Hazard Assessment of Debris-Flow Prone Watersheds in Cubatão, São Paulo State, Brazil

Abstract In Brazil, research related to the occurrence and prevention of debris flows is incipient when compared to the extent of the impacts caused by the phenomena. There is a need for more studies that consider their susceptibility and hazard, especially in areas that are environmentally and socioeconomically vulnerable. This study aims at assessing debris-flow hazard in the Rio das Pedras watershed, in Cubatão (São Paulo State, Brazil), based on a set of different physiographic parameters (geomorphological, morphometric, geological) and the application of empirical models. The hazard assessment was based on: (i) the evaluation of the history of events in the region; (ii) the identification of the geomorphic controlling factors; (iii) the estimation of the magnitude of a potential event and, (iv) the identification of the elements at hazard. The results show that a debris-flow event in Rio das Pedras would more severely impact the Anchieta Highway (SP-150), the gas pipeline GASAN, the oil pipeline OSSP, and the districts Pinhal do Miranda and Cota 95. The results showed the relevance of geomorphological and geological parameters in estimating the magnitude of debris runoff for defining the danger in watersheds susceptible to the occurrence of debris flows.