Author(s): M. Ura; K. Onitsuka; J. Akiyama; H. Yamaguchi
Linked Author(s): Kouki Onitsuka, J. Akiyama
Keywords: Pool-and-weir fishway; Velocity measurements; Burst speed; Migration
Abstract: A pool-and-weir fishway consists of weirs and pools. A fishway of this type has been installed beside of a large weir in the Onga River, Japan. The difference of the water level between the headwater and the first pool (0.37m) is greater than 0.15m, so that the falling velocity from the headwater to the first pool is higher than the burst speed of small fishes, and hence they could not migrate from the first pool to the headwater. It was found from field observation and measurements that the following conditions are necessary for fish migration in the case of a pool-and-weir fishway; i) falling velocity flows over the weir must be lower than burst speed of fish, ii) difference of the water level between adjacent pools is expected to be less than 0.15m, iii) flow in the pool must belong to a plunging flow, iv) instantaneous velocity component in the streamwise direction around the fish must take the downstream value and those in the vertical direction must take downward value when fish jump out of the water. In this fishway, the level of the headwater is required to keep constant for irrigation. Therefore, it is impossible to satisfy condition ii). In this study, considering conditions i), iii) and iv), an improvement to allow fish to migrate for the fishway is proposed on the basis of the experiments in the model flume.
Year: 2003