Author(s): Keiko Muraoka; Ryuji Yasuda; Daisuke Tahara; Keigo Nakamura
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Keywords: No Keywords
Abstract: Fish passage design and fish guidance systems are important for the migration of fish. These facilities need to account for multiple species of fish because their swimming ability varies with body length, body shape, and fin morphology. But, in Japan, these factors are not always accounted for while constructing fish passages. Most fish passage designs that lack natural fish passages have been developed for strong swimmers such as salmonid species in western countries. These modern design methods for fish passages have been used in Japan for half of the century. They often arranged for Ayu fish (Plecoglossus altivelis) juveniles based on their burst swimming speeds. In the case of Naruka Ozeki weir in Kuzuryu river, fish passages have been established for Ayu fish, Sakuramasu trout (Oncorhynchus masou), and Japanese fluvial sculpin (Cottus pollux), which migrate during the same season. However, the flow discharge and drops in the fish ladder were designed for suitable flow for Ayu fish migration. For the guidance of Sakuramasu trout, which come up through deep areas, highvelocity flow toward the center of the river was created as fish guide for the fish passage. Observation of the stream regime around the fish passage and Sakuramasu trout suggested that possible improvements can be achieved without the need for any reconstruction, both for Ayu fish and Sakuramasu trout. The high flow velocity seemed to present a barrier to the entrance Sakuramasu trout to the fish passage, so the flow discharge of the fish guide and sluice gate next to it was decreased to refuge guidance flow toward the center of the river. In addition, the flow discharge on the fish ladder was increased to create high-velocity flow directly connected to the fish passage. Field examinations for several years showed that both Ayu fish and Sakuramas trout could pass the weir. Additionally, our experimental study shows that the flow discharge increasing change flow characteristics in the fish ladder, especially at the top of the weir, the straight flow line and submerged flow creates a thin migratable area for Ayu fish and Japanese fluvial sculpin along the top of the weir, and these weak swimmers could pass the weir if they could find the main flow on the fish ladder. In the case of Naruka Ozeki, it was assumed that the shallow depth of the pool and the rounded weir top created sufficient flow for both species.
Year: 2018