LANDSLIDE SUSCEPTIBILTY ASSESSMENT USING GIS MODELING - THE CASE STUDY OF ZOMBA MOUNTAIN AREAS

Landslide susceptibility mapping is a practical tool in natural and urban planning. It can be applied for determining land use zone, in construction design, and planning of a variety of projects. In this study, GIS based landslide susceptibility map were generated in the mountainous parts of Zomba district at the Southern part of Zomba Mountain plateau which has helped in determining the slope effects that can induces landslides in the study area. This was accomplished by using the weight of evidence (WoE) method for correlating the causative factors which have an effects on landslide occurrences.
The instability factors taken into account were lithology, slope angle, slope aspect, distance to stream, curvature and land use. These factors were integrated in GIS environment for constructing the thematic layers of factor dataset. For this bivariate statistical approach, significant assumptions were emphasized prior to the study to establish conditional independence between each pair of components. In addition, a detailed landslide inventory map was constructed through field investigation and Google earth image interpretation process at a scale of 1:125,000. The thematic layers and landslide map were overlapped to obtain a spatial statistical relationship. The produced susceptibility map were classified into four zones: Very Low, Low, Moderate, and High susceptible zones and validated using the other half number of the landslide events of the area. The map indicates that more than 90% of the landslides were in categories of high and moderate susceptibility zones. The causative factor classes including the slope class >55, the north facing slopes, the highly weathered Syenites and superficial deposits of Dambo soils and the bare lands were identified to considerably influence the landslide in the study area.