Flow Characteristics of a Full-cross-sectional Overflow Stepped-pool Type Fishway and Fish Swimming Behavior:—Case study on full-cross-sectional overflow stepped-pool type fishway in the Iwaki River Diversion Weir—

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In order to study the relationship between fish swimming behavior and flow characteristics, we conducted field observations and monitored the behavior of fish using an underwater TV camera over a period of two years(2006,2007) in the full-cross-sectional overflow stepped-pool type fishway in the Iwaki River diversion weir, where field ascending fishes and fishway hydraulic surveys are being conducted. The results showed the following: 1) the area most used by ascending fish was that in the center of the pool and at the lower rear part of the upstream wall notch, while the area least used was that around the downstream wall; 2) most of the fish swam near the bottom of the pool (0 to 20 cm from the bottom) and ascended the fishway while swimming freely in the low-flow velocity areas at the center of the pool, sensing the high-velocity flow around the notches and orifices in the pool; and 3) swimming fish ascending through the area at the rear of the wall notch swam in the area along the wall, where an upward flow is generated, and underneath the overflow nappe, while bottom-oriented fish with suckers ascended the fishway by adhering to, and moving along, walls and side-walls..
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