Author(s): Youichi Yasuda; Yuuichi Aono

Linked Author(s): Youichi Yasuda

Keywords: Fish passage; Leading flow; Assembled boulders; Migration route; Local flow

Abstract: Generally, fishways should be installed on drop structures to enable upstream migration. Furthermore, the upstream flow downstream of the fishway is also important for assisting the upstream migration of swimming fishes. Regarding the upstream migration of multiple aquatic animals, Yasuda and Fuchino (2022) proposed the installation of continuously assembled large boulders. Inclined ramps using large boulders have been studied by various researchers [Pagliara et al. (2017), Kim et al. (2020), Chaudhary et al. (2021)], but stabilization methods combining large boulders have not been established. Results from field tests applying ramp structures using boulders confirm that continuously assembled boulders maintain stability even during flood periods [Yasuda (2025)]. Recently, a fish passage using 50cm-sized boulders was installed in the old boat passage of an irrigation weir (see Fig.11). Since the guide wall height of the boat passage is only about

DOI: https://doi.org/10.64697/iahr.proc.ise2026.abs.110

Year: 2026