天然ダム越流による侵食と土砂流出の実態 ： レーザープロファイラを用いた解析

抄録

Landslide dams induce catastrophic outburst floods or debris flows mostly by overtopping. However, adequate information about sediment transport of landslide dam and changes of grain size distribution due to overtopping are still lucking. The 2008 Iwate and Miyagi inland earthquake triggered 15 landslide dams. Here we showed new data about the sediment transport of two landslide dams occurred by The 2008 Iwate and Miyagi inland earthquake due to overtopping erosion by the LiDAR data. We measured at 3 times, before overtopping erosion (just after the earthquake), after the overtopping erosion, around 4 mouths after the overtopping erosion). We found that about only 1/2～2/3 was eroded by the overtopping among the height of a landslide dam, and the water channel is formed in overtopping erosion ; it had indicated that the water channel is wide in the downstream more than upstream. One side a part of the sediment from a landslide dam has deposited between landslide dam and small-scale landslide dam in the downstream, and the longitudinal riverbed gradient approaches to initial gradient. In addition, after overtopping erosion once, the substantial change was not seen in the shape of a landslide dam though there was a rainfall of the total about 120 mm.