[M-IS15] Geophysical particulate gravity current

[MIS15-P03] Investigation of behavior of debris flow with driftwood by dam-break experiments

Teruki Izawa¹, *Yuichi Sakai¹ (1.Faculty of Agriculture, Utsunomiya University)

Keywords:Debris flow, Driftwood, Dam-break experiment

In recent years, when debris flows occur in Japan as a result of heavy rainfall, the damage caused by the resulting driftwood has increased. This is partly due to the fact that trees in Japanese forests are becoming larger in diameter and forest accumulation is increasing. From the viewpoint of disaster prevention, there is a need to understand the behavior of mudslides mixed with driftwood. Among various factors that contribute to the generation of driftwood, standing trees generally become driftwood when landslides become debris flows. Although many studies have been conducted on the behavior of debris flows with driftwood, the process by which debris flows with driftwood are generated from hillslopes with standing trees has not been adequately investigated. In this study, a dam-break experiment was conducted to investigate the process of converting standing trees to driftwood by generating debris flows.

In the experiment, a channel corresponding to a stream section with 15° slope and a channel corresponding to a slope section with 45° slope were prepared. After saturating the deposited sediment with water, the shutter holding it were opened to generate a debris flow by dam break, and the behavior of sediment and driftwood as they flowed into the stream section was examined. As experimental conditions, four different confluence angles between the stream and slope sections were set from 0° to 90°, two different deposited sediment layer thicknesses, and three different water supply methods after saturation of the deposited sediment were varied. The results showed that the behavior of the driftwood basically followed that of the sediment and was accordingly affected by the confluence angles.