Study on levee breach and mitigation caused by the remerging flood flow in a rapid meandering river

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K04268
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 22040:Hydroengineering-related
• Research Institution: Utsunomiya University
• Principal Investigator: IIMURA KOSUKE 宇都宮大学, 地域デザイン科学部, 准教授 (30642128)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 令和元年東日本台風 / 那珂川水系荒川 / 中小蛇行河川 / 氾濫 / 氾濫戻り流れ

Outline of Final Research Achievements

Typhoon Hagibis in 2019 caused levee breach at 27 locations in 13 small and medium-sized rivers in Tochigi Prefecture. In meandering rivers, the remerging flood flow may have contributed to the collapse of the opposite bank. Experiments and numerical analyses were conducted to clarify these effects. The narrower the opening width at the point where the remerging flood flow occurs, the greater the flow velocity of the remerging flood flow. It was confirmed that this flow causes an area of high flow velocity to spread to the opposite bank. It was also confirmed that the narrower the meandering river channel, the greater the flow rate through the floodplain, and a wide area of high flow velocity was formed on the opposite bank of the opening.

Free Research Field

河川工学

Academic Significance and Societal Importance of the Research Achievements

中小蛇行河川において生じた氾濫流の戻り流れによる連鎖的な決壊現象に関して，下流側開口部の幅が戻り流れの対岸流況へと与える影響を明らかにし，下流側開口部から早い流速で蛇行河道へと戻る流れが生じ，対岸にも流速の速い領域が広がるように流れることを示した．那珂川水系荒川の決壊例を見ると，本研究結果のように対岸に高速域が生じ，侵食決壊へと至った可能性が大いに考えられ，中小蛇行河川における戻り流れの危険性を示した．