Discover failure mechanism of a landslide dam using UAV Kuo-Lung Wang 1 and Zhi-Jie Huang 2 1) Associate Professor, Department of Civil Engineering, National Chi Nan University, Nantou, Taiwan. Email: klwang@ncnu.edu.tw 2) Master, Department of Civil Engineering, National Chi Nan University, Nantou, Taiwan. Email: klwang@ncnu.edu.tw Abstract: Unmanned Aerial Vehicle (UAV) was developed very fast in recent years and budget to use UAV was reduced very fast. Thus the usage of UAV for investigation is becoming possible and using as a basic tool. Road Tai-14 at 74.5K is selected as study area in this research. A landslide dam was formed in 0610 heavy rain fall event in June, 2012. The landslide dam was collapsed in few hours and foundation of road was destroyed by erosion with fast water flow, which resulted in closed roads closed for several days. Current slope condition was analyzed from temporal satellite images, field investigation, and high resolution orhtophotos, high accuracy DSM from UAV. The result shows that the landslide dam in 2012 was formed from the landslide located at right bank of river. Moreover, the slope is still not stable and moving in 2014 without heavy rainfall event. More geological formation is discovering from high resolution orthophoto and DSM. The results show that the landslide was induced not only by rainfall but also geological structure failure. So continuous monitoring should be carried on in this study area. Keywords: UAV, landslide, orthophoto, PIV 1. INTRODUCTION The study site, where is Ren-Tzu-Guam located central of Taiwan and a shaped sandstone canyon scenery cut by May river as shown in Figure 1. Sand rock in this area is stiff and formation almost vertical. According to fossil record by Hsieh(2011), the study is located at the bottom of Lushan formation. Landslide was occurred owing to heavy rainfall from 10 to 12, June, 2012. According to interview and police documentation, landslide dam was formed and flushed away in 2 hours in the morning of 12, June, 2012. Landslide located at 75k of Road Tai-14 and the road was blocked owing to one lane of the road was destroyed by landslide dam break. According to previous study of authors, the landslide dam event was sliding again form the rest of slide mass occurred in 2008 event, typhoon Sinlaku. Figure 1. Location of study area However, the geological formation of study site is slate, Lushan formation according to Wushe geological map (scale 1:50,000). Major geological bedding is N42E/80SE but also consists of N12E to N43E/ 10 to 25 SE cleavage. Bedding and cleavage interlayered horizontally and vertically during field investigation. The geological condition is squeezed and fractured with Meishi fault located nearby. Unmanned Aerial Vehicle (UAV) is adopted in this 1494