A Numerical Hazard Rating Method for Debris Slide Susceptibility Mapping in Turkana, Kenya

This study presents a numerical rating method for mapping debris slide susceptibility in Turkana, Kenya. The use of remotely sensed data; 31 m digital elevation model (DEM) 1.5 m SPOT 6 image of study area, and an exploratory soil and agro-climatic zone map of Kenya, (1:1,000,000) were adopted. Numerical hazard rating scheme for testing relationship between debris slide and five event controlling parameters; slope angle, friction angle of soil, soil drainage, soil thickness and proximity to drainage is described. Corresponding thematic data layers were generated for these parameters in ArcGIS. Numerical hazard ratings were assigned to these parameters on a scale of 0 – 5 with 0 being the least susceptible class and 5 having the greatest susceptibility to debris slide. These hazard ratings were justified with the use of the Coulomb Equation of stability analysis. Debris slide susceptibility map indicates that areas close to drainage channels had the highest susceptibility value ranging from 3 – 5. On the hand, areas with no surface material, i.e., bedrock outcrop, and low slope angles had minimal susceptibility value of zero (0). There was no landslide data for the study area and hence the debris slide susceptibility map could not be validated. This study therefore has developed a method for debris slide susceptibility assessment that can be adopted in an inaccessible terrain, or in an environment with no landslide data.