2021 Fiscal Year Final Research Report

Assessment of effective forest management to reduce driftwood disasters based on analyses of long-term water and sediment discharge using a distributed process-oriented model

Research Project

PDF

Project/Area Number	18H03957
Research Category	Grant-in-Aid for Scientific Research (A)
Allocation Type	Single-year Grants
Section	一般
Review Section	Medium-sized Section 40:Forestry and forest products science, applied aquatic science, and related fields
Research Institution	The University of Tokyo
Principal Investigator	Hotta Norifumi 東京大学, 大学院農学生命科学研究科(農学部), 准教授 (00323478)
Co-Investigator(Kenkyū-buntansha)	ゴメスクリストファー神戸大学, 海事科学研究科, 教授 (20800577) 廣嶋卓也東京大学, 大学院農学生命科学研究科(農学部), 准教授 (40302591) 甲斐田直子筑波大学, システム情報系, 准教授 (60456704) 鈴木拓郎国立研究開発法人森林研究・整備機構, 森林総合研究所, 主任研究員等 (60535524) 加藤顕千葉大学, 大学院園芸学研究院, 准教授 (70543437) 早川裕弌北海道大学, 地球環境科学研究院, 准教授 (70549443) 芳賀弘和鳥取大学, 農学部, 准教授 (90432161)
Project Period (FY)	2018-04-01 – 2022-03-31
Keywords	流木災害 / 土石流 / 土壌浸食モデル / 土砂災害対策 / 防災意識
Outline of Final Research Achievements	We examined the production, transport, and deposition of sediment and woody debris in forested watersheds, including sites where driftwood disasters had occurred, by field reconnaissance. We also used several models to describe the sediment dynamics. The results revealed significant variation of fluidity in landslide-triggered debris flows due to the liquefaction of fine sediments, and that accurate prediction of the post-landslide inundation area of sediment is critical for countermeasures against driftwood disasters. In addition, the topographical conditions of the headwater catchment affected the allocation of driftwood to debris flows and floods. Analyses of the long-term behavior of sediment and woody debris indicated that forest zoning to reduce driftwood disasters should consider the connectivity between the slope and channel system controlling the supply of sediment and woody debris into the watersheds.
Free Research Field	砂防工学，森林水文学
Academic Significance and Societal Importance of the Research Achievements	流木の生産と河道への供給が土砂と一体となって生じることに着目し，土壌浸食モデルをプラットフォームとすることで，異なる複数の土砂移動プロセスを流域内で総合的に評価することを可能にした．崩壊が河道まで到達せず流木化しない場合や，河道に到達しても安定化してそのまま腐朽し，長期的には土砂流出と一体化して緩やかに下流に到達する場合を含めて，流木災害のリスクを適切に評価するための枠組みを構築した．