The 2017 July Northern Kyushu Torrential Rainfall Disaster—Geotechnical and Geological Perspectives

In July 2017, localized and torrential rainfall caused many landslides, debris flows, and flooding of rivers resulting in devastating damage to several areas of the Fukuoka and Oita prefectures of Kyushu, Japan. The authors conducted an extensive investigation of the damage covering several cities, towns, and villages of the Fukuoka and Oita Prefectures. The areas suffered from the disaster have many complicated geologies and geomorphologies, which exacerbated the damage. In this research, the authors focused on the landslides and debris flows that occurred in the Otoishi River basin. The characteristics of slope failures are analyzed, and the failures are classified focusing on the geological features. Finally, the slope failure mechanism is discussed.