Rainfall condition triggering subsurface flows spouting from pipe exits in torrent bed material of the Nishinokaito River in Mount Fujiwara, Mie prefecture, Japan

Hirofumi SATO, Takashi YAMADA, Koichi HANADA, Kenji HIRAYAMA and Nozomi HORIUCHI

The hydrological process for the behavior of subsurface flows is not well understood in a torrent bed material during heavy rainfall. To elucidate this process, it is important to understand and predict the debris flow generation mechanism. Herein we report the results of subsurface flows spouted torrent bed materials as well as the occurrence and non�]occurrence conditions in the Nishinokaito torrent, Mount Fujiwara, Inabe�]shi, Mie prefecture, Japan. Several pipe exits were discovered in a torrent bed material. They were emplaced in a sand and gravel layer between 1.0 and 1.5 m below the surface of the torrent bed material. The gravel supported the internal walls of the pipe exits. Subsurface flows spouted when the rainfall intensity exceeded 5 to 7 mm in 10 minutes and the soil water index exceeded 110 mm.