Susceptibility Investigation of Debris Flow Hazard Using Topographic Index in Phang-nga province, Southern Thailand

Abstract

Phang-nga, a province in Southern Thailand, is highly susceptible to geohazards such as debris flows and flooding, both of which pose significant risks to human life and property. Several topographic factors contribute to the potential for debris flow, including: i) steep mountain slopes and ii) the presence of multiple mountain-front outlets. In this study, the Frequency Ratio (FR) method was used to identify and generate a map of debris flow susceptibility across Phang-nga. Topographic indices related to debris flow activity were analyzed using terrain data obtained from a 30-meter resolution Digital Elevation Model (DEM). The FR was computed by integrating ten parameters that characterize areas prone to debris flow, including: i) slope, ii) elevation, iii) aspect, iv) lithology, v) vegetation cover, vi) land use, vii) topographic wetness index, viii) terrain ruggedness index, ix) rainfall, and x) profile curvature. The findings indicate that debris flow susceptibility in Phang-nga can be categorized into five levels. The high and very high susceptibility classes are concentrated in the valley directions, near the streamlines. The most prevalent class in the region is the moderate susceptibility class. Meanwhile, the eastern and southern parts of Phang-nga have been found to have low and very low susceptibility (Class 1 and Class 2, respectively), located in the direction of the mountain range and areas with lower average rainfall.