Evaluation of landslides process and potential in Shenmu sub-watersheds, central Taiwan

This study compares two sub-watersheds (Chushui and Aiyuzih sub-watersheds) within a single watershed, the Shenmu watershed, which is one of the most active landslide and debris-flow-prone regions of the Taiwan, and investigates the effect of the variation in geological homogeneity and topographical differences on the evolution of landslides. The study analyses a spatial dataset consisting landslide inventory maps of 11 historical events and 17 satellite images spanning 14 years and recommends a methodology of semi-automatic image identification and visual interpretation procedures. The methodology enhances data integrity via the building of landslide inventories based on pre- and post-event maps. A prediction model of the potential landslide areas within the watershed is developed using a combination of environmental factors, causative factors, and the landslide datasets to determine the spatial and probabilistic relationship in landslide activity. The spatial relationships show that landslides are frequent in areas with favorable combinations of causative and environmental factors related to landslide occurrence. Landslides are prevalent on both sides of river courses, and they are the direct suppliers of sediments to the river, leading to sediment-related disasters. Temporally, it is found that typhoon-induced landslides can be subdivided into three distinct time intervals, and the event, which led to the greatest increase in landslide area, can be identified. Furthermore, a verification of the landslide potential map has been conducted for the two temporal periods of pre-1999 Chi-Chi earthquake and from 1999 Chi-Chi earthquake to pre-2009 typhoon Morakot obtaining an overall accuracy of average 80.35%, which agrees well with previous studies. These maps thus obtained can be used as reference information for decision-making to forecast the occurrence of future landslides and for improving early warning systems and rapid response mechanisms.