Evaluation of the Migration Environment of Ayu under the Different Flow Conditions

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Other Title
  • 異なる河川流況下でのアユの遡上状況と遡上環境の評価
  • 異なる河川流況下でのアユの遡上状況と遡上環境の評価 : 八東川(千代川水系)永野堰の事例
  • コトナル カセン リュウキョウ カ デ ノ アユ ノ ソジョウ ジョウキョウ ト ソジョウ カンキョウ ノ ヒョウカ : ハチ ヒガシガワ(チヨ カワミズケイ)ナガノ セキ ノ ジレイ
  • — A case of the Eino weir in the Hatto River, Sendai River system —
  • ― 八東川（千代川水系）永野堰の事例 ―

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Not only the environment inside a fishway, but also that of the route to the fishway is considered as one of the important factors for river creatures to succeed in upstream migration. This study aims to evaluate the upstream migration of Ayu and the flow characteristics at the downstream of an ogee crest weir including fishway under the different river flow conditions. We clarified the flow velocity and direction at the downstream of the weir near the fishway entrance for Ayu. We also focused on the number of Ayu migrating through the fishway and the number of the fish trying to migrate over the weir directly, and the fluctuation of flow on the weir during the migration season of Ayu. Considering the flow velocity and direction, the flow preferred by Ayu appeared at around 20 m to 40 m away from the left bank fishway when the water depth on top of the weir crest was 9.7cm. Results of hydrological measurement and analysis showed that the flow depth fluctuation, which was observed when a lot of Ayu tried to migrate over the weir, occurred intermittently after the month of June in the past three years. Generally, it has been reported that the main migration season is in May in the research area, but this study showed the possibility of predicting the suitable days for observing the migration after the main migration season.

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