Integrated watershed modeling for simulation of radio-cesium migration after flood events in the catchment near the Fukushima Dai-ichi Nuclear Power Plant

Sakuma, Kazuyuki   ; Kurikami, Hiroshi  ; Malins, A.  ; Yamada, Susumu  ; Funaki, Hironori ; Niizato, Tadafumi  ; Machida, Masahiko  ; Kitamura, Akihiro   

The environments of Fukushima near the Fukushima Dai-ichi Nuclear Power Plant have been contaminated by the explosion accident of the plant caused by the Great East Japan Earthquake on 11 March 2011. The contamination level and air-dose rate behavior at present and in future are significant concern for the people used to live nearby. Most dominant radioactive material is Cs at present and its migration is considered to be driven by soil erosion and subsequent transport. To estimate the amount of soil sedimentation and the Cs migration, a three-dimensional hydrological model of the catchment was developed focused on the Ogi-no-sawa catchment, located 15 km southwest of the Fukushima Dai-ichi Nuclear Power Plant. Base on the developed hydrological model, top soil transport and resulting radio-cesium movement was simulated. For the modeling and simulation, physics based code the General-purpose terrestrial fluid-flow simulator GETFLOWS model, which is one of the tools for watershed modeling, was applied. The simulation results were compared with monitored data of the amount of water discharge and concentration of suspended solids for model testing. As a result of the study, the soil and Cs redistribution patterns at various scales of flood events could be predicted based on the results of modeling and simulation.