Landslide Susceptibility Evaluation on Agricultural Terraces by the Application of Physically Based Mathematical Models

Abstract

This paper focuses on the evaluation of landslide susceptibility in agricultural terraces, in the Douro Region, with earth embankments, using two physically based models: SHAllow Landslide STABility model and Stability INdex MAPping. The applied models combine an infinite slope stability model with a steady state hydrological model. Both susceptibility models use the following soil properties parameters: cohesion, friction angle, soil specific weight and thickness. The SINMAP also uses the root cohesion. Besides the different mathematical formulas applied on each susceptibility modelling, the definition of the contribution areas in the hydrological model is based on different algorithms. The SHALSTAB uses the Multiple Flow Directions (MFD) and the SINMAP uses the Deterministic-Infinity (D∞). The results validation is made with the inventory of past landslides, done through the contingency table method. This procedure shows that SHALSTAB classifies 77% of the landslides on the susceptibility areas, while SINMAP reaches 90%. Simultaneously, the SINMAP model presents a very high False Positive Rate (83%) against significantly lower values of False Positive Rate (67%) for SHALSTAB. The relation between True Positive Rate and False Positive Rate is better for SHALSTAB (1,14) then for SINMAP (1,09) showing a better balance between prediction capability and delineation of unstable area.