Calibration and validation of the stability index of hillslopes with an inventory of natural landslides in the Rio da Onça basin in the mountain range of Cubatão (São Paulo State).

Abstract

The occurrence of shallow translational landslides in the São Paulo coast is integrant part of the natural evolution of the hill slopes, and it is intensifies under conditions of tropical climate in a morphology of mountain about 700 m high. Under intense precipitations, without the direct interference of the man, the landslides may occur as an isolated or generalized form, as the hundred of landslides registered in the summer of 1985 January, when the rainfall intensity in 24 hours was 210 mm. Using an inventory of landslides scars obtained on aerial photos from 1985August, it was defined as objective to calibrate and to validate a map of stability index using the model of infinite slope stability, available in the program SINMAP, for the mountain range of Cubatão, scale 1:10.000. The model was applied considering both constant parameters for all area and changeable parameters in function of the lithological boundaries. The results demonstrated that more than 79% of the scars were within the lower and upper threshold of instability in the case of constant parameters, and more than 95% of the scars in the case of changeable parameters applying the same limits. Keywords: Stability index, landslides, Serra do Mar.