Little is known about the actual situation of torrent bed scouring]induced debris flow generation, despite developing theoretical and experimental research. Herein we report subsurface flows discharged and spouted from cross]section of torrent bed material as well as overland flow generation by debris flow occurrence using an automated interval camera installed at the No.6 Sabo Dam construction site in the Nishinogaito torrent, Mount Fujiwara , Inabe]shi,Mie prefecture, Japan.
Subsurface flows spouted from cross]section of torrent bed material during heavy rainfall, and their volumes increased as the amount of rainfall increased. In addition, a lot of sediment spouted from several holes created at cross]section of torrent bed materia with a subsurface flow prior to debris flow. Serial camera]footage analysis revealed a time difference between overland flow and debris flow. Subsurface flows may travel in several pipes developed in debris flow deposits, and water can concentrate in pipes during heavy rainfall, resulting debris flow generation.

Key wordsFcross section of torrent bed material, subsurface flows, overland flow, camera footage]analysis