Experimental and field approach to the hydraulics of nature-like pool-type fish migration facilities

Nature-like fish migration facilities have gradually become a common type to ensure longitudinal connectivity of fish movements in running waters. This article presents verification on hydraulic and geometric parameters of nature-like pool-type fish passes via experimental and field investigations. The experiment verified that the maximum streamwise velocity near a slot ranged from 0.8-1.0 time of the theoretical maximum velocity. Large vertical recirculations presented below sills, moved downstream with the increase in discharge, and were likely to vanish or to change the rotation direction with high flow conditions. High turbulent kinetic energy distributed immediately downstream from boulder sills instead of along the water jet. Fieldwork was conducted at a full-width ramp in Kolbermoor and a partial-width ramp in Leitner in Bavaria under low, mean and high flow conditions to investigate the flow and geometry characteristics in real constructions and under various hydrologic conditions. The results for velocity show confidence in the method to obtain the maximum value around a slot by measuring at one depth only. Instead of flow velocity, water depth played a more critical role in the performance of a nature-like fishway, in particular under low flow conditions, and so did the arrangement of boulders along a sill. A detailed hydraulic/geometric investigation, together with biological monitoring, should be conducted to identify appropriate criteria on assessment of fish free passage at nature-like fish migration facilities