Keywords:Decontamination works, soil erosion, Cs-137, river
The Fukushima Daiichi Nuclear Power Plant (FDNPP) on March 2011 accident released massive amounts of radiocesium into the terrestrial environment such as Cs-137 and Cs-134. The Niida river basin (265 km2) on the north eastern part of Fukushima prefecture is indeed a case in point. The river basin has a highly contaminated area on its upstream part and evacuation have been ordered, and the cropland and paddy field becomes grassland in the summer of 2011, but the downstream part has not contaminated so much. The upstream area of the basin had been subject to decontamination works, such as scraping surface soil and reversal tillage and so on, since 2012.