Effects of Forest Managements on Fluvial Disasters in terms of Sediment Yields and Transports

2019 Fiscal Year Final Research Report

• Project/Area Number: 17K06578
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Hydraulic engineering
• Research Institution: The University of Tokushima
• Principal Investigator: MUTO Yasunori 徳島大学, 大学院社会産業理工学研究部(理工学域), 教授 (40263157)
• Co-Investigator(Kenkyū-buntansha): 田村 隆雄 徳島大学, 大学院社会産業理工学研究部(理工学域), 准教授 (40280466)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: 総合土砂管理 / 森林 / 土砂生産 / 流砂 / 河道災害 / 流砂量計測法

Outline of Final Research Achievements

We conducted field measurements on precipitation, water levels in the streams and undergrounds, and sediment discharge in 2 watersheds whose catchment areas are a few km2. From the results we can draw a relation between cumulative rainfall in one event and corresponding sediment runoff with exponential functions. The coefficients and power indices of the functions depend on forest characteristics in addition to topography and geological features of the watershed. When considering the sediment runoff per square meter, the watershed mainly covered by natural forests, and/or having denuded lands within it, show a larger value at its fiducial stage, but its increment in accordance with rainfall increase is less, compared with that of coniferous forests. Applying these concepts together with the derived functions, we estimated the annual accumulated sediment runoff from the whole river basin, 247 km2, and obtained a reasonable result.

Free Research Field

工学

Academic Significance and Societal Importance of the Research Achievements

本研究では，従来から指摘されてきた地形や地質などの土砂生産・流出に関与するパラメータに加えて，崩壊地の有無や林齢などの森林の人的管理の影響がかなり寄与している可能性を示した点に新規性がある。ここで得られた成果は，流域管理において森林管理が，洪水流出量の調節のみならず土砂動態の制御の面からも重要であることを指摘した点で，研究の今日的意義は大きい。簡便な方法によって流域全体からの流下土砂量をある程度の精度で予測できたことは，適用限界が示されなかった点は課題として残るものの，実用に結びつく発展性が認められる．