Hydraulic design aspects of rock-weir fishways with notch for habitat connectivity

Abstract Nature-like fishways have been installed at many migration barriers in recent years to mitigate the effects of human development and habitat fragmentation on fish. The design of these fishways determines the flow characteristics and ultimately the success of these passage facilities. This study numerically investigates the hydraulic properties associated with small passage openings (notch) that are provided in rock-weir-type fishways. Two distinct flow regimes, weir and transitional, were identified. The rock-weir with notch ensured suitable hydraulics for fish migration and sufficient fish resting areas in weir pools. A dimensionless weir coefficient was introduced to existing depth–discharge relationships to compute the weir flow more accurately. A reduction factor for the maximum velocity was also proposed as a function of discharge. This study optimized the design of rock-weir fishways considering passage notches based on fish resting zones, volumetric dissipated power, and performance for upstream fish migration.