Study on chage of hydrological processes and environments in small rivers under the population decline

2023 Fiscal Year Final Research Report

• Project/Area Number: 20H00256
• Research Category: Grant-in-Aid for Scientific Research (A)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Medium-sized Section 22:Civil engineering and related fields
• Research Institution: Tohoku University
• Principal Investigator: Kazama So 東北大学, 工学研究科, 教授 (50272018)
• Co-Investigator(Kenkyū-buntansha): 原田 守啓 岐阜大学, 流域圏科学研究センター, 准教授 (00647042) ; 堀 智晴 京都大学, 防災研究所, 教授 (20190225) ; 糠澤 桂 宮崎大学, 工学部, 准教授 (20725642) ; 渡辺 一也 秋田大学, 理工学研究科, 准教授 (50463097) ; 小森 大輔 東北大学, 工学研究科, 准教授 (50622627) ; 横尾 善之 福島大学, 共生システム理工学類, 教授 (90398503) ; 峠 嘉哉 東北大学, 工学研究科, 助教 (90761536)
• Project Period (FY): 2020-04-01 – 2024-03-31
• Keywords: 過疎 / 河川計画 / 河川環境 / 中間山地 / 底生昆虫 / 川じまい

Outline of Final Research Achievements

Changes in population national data over time show that in all prefectures of the Tohoku region, the river areas and river lengths with zero population are not expanding at a constant rate, but are accelerating. The acceleration is approximately 0.7 to 4.5 km2/year2 (river length 9 km/year2). It is inferred that the nutritional status of rivers has decreased due to the decline in population, and that there has been a decrease in sessile and swimming types, as well as a decrease in sessile and swimming types. It is thought that the annual maximum flow rate of small and medium-sized rivers in the Tohoku region increased by 1.5 to 6.7% due to the decrease in rice fields in areas with a declining population. When the river channel and land use were changed taking inundation, the annual maximum discharge decreased by about 7%, approximately 1% less than no inundating conditions.

Free Research Field

水文学

Academic Significance and Societal Importance of the Research Achievements

地域のコミュニティに強い影響を与える中小河川の管理に注目しており，これらの基礎となるデータを提供し，河川管理を放棄する地域の特定や，自然河川へ導く方法を見出したことは，人口減域の河川管理に一石と投じたといえる．川じまいを多面的に考察した本研究は，水文学，河川工学だけでなく，水を中心に考えた流域圏の都市計画学，環境工学，生態学，農村工学，社会学などの関連分野に大きなインパクトを与え，その学術的かる社会的意義は大きいと考える．