Susceptibility investigation of debris flow, landslide and flood hazards using topographic index in Nakhon Si Thammarat province

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. To identify hazard susceptible areas, terrain analysis techniques based on a Digital Elevation Model (DEM) with a resolution of 12.5 meters were used in this study. The Statistical Index (SI) was applied in relation to six parameters to indicate landslide-prone areas. Meanwhile, the Frequency Ratio (FR) was analyzed in relation to ten parameters to indicate debris flow susceptible areas. The Hydromorphometric Contrast Index (HCI) was used to define flood-prone areas by evaluating five parameters. According to the result, the landslide susceptibility map can be classified into five levels. The western mountains of Nakhon Si Thammarat were found to have high and very high susceptibility. Additionally, the debris flow susceptibility in this area can be divided into five levels, with the high and very high classes discovered in the Khao Luang Mountain around the center of Nakhon Si Thammarat. Furthermore, the study's findings on flood susceptibility can be classified into four levels. The highly sensitive areas were found in the central part of Khanom district in Nakhon Si Thammarat. The receiver operating characteristic (ROC) curve was used to validate the accuracy of the results. The results revealed that the area under the curve (AUCs) for the Si, Fr, and HCI methods are 56.6%, 43.5%, and 98%, respectively, indicating a practically identical predictive capacity.