Elucidation of drainage basin characteristics by focusing on the longitudinal and planar morphology of river channel from the headwaters to the mouth

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K18397
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 4:Geography, cultural anthropology, folklore, and related fields
• Research Institution: Tohoku University
• Principal Investigator: Hori Kazuaki 東北大学, 理学研究科, 教授 (70373074)
• Co-Investigator(Kenkyū-buntansha): 田中 靖 駒澤大学, 文学部, 教授 (80348888)
• Project Period (FY): 2021-07-09 – 2024-03-31
• Keywords: 流域 / 河道 / 河相 / DEM / 連結性

Outline of Final Research Achievements

The study examined the relationship between the characteristics of a river system and its longitudinal profile from its source to its mouth in Japan, specifically for "Class A" rivers. A more detailed longitudinal profile of the river was created by overlaying the river's centerline with the 10m DEM. In their downstream portions, many rivers showed sudden changes in gradient, known as transition points, with elevations concentrated around 10m or 5m. The study also found that the representative grain size of the riverbed sediments decreased sharply near the transition point. This could be attributed to backwater effects associated with the Holocene transgression. The research also investigated the impact of anthropogenic structures such as bridges and dams on the longitudinal connectivity of rivers. The total number of these structures was approximately 13,000, or 1.12 per km.

Free Research Field

地理学

Academic Significance and Societal Importance of the Research Achievements

河川や流域を扱う様々な学問分野において、河相・河川景観や水、土砂などの連結性への関心が高まっているなか、一級河川本流の源流から河口までを対象とした、詳細な河床縦断形を作成できた。また、下流部における縦断勾配や河床堆積物の粒径の急減は、古くから知られ、現在も議論が続いているgravel-sand transition（GST）と関連しており、本課題においては、海進にともなうバックウォータ効果がこの現象に反映されている可能性を指摘した。河相・河川景観や水，土砂などの連結性（コネクティビティ）を検討する上での基礎的データ（とくに人為的影響に関する指標）を提示することができた。