[H-DS07] Landslides and related phenomena

[HDS07-15] Runout characteristics of debris flow under the effects of ground freezing on Mt. Fuji

*Fumitoshi Imaizumi¹, Ren Yamamoto², Atsushi Ikeda³ (1.Faculty of Agriculture, Shizuoka University, 2.Graduate School of Integrated Science and Technology, Shizuoka Univeristy, 3.Faculty of Life and Environmental Sciences, University of Tsukuba)

Keywords:debris flow, seasonally frozen ground, bed deformation

Debris flows are one of the most destructive sediment transport processes in mountainous areas because of their large volume, high velocity, and kinematic energy. To clarify temporal changes of debris flow characteristics in cold regions, river bed deformation caused by debris flow was evaluated in Osawa creek on Mt. Fuji, Japan. We conducted field monitoring of the ground temperature to estimate the presence or absence of seasonally frozen ground during historical rainfall events. Bed deformation along the debris flow torrent was assessed by analyzing airborne LiDAR DEMs (total 18 periods), which was constructed in the period from 2008 to 2020. In the periods without frozen ground, aggradation of channel bed was evident even in steep channel sections. In the periods with frozen ground, channel gradient with active degradation and aggradation was different amongst debris flow events affected by rainfall characteristics. Degradation was predominant throughout the channel during the rainfall events with high total rainfall depth, while aggradation was predominant during the rainfall events with low total rainfall depth. The results suggest that the occurrence of frozen ground affects debris flow behavior in cold regions.