Effects of Drainage Network on the Identification of Landslide-Susceptible Areas Using the TRIGRS Model

Gravitational mass movements are recurrent events in Brazil, usually triggered by intense rainfall. When such rainfall events occur in urban areas, particularly on slopes, they often result in disasters, causing loss of human lives, social impacts, and economic damage. Thus, mapping and monitoring landslide susceptible areas are extremely important, as well as the implementation of a system capable of predicting their occurrence in advance. In this context, this study aims to assess the efficiency of the TRIGRS numerical model as a component of a prediction system for landslides on urban slopes. As a first step, the influence of the drainage network, which is altered due to urbanization on slopes, will be analyzed in relation to the safety factor, moisture profile, and pore pressure. The drainage network was calculated using a digital terrain model derived from LIDAR data. The TRIGRS model was applied to a small watershed located in the municipality of Campos do Jordão, São Paulo, Brazil. During the 72 hours analyzed period, two heavy rainfall events stroke the area and landslides were registered. The registered landslides show the model efficiency on the identification of the most susceptible areas, because they happened in areas identified by TRIGRS as extremely susceptible to landslides. The combined geotechnical and geophysical methodology for soil characterization and the use of more realistic drainage network feeding the TRIGRS has shown to be useful urban planning and early warning systems. This study is part of Brazilian Council for Scientific and Technological Development (CNPq) Project coordinated by GEGEP/UFPE, with the participation of Cemaden, and in collaboration under development with the National Research Council of Italy (CNR). It aims to implement a methodological procedure.