| Most conventional studies of fishways deal with the relationship between the shape of a fishway and the climbing ratio of fish against the current passing through the fishway and the relationship between the shape of a fishway and the flow pattern. There are no sufficient studies on what swimming behaviors fish take toward a particular flow pattern formed inside the fishway that have been conducted to-date. Because fish migrate to upstream inside a fishway while maintaining a delicate and complicated flow pattern、 it is considered difficult to design an appropriate fishway shape of fishway without sufficiently understanding the relationship between the flow pattern and swimming behavior of fish inside the fishway. Under such circumstances、 we conducted experiments of Pool-and-Weir fishways which have been used widely in Japan with respect to the following three points (1)、 (2)、 and (3) aiming at contributing to the enhancement of the methods for designing and evaluating Pool-and-Weir fishways. 1): To achieve the relationship between the flow pattern and the swimming behavior of Japanese daces (Approximately 10cm) inside the pool from the change in the scale of the Pool-and-Weir fishway pool (e.g.: pool depth and pool length). 2): To achieve the flow pattern inside the pool from the change in the shape of the top of the weir of a Pool-and-weir fishway. 3): To achieve the climbing motions of Japanese daces for the representative flow pattern obtained from issue 2) above. A summary of the experimental results is enumerated below. 1) The climbing frequency and route are largely different based on pool water depth and pool length. 2) The climbing of a Japanese dace starts when it enters the downstream current. 3) There are three cases when a Japanese dace enters the downstream vein. The first case where a Japanese dace swims from the bottom current of route 1 to the downstream current and then enters the downstream vein. The third case is where a Japanese fish swims from the middle layer of route 2 to the downstream current and then enters the downstream vein、 and the case where a Japanese dace floats upstream pointing its head downstream、 and it accidentally enters the downstream vein. 4) A Japanese dace swims in a fixed space with a flow velocity less than 60cm/s、 and then leaves for an above mentioned climbing route. 5) A Japanese dace hardly uses the space with an unstable vector among the relatively slow flow spaces、 which are formed in the pool as a fixed space. 6) A Japanese dace cannot deal with the sudden change of flow direction even in a rapid flow place where the Japanese dace can swim、 and cannot start climbing there. 7) The ease of fish climbing depends importantly on the relationship between the flow pattern to be determined by the pool water depth、 the pool length、 the overflow quantity、 and the gap of adjacent weirs. 8) In even one pool consisting simply of two weirs、 the swimming behavior of a Japanese dace reacts in a complicated manner to the flow pattern. 9) Depending on a slight difference in the weir shape or overflow depth、 an utterly different streaming flow、 plunging flow、 and slanting flow are formed in the pool、 and the ease of fish climbing is largely different. 10) Since a streaming flow greatly changes the flow direction、 the posture of a Japanese dace is easily disturbed there. 11) Since in a plunging flow a Japanese dace moves frequently downstream in a pool、 its climbing frequency decreases. 12) Since in a slanting flow many individuals are caught in the counter flow area、 the climbing frequency of a Japanese dace decreases. As results、 for improve the climbing ratio of fish、 I thought that the vertical vein should be resolved. Therefore、 I suggested fishway weirs with slope with relative roughness. A summary of effect of the fishway with slope is enumerated below. 1) To flow down into the pool in the vein obtuse、 a fish can be easily entered the vein and can migrate to upstream. 2) With the establishment of regular roughness、 the closer to the roughness、 veins are flowing down the slope on the absorbing. 3) Crustacean claws hooked a crude degree、 can upstream to the upstream. |
