Abstract
The accident at the Fukushima Dai-ichi Nuclear Power Plant in March 2011 resulted in the widespread deposition of radiocesium in and around Fukushima prefecture. Riversides have an additional contamination risk through deposition of material containing radiocesium transported from upstream. In our previous research (Nishikiori and Suzuki, 2017) we developed a decontamination method in a river bank in 2014; however, the decontaminated site had a recontamination risk. In this study, we evaluated the effectiveness of plant removal as a countermeasure against recontamination because plants favor the deposition of highly-contaminated fine particles. Although suspended solids with high radiocesium concentrations were transported, under plant-removal conditions (2015–2016), sediment deposited in the flood channel was sandy with low radiocesium concentrations. In 2017, one year after the plant recovery, somewhat muddy sediment with high radiocesium concentrations was deposited during medium rainfall events; the plant biomass would explain the amount of fine sediment that was deposited. Additionally, large typhoons introduced sandy sediment even on the densely vegetated flood channel. Thereby, the air dose rates did not increase during the observation period. Plant removal may control the deposition of highly contaminated sediments and be an effective countermeasure for recontamination in the flood channel.
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