| Summary: | 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.
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