Study on decadal-scale sediment storage and transport in mountain catchment

2021 Fiscal Year Final Research Report

• Project/Area Number: 19K23681
• Research Category: Grant-in-Aid for Research Activity Start-up
• Allocation Type: Multi-year Fund
• Review Section: 0603:Forestry and forest products science, applied aquatic science, and related fields
• Research Institution: Hokkaido University
• Principal Investigator: Koi Takashi 北海道大学, 広域複合災害研究センター, 准教授 (40845294)
• Project Period (FY): 2019-08-30 – 2022-03-31
• Keywords: 流域貯留土砂 / 山地森林流域 / 航空写真 / SfM / 土砂移動 / UAV / 降雨出水 / 1973年北海道小谷石災害

Outline of Final Research Achievements

Altough a large amount of unstable sediment is supplied to the catchment when large-scale landslide event occurs, the movement of post-production of such supplied sediment is not clearly understood due to few research cases. This study clarified the movement of stored sediment in the catchment where there was a large-scale landslide event in the past. The study site is the Nakanosawa catchment of Kotani'ishi in Shiriuchi town, Hokkaido, where multiple landslides and debris flows occurred due to heavy rainfall in 1973. As a result of time-series aerial photograph interpretaions and field surveys, after the 1973 event, moderate-scale sediment movements continued from the upper reaches to the middle reaches of the catchment, and minimal sediment tranportations occurred in the lower reaches for a long period of time until recent years. On the other hand, it was revealed that sediment discharge to reach the catchment outlet occurred during the 2013 rainfall event.

Free Research Field

砂防学

Academic Significance and Societal Importance of the Research Achievements

気候変動の影響により豪雨頻度が増加し，今後もこの傾向が継続することが懸念されている。わが国はその地形・地質的特徴から過去に大規模な土砂生産があった流域が多く存在するにもかかわらず，こうした生産土砂がその後どのような挙動を示すのかといった知見はほとんどなかった。本研究は，流域内に存在する貯留土砂が降雨出水に応じてどのような挙動を示すかの想定に寄与することが期待でき，防災対策を検討する上で重要な知見を提示できた。本研究で対象とした流域のように，土砂生産から数十年経過後に大規模な土砂流出が引き起こされていたことは災害直後の施設整備やその後のモニタリングの重要性を改めて示している。