Abstract
This report investigates the characteristics of heavy rainfall and flood inundation area due to heavy rain caused by Typhoon No. 19 in 2019. We obtained data on rainfall, inundated areas, and topographic characteristics of the affected area. We also examined the relationship among them. This study confirmed the following: (1) In prefecture-managed rivers, inundation occurred due to insufficient flow capacity within areas of heavy rainfall. Furthermore, reduced flow capacity was caused by rising water levels in the main river at the confluence. (2) In rivers under the jurisdiction of the Ministry of Land, Infrastructure, Transport and Tourism (MLIT), rainwater due to heavy rain upstream flowed into the river channel and downstream. It caused the water level in the river channel to rise in the downstream area where rainfall was relatively low. The rise of the water level caused inundation with levee failure. (3) Depending on the topographical characteristics, there were two types of floodplains: one that attempted to divert floodwater back into the river channel, and the other that acted as a retarding basin. (4) The area where the levee breach occurred in the Kanto region, where most of the land was used as a field and where the inundation flows were stored, may have served as a flood-retarding basin.
