Evaluation of landslide occurrence using hydrological model in Huai Nam Phung Subbasin, Thailand

Huai Nam Phung subbasin, which is located at the boundary between Loei and Phetchabun provinces, is the area where landslides occur frequently. Therefore, this study aims to evaluate the occurrence of landslides in this area by using the Digital Elevation Model (DEM), Meteorological data hydrological data and physical properties of soils processed with the Geographic Information System (GIS) to analyze the physical data of the study area and use the TOPography based hydrological MODEL (TOPMODEL) combined with the theory of factor of safety in slope stability to simulate the slope stability between 2016 and 2017. According to the satellite imageries and field survey, there were 63 shallow landslide points. These points have the slope higher than 20 degrees and the landslides at these points occurred in 2017. The model simulation shows that the volume of accumulated water in 2017 was much higher than in 2016. The volume of water was in accordance with the meteorological and hydrological data. From the calibration of parameters in the TOPMODEL, there are 3 most sensitive parameters, the logarithm of areal average of saturated soil transmissivity (lnTe), surface hydraulic conductivity (k0) and capillary drive (CD). From the analysis of slope stability, the slope became unstable from high slope areas and the instability expanded to lower slope areas. Most of becoming unstable of landslide points occurred in July 2017 and the unstable areas were highest on 30 October 2017. From the analysis of slope stability in areas with a slope higher than 20 degrees on that day, there were 4 sub-catchments that most of the areas were unstable, Huai Nam Ko (92.49%), the upper part of Huai Nam Phung (90.14%), Huai Nam Hia (89.97%), and Huai Nam Krang (87.38%). These sub-catchments were located on the areas of the mountain ranges in the northern and western parts of the study area. Moreover, it is found that consecutive heavy rain over a long time can cause the slope to become unstable and immediate heavy rainfall events can also cause the slope to become unstable immediately. This instability can lead to landslide occurrence. In addition, the author created a landslide susceptibility map of the Huai Nam Phung subbasin from slope stability on 30 October 2017 to be a way to cope landslides in the future.