Landslide susceptibility assessment of Calabar, Nigeria using Geotechnical, Remote Sensing and Multi-Criteria Decision Analysis: Implications for urban planning and development

This research was carried out to delineate zones of high likelihood of landslide occurrence in view of the fatal incidence of September 2013 that buried a building and 9 occupants in the city area of Edim Otop. Method involved field geotechnical boring and laboratory analysis; remote sensing analysis of SRTM-(DEM) and Landsat ETM imageries to extract slope and aspect; land use land cover, drainage and normalized vegetation index. The zonation of landslide susceptible areas was implemented using analytic hierarchy process (AHP) in a multi criteria decision analysis of factors important in landslide occurrence. Results of the AHP depicts that the ground slope contributes 32% to the likelihood of landslide occurrence, while the orientation of the slope (aspect), soil type, cohesion, friction angle, hydraulic conductivity, drainage, land use land cover and normalized vegetation index's causative abilities to slope instability, failure and landslide susceptibility were 22%, 16%, 9%, 7%, 6%, 3%, 3%, and 2% respectively. Three landslide susceptibility zones of low, high and very high landslide susceptibility have been delineated. The ten deep gully sites sampled during the field studies all fall under the zone of very high land slide susceptibility including Edim Otop, the site of the September 2013 fatal rainfall induced incidence. Recommendations for management include risk and hazard quantification considering human occupation on very high landslide susceptibility areas, slope protection methods including excavated sections, use of sites of previous landslide such as Edim Otop as pilot projects to characterize the mechanism of slope instability and back analysis of slope failure as reference.