Experimental study on landslide dam formation process and outburst caused by head slope of Inari-gawa : using large scale model experiment

Yuji HASEGAWA, Nobuo SUGIURA, Tateo MITSUNAGA, Isamu SATO and Takahisa MIZUYAMA

It is known that large]scale landslide dam is often formed by landslide due to heavy rain or strong earthquake. On the other hand, landslide dam formation caused by sediment runoff is not known well. Especially sediment transportation from head stream of the mountain is unclear, and it is not certain that landslide dam can be formed in this area. In upstream area, large sediment may flow down even flow depth is small. In that case, it is not clear that how sediment moves; it may be because of fluid force pushing the sediment or it may be the sediment movement. Same thing can be mentioned when sediment stops moving. Furthermore, flow through the stopped large sediment may cause collapse due to soil infiltration, or sediment may flow down by erosion due to surface flow; the phenomena is quite complicated. Therefore, we constructed large scale model experiment facilities for Inari]gawa basin, and conducted experiments. Results showed that large]scale landslide dam can be formed due to sediment runoff from the upstream area. However, it cannot occurs in every stream, it appeared because Inari]gawa basin has characteristics of landform (e.g. curve, confluence, waterfall, and large rocks in the river channel) and sediment conditions (e.g. wide range distribution of sediment, 2m diameter rocks can be included). Landslide dam formed in confluence point collapse scale changed when runoff time is different from the both branches.