Field experiment of deformation processes of a landslide-dam in the Ashiarai Basin

Norio HARADA, Fumiaki AKAZAWA, Satoshi HAYAMI, Go YANAGISAKI, Yoshifumi SATOFUKA,
Masamitsu FUJIMOTO, Daizo TSUTSUMI and Syusuke MIYATA

The study of landslide dam deformation is important for predicting potential floods, and in the implementation of effective flood]risk management. To understand the deformation processes of landslide dams, and the outflow discharge characteristics under conditions similar to those of an actual landslide dam, we carried out experiments on a landslide dam in the mountainous streambed of the Ashiarai Basin. The results of previous field experiments suggest that the dam height, reservoir volume, and deformation processes influence the outflow discharge; however, the effects of the scale of the dam in previous experiments were unclear, and the scale of the dam is expected to be significant. For these reasons, our experiments, which were performed in July 2014, were carried out using a larger]scale dam. We carried out preliminary small]scale experiments to identify potential problems prior to carrying out the large]scale experiments. Here we report the results of the preliminary experiments and the large]scale field experiments. In the field experiments, pipes were laid on the riverbed to drain water from the dam reservoir, and a dam was constructed under dry conditions. During the preliminary experiments, a large quantity of water was drained via infiltration around the pipes, and water was not stored. To address this, we stopped the infiltration of water around the pipes using sandbags and putty. In the large]scale field experiments, dam deformation resulted from erosion due to overtopping. We observed dam deformation processes, outflow discharge, and the water level inside the dam. The resulting measurements of the water level inside the dam showed that part of the dam was unsaturated during deformation. The results of the deformation and outflow discharge processes show that the erosion width increased with increasing outflow discharge. The results of the outflow discharge were compared with those of previous experiments.