Flood flow characteristics with sediment and driftwood in the mountainous stream

2020 Fiscal Year Final Research Report

• Project/Area Number: 18K13842
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 22040:Hydroengineering-related
• Research Institution: Public Works Research Institute
• Principal Investigator: Harada Daisuke 国立研究開発法人土木研究所, 土木研究所(水災害・リスクマネジメント国際センター), 研究員 (30795802)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Keywords: 中山間地河川 / 流路・河床変動 / 流木 / 微細土砂 / 平面二次元洪水流解析

Outline of Final Research Achievements

The present study developed methods to analyze the behavior of driftwood in terms of the convection-diffusion equation, and methods to evaluate the erosion rate of bed sediment composed of fine sediment by means of entrainment velocity. The proposed methods were tested by a series of flume experiments, and they were introduced in the depth-integrated 2-D flow model.　The methods were applied to analyze the three flood disasters that happened in mountainous rivers in Japan from 2017 to 2019. As a result, we proposed methods to analyze flood flow with a huge amount of sediment and driftwood, where the sediment and driftwood cause the bed deformation and that also affects the characteristics of flood flow.

Free Research Field

水工学、河川工学、流路・河床変動

Academic Significance and Societal Importance of the Research Achievements

2017年の九州北部豪雨における赤谷川，2018年の西日本豪雨災害における総頭川，2019年の東日本豪雨における五福谷川といった，中山間地河川において近年頻発する所謂「土砂・洪水氾濫」では，上流から多量の微細土砂や流木が供給された結果，下流域に甚大な被害をもたらしている．本研究の成果によって，これらの現象を数値シミュレーションで解析することが可能になり，今後の中山間地河川河道計画や避難計画，災害の復旧等に貢献するものである．