Experimental study on debris flow deposit dam formation and outburst process

Yuji HASEGAWA, Kana NAKATANI, Yoshifumi SATOFUKA and Takahisa MIZUYAMA

Recently, it is reported that debris flows with woody debris cause damage. For example, jamming at bridges causing high water levels and flooding, or leading sudden high flow depth surges at downstream when blockaded woody debris break away from temporarily building structures and standing trees. This study is based on a flume experiment focus on how the woody debris causes or enlarges above mentioned phenomena. To investigate the woody debris factor, such as the shape and provenance of the wood, debris volumes and water flow, authors used hydraulic models that reproduced actual landforms. The main findings are as follows. (1) Debris woods accumulated when logs carried along by debris flows passes from forest area, then debris woods move in frontal part of the debris flow, and the flow with water and sediment follows. This causes temporary blockages on bridges in mountainous rivers. (2) The peak discharge that occurs after the blockages collapse is around 1.2 times higher than debris flow without blockage collapse.