2020 Volume 76 Issue 1 Pages 177-188
Typhoon Hagibis that occurred in the beginning of October 2019 was one of a largest and powerful tropical cyclone and was considered to be the most devastating typhoon to hit Japan in recorded history. Extreme heavy rainfall caused massive impacts to Japan in general and to Marumori Town, Miyagi Prefecture in particular. In this study, a detailed field observation data obtained immediately after the flood in Marumori has clearly shown that many broken levee locations were caused by water overflow the river embankment at the constriction areas such as the tributaries junction and the intersection of the river embankment. A numerical simulation was performed to investigate the mechanism of embankment breaching in Marumori Town. According to the simulation results, the flooding water from the breached location in the upstream of Gofukuya River caused the broken levees in the downstream of Shinkawa River and Uchikawa River. In addition, the complete or partial damages of the levee are dependent on the duration of overflow and the maximum overflow water depth. The model results have also shown that the initial overflow locations in the downstream areas were occurred at the corner of a constricted areas and agreed well with the observed breaching locations of the levee in Marumori Town.
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