Slopes instability and risks of mass movements. The example of the Vila Seca-Lamas area (south of Coimbra)

Abstract

Since 1993 we have been studying some important slope movements and their effects produced along the national road n° 342 (E.N. 342) between Condeixa and Miranda do Corvo (Coimbra-Portugal), at the section Vila Seca-Lamas. Our goals were to identify the principal factors that probably took part of those slope movements, and to look for possible hypothesis that could relate the influences of each one in the evolution of this kind of phenomena. The geological, geomorphological, hydrological and climatical aspects define the structure of this paper, but the emphasis goes straight to some aspects of the precipitation ("intensity" and "total accumulated" until the occurrence day). The human activity (also emphasized) is more and more important, as an element but specially as a factor that influences the "stability-instability" balance of the slope. In the present case the slope movements hazards have been classified in different zones according to the methodology of Plan ZERMOS (applied in France between 1974 and 1979). Such a simple document results in an important example of mapping slope movements hazards and risks, that can be applied to the local planning.