2025 Volume 81 Issue 16 Article ID: 24-16018
This study conducted rainfall-runoff and flood inundation analyses for the Kuma River basin during the July 2020 heavy rainfall event. Rainfall-runoff, flooding-inundation phenomena, and water balance of tributary watersheds were examined. The findings of this study were summarized as follows. (1) The water storage and balance in tributary basins varied depending on the basin characteristics, mainly land use. (2) Inflow from tributary basins, including the Kawabe River, was about the same as the Kuma River. (3) In the Hitoyoshi-Watari section, which was severely damaged due to inundation inflow from the tributary basins was 1,300 m3/s, corresponding to 16 % of the main river channel. (4) Due to the heavy rainfall pattern of this event, the approximate coincidence of the peak flow occurred between the main river and tributaries flowing into the Ichibu-Hitoyoshi water level monitoring section. (5) To mitigate the flood damage, reducing the flow rate at the Hitoyoshi City area by reducing the inflow from the basin or changing the peak flow occurrence between the main river and tributaries through flood control facilities is necessary.
