STUDY ON OPTIMUM GEOMETRY OF STRIP ROUGHNESS IN OPEN-CHANNEL FLOWS FOR ANGUILLA JAPONICA MIGRATION

Abstract

 In recent years, Japanese eel population has been declining significantly, which is thought to be due in part to the discontinuity of the water level caused by dams and weirs. In order to remedy this situation, fishways are installed in river crossing structures. Fishway is also expected to support the upstream reaction force and improve fish migration rate by installing pier roughness. In this study, the wooden cleats installed on the bottom of an open channel were varied into four types of roughness shapes, and the total length times velocity was varied from 1-4 (1/s) to investigate the suitable cleat shape for migration of Japanese eels. The results showed that, under the experimental conditions, Japanese eels could easily adhere their trunks to cleats with a square cross section of 10 mm in height and 10 mm in width in downstream direction and with 20 mm wide and 5 mm deep recesses at 20 mm intervals in crosswise direction. Japanese eels were found to adhere to cleat roughness easily and to use it as a resting place and an object to support upstream reaction force.