Investigation of Flow Conditions that Hinder Upstream Passage of Small Migratory Fish for Pool-and-Weir Fishway Improvements

2023 Fiscal Year Final Research Report

• Project/Area Number: 22K20598
• Research Category: Grant-in-Aid for Research Activity Start-up
• Allocation Type: Multi-year Fund
• Review Section: 0604:Agricultural economics and rural sociology, agricultural engineering, and related fields
• Research Institution: Hirosaki University
• Principal Investigator: YATAYA Kenichi 弘前大学, 農学生命科学部, 助教 (70949487)
• Project Period (FY): 2022-08-31 – 2024-03-31
• Keywords: 魚道 / 通し回遊魚 / ニホンウナギ / ウキゴリ / プール間水位差 / 河川遡上

Outline of Final Research Achievements

A large model flume (length 5.5 m, width 1.4 m, height 1.4 m) was constructed to perform upstream migration experiments and flow velocity measurements under conditions of 15 cm and 20 cm upstream water level, targeting a full-scale stepped fishway weir section (weir thickness 30 cm, weir height 64 cm). In this experiment, the head difference among pools, which is the dominant factor controlling the maximum flow velocity in the overfall section, was systematically varied. As a result, the relationship between the trajectories and hydraulic characteristics of goby species (average body length 3.9 cm) during their upstream migration period and Japanese eels with an average body length of 15.3 cm, while ascending the overfall section, was investigated. Furthermore, the head difference among pools that makes upstream migration difficult was identified.

Free Research Field

農業水利学

Academic Significance and Societal Importance of the Research Achievements

日本の河川に設置されている魚道の60％以上が、階段式魚道である。これらの魚道の中には，ウキゴリ類等の小型通し回遊魚が遡上困難となっている事例が報告されている。また、ニホンウナギは近年、個体数が減少しており、その要因の一つとして、河川横断構造物による流程分布の分断が挙げられている。本研究成果は、こうした遡上阻害によって劣化した生態環境回復のための魚道の機能向上の知見となるものである。