance of reduced velocities (0.5–0.9 m/s) and sufficient hydraulic diversity to support energy-efficient fish passage. In contrast, the 30 cm spacing resulted in higher velocities and reduced low-velocity zones, potentially challenging weaker swimmers. Turbulence intensity was lowest with 30 cm spacing ( TI mean = 0.053), indicating smoother flow but fewer refuges compared to 20 cm spacing ( TI mean = 0.069). The smooth channel exhibited uniform, high velocities, unfavorable for most fish species. These findings highlight the importance of optimized baffle spacing in fishway design to enhance river connectivity and support aquatic biodiversity.