Experimental study on debris flow behavior in debris fan area : considering influence of houses

Kana NAKATANI, Megumi KOSUGI, Yuji HASEGAWA, Yoshifumi SATOFUKA and Takahisa MIZUYAMA

Debris flow causes flooding and sediment deposition when they reach debris fan area. Usually, urban development in Japan results in the construction of many houses on debris fan area, and that affects the flow and deposition during flooding. However, few previous studies have considered the effect of houses to disasters associated with debris flow. This study conducted model experiments to determine the influence of houses on debris flow flooding and deposition. We applied uniform sediment, and also applied with coarse grained sediment. We conducted cases without houses; with houses, with houses and fences; and with houses can be destroyed. The model experiments showed that when houses are present, the debris flow spreads widely in the cross direction immediately upstream of the houses. Houses located in the debris fan also influence the deposition area. The presence of houses led to flooding and deposition damage in some places and reduced the damage in others. Especially when fences exist around the houses, flow moved down between the fences; as in the real disaster cases flow moved down towards the roads. When houses destroyed, flow moved down through the destroyed houses; and changes the flooding and deposition process comparing with non]destroyed houses case. With debris flow containing coarse grained sediment, when houses exist, most of the coarse sediment deposited upstream area of the houses.