Study on flow characteristics in vertical slot fishways regarding slot layout optimization

Design of effective fishways is becoming increasingly important. This paper focuses on the effect of the angle of deflection (α) between small and large baffles in a vertical slot fishway (VSF). A reliable depth-averaged two-dimensional numerical model PCFLOW2D was used to perform simulations of various VSF configurations, including six angles of deflection, two slot sizes, two large baffle sizes and four water level differences between adjacent pools. The results showed the important influence of α on depth-discharge curves and maximum velocities at the slot which both strongly affect the fishway efficiency. With larger α, up to 42% smaller discharges and up to 33% smaller maximum velocities were calculated. In cases with small α and larger slot sizes much greater maximum velocities than theoretically calculated using over simplified formula were modeled (up to 62%). The important effect of transverse displacement of the slot on discharge and maximum velocity was evaluated. As expected, the most important parameter that determines the discharge and maximum velocity in the fishway is water level difference between adjacent pools. With slot layout optimization it is possible to achieve the same discharge and maximum velocity even at larger water level differences between adjacent pools which obviously reduce fishway construction costs.