Susceptibility Investigation of Debris Flow Hazard Using Topographic Index in the Nakhon Si Thammarat, Southern Thailand

Abstract

Nakhon Si Thammarat (NST) is one of the cities in Southern Thailand that is vulnerable to geohazards, such as debris flows, landslides, and flooding, all of which have the potential to cause significant damage to people and property. Several topographic factors could be potential sources of debris flow, including i) a high angle slope of the mountain and ii) a number of mountain-front outlets. Thus, in this study, we used the Frequency Ratio (FR) method to identify and develop the map of debris flow susceptibility area in NST. The topographic indices associated with debris flow activity are analyzed using terrain data obtained from a Digital Elevation Model (DEM) with a resolution of 12.5 meters. The FR was calculated using a combination of ten parameters representing debris flow vulnerable areas, which included: i) slope, ii) aspect, iii) solar radiation, iv) profile curvature, v) plan curvature, vi) topographic wetness index, vii) stream power index, viii) Melton ruggedness number ix) terrain ruggedness index, and x) topographic position index. According to the results, the debris flow susceptibility of NST can be divided into five levels, with high and very high classes found at the Khao Luang Mountain around the center of NST. The eastern and western NST areas were identified as medium and low classes.