This paper reports simulations of soil erosion, sediment movement, and the resulting migration of cesium-137 (137Cs) in eastern Fukushima Prefecture after the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in Japan. We quantified these processes with a simple, novel, and fast simulation model developed previously with the Universal Soil Loss Equation (USLE) and a Geographical Information System, using coarse region-scale data as input. We focused on the land-use factor in the USLE because land use has a potential large effect on soil erosion, thereby offering insight into effective environmental countermeasures. Results indicate that, while a large portion of the study area is forest, only a small fraction of the total soil loss and 137Cs movement is transported out of the forest boundary. Analysis of 14 river basins showed that approximately 1013 Bq of 137Cs is exported to the ocean annually in early after the accident. This value corresponds with estimates of direct leakage from the FDNPP of 1.7 × 1013 Bq between June 2011 and September 2012, and of 2.4 × 1013 Bq from a leakage on 21 August 2013. Detailed estimates for the Ukedo River Basin, most contaminated after the FDNPP accident, further indicated that 104 t of sediment and 1012 Bq of 137Cs migrated into the Ogaki Dam reservoir, which provides a buffering effect downstream. Field-based estimates are within the same order of magnitude as model predictions. This study suggests the important roles of land use and dam reservoirs on the movement of soil, sediment, and cesium
these factors should be considered for developing remediation options for Fukushima and other lands contaminated with radiocesium.