[M-AG34] Radioisotope migration: New development for radioisotope migration study related to 1F NPP accident

[MAG34-P02] Temporal patterns of riverine ¹³⁷Cs concentrations during high-flow events

*Yoshifumi Wakiyama¹, Hyoe Takata¹, Keisuke Taniguchi², Takuya Niida³, Yasunori Igarashi¹, Alexei Konoplev¹ (1.Institute of Environmental Radioacitivity, Fukushima Universiy, 2.National Institute of Technology, Tsuyama College, 3.KANSO TECHNOS CO., LTD)

Keywords:Cs-137, Catchment characteristics, Kd, Typhoon

Understanding riverine ¹³⁷Cs dynamics during high-flow events is crucial for improving predictability of ¹³⁷Cs transportation and relevant hydrological responses. Different temporal patterns of ¹³⁷Cs concentrations in river water are found in existing literature on ¹³⁷Cs dynamics during high-flow events. Although such differences may reflect catchment characteristics, there is no comprehensive analyses for the relationships. This study explores catchment factors controlling temporal pattern on riverine ¹³⁷Cs concentrations based on datasets obtained for high-flow events. Datasets obtained at 13 points in 6 river water systems were subject to the analyses. No significant catchment factor explaining mean values of normalized concentrations of ¹³⁷Cs and apparent Kd was found. When approximating ¹³⁷Cs concentrations and Kd value as a power function of suspended solid concentration (Y=α X ^β), the power of β in the equations for dissolved ¹³⁷Cs concentration and Kd showed negative and positive correlations with the logarithm of the watershed area, respectively, and the positive and negative values of β reversed when the catchment area was on the order of 1000 km² or larger. This indicates that the concentration of dissolved ¹³⁷Cs tends to decrease in larger catchments in peak discharge phase and vice versa for smaller catchments. These results suggest that the temporal pattern of dissolved ¹³⁷Cs concentrations depends on watershed scale.