Study on the Hydraulic Characteristics of a Combined Fish Collection Channel and Fish Guide Weir System for a Fish Lift

To address the difficulty of attracting and aggregating fish at the entrance to a fish lift collection channel under conditions of low downstream discharge and low river velocities below a dam, this study optimized a combined fish guide weir and fish collection channel configuration using three-dimensional numerical simulation and physical model tests. The results showed that the fish guide weir produced weir-crest velocities above the adopted hydraulic velocity-barrier design criterion of 1.2 m/s and formed a flow field oriented toward the channel entrance. However, it also increased velocities in the collection channel to more than 1.2 m/s, exceeding the hydraulic design range derived from the swimming capacities of the target fish. A combined optimization strategy consisting of lowering the crest elevation of the fish guide weir, installing one large and two small flow-regulating piers in a triangular arrangement, and locally lowering the channel bed reduced velocities along the key migration pathway in the collection channel to 0.3–0.6 m/s. This created a low-velocity corridor with hydraulic conditions potentially suitable for the upstream passage of small-bodied target fish. This study provides an effective technical solution and design basis for improving hydraulic conditions for fish attraction under conditions of low downstream discharge and low river velocities below the dam.