Assessment of landslide susceptibility, semi-quantitative risk and management in the Ilam dam basin, Ilam, Iran

This research is focused on developing landslide susceptibility, risk and management zonation map in the Ilam dam basin, in the west of Iran. For this purpose, all existent landslide locations in the basin (50 landslides) were registered using GPS device and 70% of these points (35 landslides) were used for landslide susceptibility modeling and the rest (15 events) were used to evaluate the model. In order to prepare landslide susceptibility map, eight key factors were used for landslide occurrence such as distance to fault, distance to stream, distance to road, lithology, land use/cover, slope percent, aspect and precipitation derived from the spatial database in Arc GIS 9.3. A hybrid method of logistic regression and Analytic Hierarchy Process (AHP) were respectively used to determine the weight and rate of different factors and their classes. After applying rate to classes of parameters using the AHP method, landslide susceptibility map was prepared by means of logistic regression analysis tool in IDRISI software. The model accuracy was assessed by receiver operating characteristic (ROC) indicator and the pseudoR2 and used as a basis for risk mapping. The landslide risk map was prepared using Varnes equation through combining three maps of susceptibility, vulnerability and the elements at risk. In order to provide the landslide management map, multi-criteria evaluation (MCE) method was used incorporating susceptibility and risk variables. The results suggest the logistic regression and AHP model has high accuracy (ROC= 81.2%, pseudo-R2= 0.32). We found that 39.84, 72.45, and 76.33 km2 of Ilam dam basinare located in the high and very high classes of lands lide susceptibility, risk and management maps, respectively.