Abstract
Transport of suspended sediment (SS) and radiocaesium was investigated for every particle size in the Okawa River system. Turbid water was sampled during flood at five stations, and particle-size distribution was measured. SS was collected using three classes of filter: pore size 0.3 μm, 20 μm, and 40 μm, and the concentrations of SS, 137Cs, and 134Cs were analyzed. The weight of SS caught by each class of filter and the weight of the same classes calculated by the size distribution did not coincide. Gaussian distribution was applied to the clogged particles below the pore size for the filtered sample. Total Cs concentration had a negative correlation with the calculated center diameter (d50); total Cs was approximately 2,000 (Bq/kg) when d50 was 5 μm and it decreased to 1,500 (Bq/kg) when d50 was 50 μm. Furthermore, total Cs was highest at the start of the storm discharge and it decreased toward the peak of flood. It was found that the transport of Cs was affected by both the size of the suspended particles and the phase of the flood discharge.
