[HCG34-P02] Radiocesium Inter-Annual Variations and Spatial Dynamics in Watershed in Iitate, Fukushima, Japan
Keywords:Radiocesium, Soil erosion, Annual Variations, Spatial Dynamics
In this study, fixed point observations was conducted on two rivers, Hiso river and Mano river, in Iitate village, Fukushima Prefecture from 2013 to 2018. In addition, multiple observation points were set up in watersheds, and simultaneous water sampling was done at multiple points. We measured SS concentration and 137Cs concentration from water samples, grasped the long-term change in 137Cs runoff, and identified the catchment area where 137Cs runoff was noticeable.
The 137Cs concentration of SS dropped drastically with extreme large flood due to Typhoon Etau in 2015, and the concentration remained low until 2018. The same result was obtained in 2018. In Hiso river, 137Cs concentration of SS in 2018 increased slightly compared to 2017. This is thought to be the effect of the decontamination work in the Nagadoro district.
As a result of simultaneous multipoint observation, spatial distribution of 137Cs concentration in the watershed was changing as merging the branch streams into the main stream. In addition, it was revealed that sediment with high 137Cs concentration flowed in from Nagadoro district where decontamination works was incomplete.