Impact of Extreme Typhoon Events on the Fluvial Discharge of Particulate Radiocesium in Fukushima Prefecture

Abstract

Nakanishi, T.; Ohyama, T.; Hagiwara, H., and Sakuma, K., 2021. Impact of extreme typhoon events on the fluvial discharge of particulate radiocesium in Fukushima prefecture. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 310–314. Coconut Creek (Florida), ISSN 0749-0208. Two huge typhoons that occurred in October 2019, Hagibis and Bualoi, caused considerable flood damage in Fukushima Prefecture. There is concern about the radiocesium discharge to the coastal area related to such flood events from the river systems near the Fukushima nuclear power plant. In this study, we quantitatively evaluated the sediment and 137Cs discharges from the Ukedo River catchment based on the field observations conducted over 6 years. In 2019, approximately 90% of the annual sediment and 137Cs discharges occurred during the typhoon events (Hagibis and Bualoi). This sediment discharge was almost twice that related to the largest ever flood event since the Fukushima nuclear accident, which was caused by the typhoon Etau in September 2015. However, the 137Cs discharge related to the Hagibis and Bualoi events was two-thirds of the Etau event; the particulate 137Cs concentration in river water decreased during the observation period, showing an effective half-life of 2.2–3.9 years. Moreover, the 137Cs discharge during the two typhoon events in 2019 accounted for only 0.1% of the 137Cs deposition in the catchment, and the impact of radiocesium on the coastal area was extremely limited.