Author(s): Hayato Kotani; Tatsuhiko Uchida; Shinnosuke Sasatani; Takuya Inoue; Misako Hatono; Akihito Kaji; Junji Komori; Hideki Miyata; Masahiro Kaibori

Linked Author(s): Tatsuhiko Uchida

Keywords: Debris flow; Bedrock groundwater; Surface layer groundwater; Effective rainfall

Abstract: The aim of this study was to investigate the temporal-spatial variation characteristics of groundwater levels in mountainous slopes in response to rainfall, in order to understand the mechanism of landslides, debris flows, and associated the sediment-flood disasters, and reduce their damages. The temporal variations in groundwater levels at several points in both bedrock and surface layers were measured, and the correlation between effective rainfall and groundwater level variations was examined. The results showed a strong positive correlation between the half-life of effective rainfall and the lag time of groundwater level variation to rainfall hyetograph. We found that these time scales of the ground water variations are related to the depth. Although the groundwater level variations in the bedrock were found to have long time scales of the lag time and effective rainfall, they exhibited different responses with short time scales of effective rainfall and relatively short lag times during intense short-term rainfall events. This indicates that during heavy rainfall events, rapid groundwater rise in the bedrock caused by pipe flow from the surface may occur, reaching the surface layer and destabilizing the surface soil. This can be a possible mechanism of simultaneous and multiple debris flows occurrence observed in the heavy rainfall event on July 2018 in western Japan.

DOI: https://doi.org/10.3850/978-90-833476-1-5_iahr40wc-p0847-cd

Year: 2023