Modeling radiocesium transport from a river catchment based on a physically-based distributed hydrological and sediment erosion model

Kinouchi, Tsuyoshi*; Yoshimura, Kazuya  ; Omata, Teppei*

We developed a distributed model to simulate the transport of water and contaminated sediment in a watershed hydrological system, and applied this model to a partially forested mountain catchment located in an area highly contaminated by the radioactive fallout derived from Fukushima Dai-ichi Nuclear Power Plant accident. Observed discharge, sediment concentration, and radiocesium concentration measured from June 2011 until December 2012 were used for calibration of model parameters. The simulated discharge and sediment concentration both agreed well with observed values, while the cesium concentration was underestimated in the initial period following the accident. Based on the simulation results, we quantified the long-term fate of radiocesium over the study area and estimated that the effective half-life of Cs deposited in the study area will be approximately 22 y due to the export of contaminated sediment by land-surface processes.