Japan Geoscience Union Meeting 2016

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International Session (Poster)

Symbol H (Human Geosciences) » H-TT Technology & Techniques

[H-TT08] Geoscientific applications of high-definition topography and geophysical measurements

Sun. May 22, 2016 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall HALL6)

Convener:*Yuichi S. Hayakawa(Center for Spatial Information Science, The University of Tokyo), Hiroshi, P. Sato(College of Humanities and Sciences, Nihon University), Shoichiro Uchiyama(National Research Institute for Earth Science and Disaster Prevention), Shigekazu Kusumoto(Graduate School of Science and Engineering for Research, University of Toyama), Thad Wasklewicz(East Carolina University), Daniele Giordan(National Research Council, Rome), Hiroyuki Obanawa(Center for Environmental Remote Sensing, Chiba University)

5:15 PM - 6:30 PM

[HTT08-P05] Using an unmanned aerial vehicle to examine influence of topography on development of debris flows in a initiation zone of Ohya landslide, Japan

*Haruka Tsunetaka1, Norifumi Hotta1, Fumitoshi Imaizumi2, Yuichi S. Hayakawa3 (1.Faculty of Life and Environmental Sciences, University of Tsukuba, 2.Faculty of Agriculture, Shizuoka University, 3.Center for spatial Information Science, The University of Tokyo)

Keywords:Debris flow, Deep-seated landslide, SfM-MVS, UAV

In debris flow initiation zones, flows alter the topography of deposited sediments through their development by entrainment. Although it is possible that such topographic changes influence the magnitude of subsequent debris flows, this influence is not well understood because of the difficulty in conducting a temporal series of high-definition topography measurements. Therefore, to examine how topography affects the development of debris flows, we carried out structure-from-motion (SfM) photogrammetry from aerial shoots by an unmanned aerial vehicle (UAV) in the Ichino-sawa subwatershed of the Ohya landslide, in central Japan. Debris flow occurrences and rainfall were monitored using interval cameras and a rain gauge. In the gully in the hillslope, the sediment discharge was dominated by entrainment due to the deposited sediments that were gradually discharged by storm rainfall events. In comparison, deposition several meters thick typically occurred in the main channel. Consequently, the topographic changes in the main channel were more complex than those of the gully. Furthermore, in the main channel, the trends in the changes regarding the amount of sediment differed in the upper and lower parts of the confluence of the gully. In the upper part of the main channel, sediment entrainment and deposition occurred repeatedly after each debris flow, whereas entrainment by such flows dominated the topographic changes in the lower part. Consequently, deposited sediment supplied by a previous debris flow in the upper part contributed to the development of the subsequent debris flow. The results indicate that the magnitude of the debris flow was affected by the topography of the main channel created by previous flows, including flows from the gully.