Landslide susceptibility along the mountain route 21 in Taiwan

Landslides due to heavy rainfall usually cause not only the interruption of mountain routes but also the loss of life and property. Hence, closing mountain routes may be a necessary measure when rainfall reaches a warning level. The route 21 in Taiwan suffered numerous attacks of typhoon resulting landslide hazards along the route in the past. This research collects data of rainfall and satellite images before and after typhoons for the years of 1996, 2001, 2004, 2008, and 2009. The landslide susceptibility under heavy rainfall along the route will be assessed with the factors including accumulative rainfall, rainfall intensity, inclination of slopes, strength of rock mass, wetness index, and orientations of discontinuities and slope surfaces. The geology, topography, and rainfall conditions are quantified to establish their corresponding indices. With the satellite images to locate historical landslides, the relationship between topographic index and geologic index can be obtained with respect to a certain rainfall index. The maps of landslide susceptibility with respect to various rainfall conditions can be obtained and provide a basis for the management of the route 21 during rainfall.