Landslide Hazard Zonation (LHZ) Around Alemketema Town, North Showa Zone, Central Ethiopia-A GIS Based Expert Evaluation Approach

In the present study landslide hazard zonation (LHZ) was carried out in an area around Alemketema town, central Ethiopia, about 120 km north of Addis Ababa. For LHZ map preparation, GIS based expert evaluation technique was followed. The parameters considered are; slope geometry, slope material, structural discontinuities, landuse and landcover, groundwater, seismicity, rainfall and manmade activities. For landslide hazard evaluation the study area was divided into 273 slope facets and thematic layers on slope facets and intrinsic parameters were prepared in GIS environment from secondary data, topographical map and satellite images. Later, primary data on various parameters was collected facet wise from the field and as per actual observations suitable modifications were made to the thematic maps. Further, geo-processing in GIS environment was done to know the type of parameter classes that fall within each slope facet. Based on the presence of various intrinsic and triggering parameters class within a slope facet, appropriate ratings were assigned to the parameters as per expert evaluation. Later, sum total of all ratings for various parameters form the basis to prepare the LHZ map in GIS. As per prepared LHZ map, 66.9% of the area falls into ‘high hazard zone’ and 33.1% falls into ‘moderate hazard zone’. Validation of this LHZ map revealed that about 80% of past landslides fall within ‘high hazard zone’. This reasonably confirms the rationality of adopted methodology, considered parameters and their evaluation in producing LHZ map.