Geomorphic analyses of two recent debris flows in Brazil

摘要

Debris flows are one of the main geomorphic processes resulting in economic and social losses in Brazil. Due to the recurrence of these events and the damage they can cause, it is necessary to better characterize the process to mitigate new occurrences and prevent casualties. On March 11, 2011, extreme rainfall contributed to triggering debris flows and shallow landslides in the Tingidor watershed (TW), causing three deaths, destroying houses, and partially destroying the main road to the state capital. Similarly, on January 13, 2014, rainfall-induced shallow landslides triggered debris flows in the Guarda-ma similar to o watershed (GW), causing 25 deaths and destroying infrastructure. Both areas are located in the Serra do Mar, a mountain range that extends for 1500 km along the south and southeast coasts of Brazil. The main goal of this work was to investigate and compare the main triggering factors and geomorphic characteristics of these two recent events. To achieve this goal, a landslide inventory was compiled, and the main debris-flow features were mapped in detail. Flow discharges, velocities and volumes were also estimated. Despite having an initial source volume more than 30 times smaller, the GW event had a total volume of approximately 237,700 m3, compared with 196,800 m3 in the TW event. Along with differences related to runout length and topography in both areas, the results demonstrate that entrainment is an important characteristic of debris flows in the two recent occurrences evaluated in Brazil.