Critical Rainfall Thresholds for Hydrological Processes Leading to Debris Flow due to Torrent Bed Material Scouring

Yasushi SANO, Takashi YAMADA, Tsuyoshi IKESHIMA and Sadakazu MATSUMOTO

In this study, we employ the 10-minute rainfall intensity and the effective rainfall with a half-life period most similar to the characteristics of torrent bed material water storage in the storage type model to calculate and evaluate the critical rainfall thresholds for hydrological processes leading to the generation of debris flow due to torrent bed material scouring. Critical rainfall thresholds for hydrological processes leading to debris flow since 2008 were effective rainfall of 41.2 mm and 10-minute rainfall of 6 mm for pipe flow without generating a debris flow, effective rainfall of 129.1 mm and 10-minute rainfall of 8 mm for a clogged pipe exit without generating debris flow, and effective rainfall of 126.8 mm and 10-minute rainfall of 19 mm for debris flow generation. These results suggest that a pipe flow has a small possibility of debris flow generation. For a clogged pipe exit, the amount of water stored in the torrent bed material meets the quantitative conditions required to generate a debris flow, indicating that a 10-minute rainfall of 19 mm or more may increase the possibility of a debris flow occurrence.

2018/1 104-109