Base Information Q&A SiteJAEA

Radioactivity Dynamics in River System

(2014)

Does the concentration of radioactive cesium increase due to the resuspension of sediments by heavy rains?

Investigations at the Ogaki dam in Fukushima Prefecture have revealed that the flow rate downstream of the dam is low even during periods of high reservoir water levels. Therefore, it appears that it is difficult for reservoir bed sediments to be resuspended. The turbidity at the surface of the lake is due to sediment inflow from upstream.

Vertical distribution of flow rate from upstream to downstream (downstream of silt fence) of Ogaki dam lake at high water-level time

Fig.1 Vertical distribution of flow rate from upstream to downstream (downstream of silt fence) of Ogaki dam lake at high water-level time

Map is cited from Map data by Geographical Survey Institute

Fig.2 Map is cited from Map data by Geographical Survey Institute

Fig.3 Vertical distribution of turbidity and temperature of water from upstream to downstream of Ogaki dam lake during a high water level period

In the upstream region, flow rates at the reservoir bottom were around 10 cm/s at high water-level time. In this period, turbid water moved to middle and lower layers. In the downstream (downstream of fence), on the other hand, apparent change of flow rate was not observed even at the time of water discharge.