Hydrological model of landslide risk in Huai Nam Phung subbasin, Thailand

Landslide is one of water-related disasters which occurs frequently in Thailand. However, studies of landslides related to hydrological models in Thailand were still limited. Therefore, this study applied the hydrological model to evaluate occurrences of landslides in Thailand. The study area was Huai Nam Phung Subbasin, where there were 63 shallow landslides found during 2016–2017. A temporal change of groundwater level was calculated from meteorological data by TOPography-based hydrological MODEL (TOPMODEL). After that, slope stability safety factors at different times and locations were calculated from the groundwater levels and physical characteristics of the area. The results reveal that the landslides occurred in 2017 rather than 2016 due to high volume of water in that year. The slopes became unstable in steep slope areas, and this instability extended to gentler slope areas when more water accumulated. According to the slope stability on 30 October 2017, the day with most unstable areas during the study, all of the 63 found landslides were in the unstable areas. On that day, there were 7 mountainous sub-catchments where more than 80% of the slopes were unstable. Most of the unstable areas were in the western part of the study area. Both consecutive heavy downpours over a long period of time and individual heavy downpours can cause slopes to become unstable. The finding of this study suggests that landslide early warning systems are required for the steep slope areas in the Huai Nam Phung Subbasin and the hydrological data should be monitored for the warning.