2. Application of Remote Sensing and GIS for Landslide Disaster Management: A Case from Abay Gorge, Gohatsion–Dejen Section, Ethiopia

The Abay Gorge, along Gohatsion–Dejen road, in Ethiopia witness frequent landslides during the rainy season. The natural stability of slopes has been disturbed due to the road construction, the fragile geological conditions, groundwater and uncontrolled surface run-off which favor landsliding during rainy season. Such landslide hazard has resulted into frequent disruption in traffic movement and endangered the people life and their property in the area. Rock fall, toppling, debris slide and rotational failure of colluvial material are some of the common land instability manifestations observed in the area. Mitigating landslide risk disaster is of prime concern and through the present study attempts are made to delineate the landslide hazard prone zones in the study area. For this purpose Landslide Hazard Zonation (LHZ) mapping using integrated Remote Sensing and GIS technique was carried out so as to classify the land surface into zones of varying degree of hazard. Thus, the landslide hazard zonation mapping produced through present study will be useful to the planners and engineers to know the zones which are prone for landslide disaster and they may evolve suitable remedial measures for disaster risk reduction and management.

For the present study, “Weighted Linear Combination (WLC)” technique was used to prepare the Landslide hazard zonation map. In WMC technique, each factor was multiplied by its derived weight and later the results were added to produce the landslide hazard map.

WLC helps to handle the problem of integration of different data layers with heterogeneity and certain degree of uncertainty. The method used is very useful to integrate single factor maps with each other and thus to produce a multi-thematic map. This model requires multi spatial data on a target area and then can be extrapolated in to a larger area as required. For landslide hazard zonation the major event controlling parameters which were considered are; geology, groundwater conditions, drainage, slope, geologic structure, aspect, and land use/land cover.

For landslide hazard zonation five relative classes, namely Very Low Hazard (VLH), Low Hazard (LH), Moderately Hazard (MH), High Hazard (HH) and Very High Hazard (VHH) were considered. The result has shown that out of 21 past slope failures, seven (33.33 %) occurs in very high, seven (33.33 %) in high, five (23.81 %) in moderate and two (9.52 %) in low hazard zones, respectively. The comparison shows satisfactory results as 67 % of the past landslides lie within the maximum hazard zone, and the remaining within the moderate and low hazards zones. No landslide event was observed in the very low hazard zone. Thus, the satisfactory agreement confirmed the rationality of the considered governing parameters, their influential weight, the adopted methodology, tools and procedures in developing the landslide hazard map of the study area.