The construction of a large dam implies a number of environmental changes and the accurate study of the rock mass foundation. Besides the aspects related to the foundation, the geologic and geotechnical characteristics of the reservoir area gained increasing importance due to the possibility of slope instability which might, eventually, affect the serviceability of the dam. Effects can be felt both upstream and downstream and therefore an accurate geological mapping is obligatory to understand and preview susceptibility to accidents.
Slope instability in rock masses is a complex phenomenon that can be manifested by different types of mechanisms often controlled by the geologic structure, namely the joints system. Changes in the existing stress state can lead to modifications in the slope morphology which tend to find a new equilibrium profile. The present work presents the geological mapping performed in the area covered by the reservoir of a large dam to be built on a rock mass composed of metasedimentary rocks. In order to assess the stability of the reservoir slopes, the geotechnical assessment included desk study and field survey, as well as the use of digital elevation modelling (DEM) in order to obtain a set of susceptibility factors maps. These included the geological map of the area, altimetry, slope angle maps, slope strikes and land use mapping complemented with stereographic projection of the joint system in different location for kinematic analysis. The combination of susceptibility factors led to the identification of areas where landslides can potentially occur based on weights of different susceptibility factors.