LANDSLIDE HAZARD ASSESSMENT ON SLOPES IN TWO CITIES IN NORTHEAST BRAZIL USING THE SHALSTAB MODEL

Abstract

The cities of Ilhéus and Itabuna, located in the southern region of Bahia, present favorable conditions for landslides due to their natural attributes and the unplanned occupation of hillslopes. This study aims to assess landslide susceptibility (hazard) in these cities using the Shallow Landsliding Stability Model (SHALSTAB). A physical-environmental assessment of the study areas was conducted, including the compilation of a landslide inventory and its spatial distribution, the implementation of the SHALSTAB model, and the analysis of susceptibility and its relationship with rainfall events. The assessment successfully identified the most susceptible areas in Itabuna and Ilhéus. Among the instability classes defined by the model, the unconditionally unstable unsaturated class was the most significant, being more prominent in Ilhéus due to prevailing geomorphological conditions. The model results were confirmed by the landslide inventory, which showed that landslides were located on or near the most unstable slopes. According to SHALSTAB, rainfall between 0 and 30 mm/day is sufficient to trigger landslides in many of these unstable areas. However, the vast majority of landslides in these cities were triggered by precipitation volumes greater than the range defined by the model.