令和元年度台風19号による洪水災害と降雨流出特性

Abstract

Typhoon No.19 caused severe flood disasters in October 2019 with total 142 levee breaching. Our field survey conducted mainly in Tochigi and Miyagi prefectures suggested that flooding along the tributaries were categorized into: A) ponding-type at river merging points with back-water effects, B) flowing-type on floodplains in flat areas, C) flowing-type from valley bottom plains or alluvial fans, and D) water and sediment disasters in mountain areas. Many flooding locations in Tochigi prefecture, including the upstream of the Watarase River, were categorized into C) with some cases of B). On the other hand, in the upstream of the Abukuma river, the group C) dominated with a few exceptions of D). These differences were mainly due to the rainfall intensity, contributing areas and topography. Numerical simulation covering the wide range indicated that flood peak runoff height reached or exceeded 30 mm/h along such tributaries where the levee breaching occurred in Tochigi prefecture.