Landslide hazard evaluation and zonation in and around Gimbi town, western Ethiopia-a GIS-based statistical approach

The main purpose of the present study was to carry out landslide evaluation and zonation in and around Gimbi town in western Ethiopia, located about 440 km from Addis Ababa. This study was conducted following GIS-based statistical method. For hazard evaluation and zonation, nine causative factors viz., slope material, elevation, slope, aspect, curvature, groundwater surface traces, distance to roads, and distance to streams were considered. Data on these causative factors were obtained from secondary maps, digital elevation model, topographical sheets, and through field mapping. Fifty past landslides in the study area were also identified and mapped through field survey and image interpretation. Statistical correlations between each of the causative factors and the past landslides were established in GIS environment to rate the relative contribution of individual factor classes. Thus, by considering ratings for each causative factor subclasses and by assigning suitable weights to each factor, random trial combinations were attempted to produce the landslide hazard zonation map. The results showed that 12.2% of the study area falls in very high hazard, 30.7% in high hazard, 24.3% in moderate hazard, 23.3% in low hazard, and the remaining 9.5% in no hazard zones. Validation of landslide hazard zonation map with past landslides showed that 75% of the past landslides fall within very high and high hazard zones. Thus, the hazard zones depicted can be considered for future planning and development of the study area.