2019 Volume 75 Issue 2 Pages I_1477-I_1482
Based on the observation data such as the rainfall and flood in the Takahashi River basin, and furthermore the field survey data on the inundation depth, sediment deposit and others in Mabi-cho flooded area caused by the West Japan torrential rainfall in July, 2018, the actual state and characteristics of the sediment deposit and the density of inundation water in Mabi-cho flooded area are examined. It is illustrated that (1) the thickness of the sediment deposit is less than 1% of the maximum inundation depth at each survey point, which has a tendency to be thinner than that due to tsunamis and (2) as leaving the broken point of river embankment, the thickness of the sediment deposit becomes gradually thinner. The cross-sectional average concentration of sediment in the inundation water and the density of the inundation water are estimated by introducing bold asummption on the three-dimensional shape of the flooded area and bold sediment deposit model, and then using the data on the sediment deposit obtained by the field survey. It is judged that the estimated density is smaller than that of the salt water.
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