Methodology for landslide risk assessment – a case study of the Poroj River catchment area

Abstract The article presents basic elements of methodology for landslide risk assessment applied for a case study of the Poroj River catchment area in Macedonia. This region is known as very vulnerable and susceptible to landslide, erosion and flood phenomena, with high level of risks over affected population and infrastructure. Main elements of risk assessment are related to: preparation of shallow landslide susceptibility models, calculation of slope stability and probability of failure of large deep landslide Gjermo located in the middle of catchment area, using the software RocPlane, estimation of eroded volume of landslide with a risk of a damming of the river and determination of possible consequences due to these events. The presented methodology also includes elements of detecting unstable zones applying Differential Interferometry Synthetic Aperture Radar technology. Several consequences with the landslide probability classes are defined, and they are combined as pairs of values in a risk matrix. Results are presented in a form of susceptibility maps for several scenarios (in relation to the values of the geotechnical parameters and the saturation degree of the ground) and the final landslide risk map. The obtained susceptibility maps show that shallow landslides models depend a lot on the saturation degree, but in the analyzed cases, it is evident that the area of Gjermo village landslide is in the zones where the safety factor F<1. From the prepared landslide risk map it is evident that the area of Gjermo village is at the highest risk. The surrounding area of the village, where some houses can be affected together with local infrastructure and the zone around the Hydro Power Plant - HPP3 are at medium risk, and the rest of the catchment area is at low risk because there is no population or infrastructure to be affected by possible sliding. The prepared maps can be used in the design of protection measures necessary to reduce the possible consequences.