¹³⁷Cs discharge during heavy rainfall events from the five coastal rivers were simulated by GETFLOWS. Fig. 1 and 2 show the amount of ¹³⁷Cs discharge and the ratio of discharge (discharge amount/inventory), respectively.

• The discharge amount of ¹³⁷Cs from the Ukedo river is the highest among the five rivers. It is due to the largest catchment area and the largest inventory of ¹³⁷Cs (Fig.1).
• However, the ratio of ¹³⁷Cs discharge amount to the inventory of the Ukedo river catchment is the lowest (Fig.2). It is due to the existence of a dam in the middle reach that prevents sediment and radiocesium to flow downstream.
• In contrast, the ratio of ¹³⁷Cs discharge from the Maeda river shows the highest. It doesn’t have a dam. The fact that the highly contaminated area is paddy field with high erodibility also results in the high discharge ratio (Fig.2).

Fig.1　Five river basins near the Fukushima Daiichi Nuclear Power Station (Odaka River, Ukedo River, Maedagawa River, Kuma River, Tomioka River) and the upper reaches of the Ota River, Inventory of ¹³⁷Cs deposits in the Oginozawa basin in the Tomioka River basin
(4th Aircraft Monitoring Data, November 2011)

• 

  Fig.2　Amount of ¹³⁷Cs discharge

• 

  Fig.3　Ratio of ¹³⁷Cs discharge to inventory

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• Will radioactive contamination continue to accumulate in reservoirs due to the inflow of radioactive cesium from rivers? 【Effect of the upstream dam on ¹³⁷Cs accumulation in the riservoir beds】
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Reference

1. Sakuma, K., Kitamura, A., Malins, A. Kurikami, H., Machida, M., Mori, K. Tada, K., Kobayashi, T., Tawara, Y. and Tosaka, H. (2017): Characteristics of radio-cesium transport and discharge between different basins near to the Fukushima Dai-ichi Nuclear Power Plant after heavy rainfall events, Journal of Environmental Radioactivity, vol. 169-170, 137-150. https://doi.org/10.1016/j.jenvrad.2016.12.006