Radioactivity Dynamics in River System
ＱHow do rainfalls affect turbidity and radioactive cesium concentrations in river water? 【Example of analysis】
ＡThrough analysis, we estimated responses (turbidity and radioactive cesium concentration in river water) to various rainfall patterns at the headworks.
When the concentration of suspended solids is high in river water (i.e., water is turbid), cesium concentrations tend to be high in that river water.
After a heavy rain, the cesium concentration in river water can remain high for a few hours to a few days.
Using the Ukedo basin as the sample, we estimated the river’s response to various rainfall patterns at its outlet works and headworks (turbidity and radioactive cesium concentration in water) by a calculation model called GETFLOWS (Fig. 1).
Calculation results indicate that the higher the suspended solids concentration is, the higher the cesium concentration is, as shown in Figure 2.
This suggests the possibility that water intake decisions at the headworks can be made from the suspended solids concentration (turbidity), which is easy to measure.
However, the plots of the suspended solids concentration and the cesium concentration also show that there is a wide variation depending on the rainfall pattern and the location of the headworks.
Figure 3 shows some chronological changes in the concentrations of suspended solids and cesium after rains at outlet works and headworks.
It indicates that although rainfalls result in an increase in the concentration of both suspended solids and cesium, the trend of increase varies by cesium distribution in the river basin and by the presence or absence of a dam. River water may remain turbid for a few hours to a few days.
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