Masahiro KAIBORI, Atsuhiko KINOSHITA, Teruyoshi TAKAHARA, Yasuyuki TADA, Eiji NAGANO, Shigeaki BABA, Yoshinori ARAKI, Shigemitsu SUGIHARA, Toru SHIMADA, Daiichirou HORI and Kazuya KOIZUMI
Abstract
On July 28, 2013, the districts of eastern part of Yamaguchi Pref. and of western part of Shimane Pref. have been seriously damaged by a heavy rain]storm in only one day. Especially, a lot of slope failures and debris flows occurred intensely around Susa Town, Ato Town, and Tsuwano Town in both Prefectures. The areal rate of slope failures of these districts exceeded 1.0% in a dense area. The probabilities of the rainfall as a cause of the disaster were less than 1/1,000 years and were extremely rare cases. However, according to the field investigation, most of slope failures have been recognized as shallow failures and following sediment movements were not deep. Moreover, a lot of small holes, through which ground]water sprang out, and traces of surface]flows have been found out not only on the slope]failure sites, but also on the forest slopes. These phenomena can be regarded as typical features of an extreme torrential rainfall.
Key wordsFslope failure, debris flow, extreme torrential rainfall, field investigation