Landslide hazard investigation in Changwat Nan

Abstract

The Nan province in northern Thailand was selected for landslide hazard investigation because there was a series of landslides in August 23, 2006 that damaged properties and lives. The investigation is aimed to evaluate the susceptibility or hazard mapping of landslides in the Nan study area using remote-sensing interpretation and geographic information system (GIS). Landslide locations or scars were identified in the Nan study area from interpretation of aerial photographs as well as enhanced Landsat 7 ETM and IKONOS image for constructing the scar map. Then several factors affecting landslides, including elevation, slope, landuse, lineaments and lithology were identified and displayed as maps using GIS. Later, landslide assessment was done using bivariate probability method and followed by weighting analyses of involving factors. The results indicates that the open-forest areas dominated by the steep slopes, sandstones / tuffaceous rocks, proximal long faults / fractures, are prone to landslide hazard. Subsequently, degrees of landslide hazards were expressed as very low to very high hazard levels. The result is shown as a landslide hazard map with a satisfactory cross validation agreement. The outcome map also indicates that high- to very high- level hazard areas are the mountainous areas in Chalerm Prakiat, Song Khwae, Chiang Klang and Pua Districts. Several districts, such as Na Noi, Wiang Sa and Nan in the southern part of the Nan study area have much lower hazard level.