Complex Sediment Particle Group Dynamics Analysis by s-137: Toward Prediction of Residence Time of Adsorbed Contaminants

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K12205
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 63010:Environmental dynamic analysis-related
• Research Institution: Tsuyama National College of Technology
• Principal Investigator: Taniguchi Keisuke 津山工業高等専門学校, 総合理工学科, 准教授 (80774794)
• Co-Investigator(Kenkyū-buntansha): 遠藤 徳孝 金沢大学, 地球社会基盤学系, 准教授 (60314358)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 河川 / 放射性セシウム / 水路実験 / 写真測量 / 混合粒径 / 砂礫洲

Outline of Final Research Achievements

When riverine sediment has a wide grain size distribution, the fine-grained fraction may be captured in the spaces between the large particles. We observed the process of capturing the fine-grained fraction through flume experiments, conducted photogrammetric surveys to determine topographic changes during flooding in a real river, and measured the grain size distribution and Cs-137 concentration of sediment samples. In the channel experiment, we observed cases where fine grains were retained under the coarse-grain fraction and mixed with the coarse-grain fraction in local eddies near large gravels. In a river, topographic changes before and after the flooding were measured by photogrammetry, and sediment samples were obtained. The changes in grain size distribution and Cs-137 concentration suggested that if the mixing ratio of each grain size fraction could be determined from the distribution, it would be possible to detect the replacement of fine particles using Cs-137 as a tracer.

Free Research Field

地形学

Academic Significance and Societal Importance of the Research Achievements

川の流れの中に土砂が堆積し、洲を作ることがある。普通は、大きな粒子ほど堆積しやすいが、大きな粒子と細かい粒子が混ざって運ばれている河川では、細かい粒子が取り込まれやすくなる場合がある。この研究では、セシウムの細かい粒子に吸着されやすい質を活かして、実河川の砂礫洲で細かい土砂の流失や再堆積の量を計算できないかと考えた。大雨の前後での調査の結果、新しくできた起伏の土砂と元からの土砂、両方の試料を比較することができた。原発事故由来のセシウム137を、その細かい粒子がもとからあったものか、新しく取り込まれたものかを判断する道具（環境トレーサー）として使うことができる可能性を示すことができた。