Flood Flows in the Mabi Town District, Kurashiki City, Due to the 2018 West Japan Severe Flood Disaster

Abstract

Severe flooding occurred in the district of Mabi Town, Kurashiki city, located on the lower reaches of the Oda River, in the 2018 West Japan heavy rain disaster. Several dikes on the Oda River and its tributaries such as the Suemasa and Takama Rivers broke during the disaster. Severe breaks occurred on both sides of the dikes at the 700 m point of the Suemasa River. Flood streams from both the left and right banks damaged buildings near the dike break points and formed oppori due to the strong flood flow. Floodwaters streaming from the breaking points flowed through vacant or agricultural land, avoiding buildings. Downstream, the Suemasa River has raised bed conditions between the points around 700 m and 400 m. The horizontal river channel around the section is not straight but bends in an S-shape. In addition to the backwater from the Oda River, these characteristics of the Suemasa River might have influenced the dike breaks and severe flooding. On the other hand, in the area where a dike break occurred at the confluence of the Oda and Takama Rivers, the floodwaters flowed north, which differs from the normal direction. There were also other flood flows from the east. This western direction of flood flow might have increased the inundation damage.