Remote sensing and GIS-based mapping on landslide phenomena and landslide susceptibility evaluation of Debresina Area (Ethiopia) and Rio San Girolamo basin (Sardinia)

The thesis presents GIS based spatial data analysis for landslide phenomena and susceptibility mapping which is carried out in Debresina area of the Afar rift margin (in Ethiopia) and in Rio San Girolamo basin at the margin of Campidano graben (in Sardinia, Italy). Both of these distant study areas are prone to various types of landslide and landslide-generated hazards with tremendous damages such as loss of human lives, failure of infrastructures, and damage on agricultural fields and on the natural environment. Landslides and related hazards have no geographic boundaries. They occur in both developed countries (like Italy) and in developing countries (like Ethiopia) causing a continuous threat to human beings all over the world. The objectives of this study in both project areas were therefore: (1) to generate maps of landslide inventory and various landslide causative factors, and evaluate their contribution to the occurrences of landslide and its frequency in the respective study areas, (2) to evaluate the landslide susceptibility and prepare maps of both study areas using various GIS based methods and compare their results, (3) to recommend landslide hazard mitigation strategies based on the final findings of the study for both respective project areas. The study accomplished:(1) characterization of 160 and 108 landslide occurrences in Debresina and R.S.Girolamo areas respectively (2) remote sensing and field investigations of the landslide causative factors (3) laboratory investigations of some physical, mineralogical and geotechnical properties of rocks and soils, and (4) GIS-based data analysis and landslide susceptibility evaluation using Overlay Mapping (OM), Frequency Ratio (FR), Analytical Hierarchal Process (AHP) and Global Limit Equilibrium (GLE) methods. Besides, methods like the Kinematic Analysis and Melton Ratio are also applied to further appraise the effect of geological structures in the Debresina area and to identify the type of debris flow, debris flood and normal flood in the R.S.Girolamo respectively. Though the utilized landslide causative factors vary depending on the applied methods and the specific condition of the study areas, a total of seven landslide causative factors such as lithology, proximity to faults and to drainages, land use, slope, aspect and elevation were selected and prepared in GIS for landslide susceptibility mapping in the Debresina area. Six similar causative factors are also used at the R.S.Girolamo area excluding proximity to fault. Results of the study revealed that: (I) the major final triggering factor for the September 2005 landslide event of Debresina area is most probably earthquake besides to the saturation and active gully erosion while in R.S.Girolamo are rainfall and active gully erosion (II) More than 77% of the landslide occurrence in Debresina area is contributed by complex/composite slide and debris/earth slide while about 75% landslide occurrences in R.S.Girolamo is covered by debris flow (III) all the methods (OM, FR and AHP) more or less give similar V Remote Sensing & GIS-based Mapping on Landslide Phenomena & Landslide Susceptibility Evaluation of Debresina area (Ethiopia) & R.S. Girolamo basin (Sardinia) indication that an area is susceptible to slope failure in Debresina area if it is covered by lithology of colluvium-eluvium, debris deposits, various tuffs and clay soils, have slope range of 10°-40°, land use of river course, arable and bare rock, have proximity to fault of 0-600m and to drainage 0-300m, have elevation of 2000-2500m and with an aspect to East and Southeast. Whereas the R.S. Girolamo area is prone to landslide if it has a lithology of alluvium, talus, granite and colluvium; have a slope class >260, have land use of river coarse, forest and bare rock, have proximity to drainage of 0-100m, with elevation of 450-600m and having an aspect of facing North, Northwest, Northeast and Southward (IV) the top landslide causative factors in Debresina area are lithology (34.2%), proximity to fault (24.5%), proximity to drainage (16.2%) while in the R.S. Girolamo the main landslide influencing factors are proximity to drainage (41%), lithology (24%) and land use (13%), (V) the prediction accuracy of the OM, FR and AHP methods in both study areas is compared based on Area under the Curve (AUC) method and results verified that the percentage of prediction accuracy of the methods in general is higher at the Debresina area than in R.S.Girolamo. This could be mainly attributed to the prevalent landslide types in each study areas. Hence, it can be suggested that the applicability of these methods for the susceptibility analysis flow-like landslides (e.g. debris flow) and rock falls/topples are relatively lower than in the other types of landslide types (VI) in the GLE method of circular failure surface, the reduction of the SF from the dry slope to the saturated slope condition for the Debresina area is 43-45%, but in the case of R.S.Girolamo the reduction of SF reaches up to 64-71%. This evidenced that the triggering impact of water for slope failure is greater in R.S.Girolamo than in Debresina area (VII) the overall study results of the various methods presented in this thesis have shown the great potential of GIS-based landslide predictions and can therefore be used as a basic data for preliminary slope management and land-use planning of the respective study areas. The state of prevention towards the hazards is quite different in both areas, owing to the developmental difference of the two countries, Ethiopia and Italia. Thus, in R.S.Girolamo landslide and related hazard prevention measures are better institutionalized and, hence, with better territorial management and public awareness of the hazard. Whereas in Debresina area, no responsible institution exists to date and the territorial management is poor, and people have no idea how to prevent landslide hazards. Based on the obtained susceptibility maps and considering the economic, cultural and technological differences of the two study areas, landslide hazard mitigation strategies and remedial measure options are recommended.