Dynamics of mass movements in an urban basin: a case study in the Fradinhos drainage Basin, Vitória, Espírito Santo, Brazil

Landslides are a widespread problem in Brazil due to the heavy rainfall typical of hot and humid tropical environments. In urban areas, landslides can be catastrophic with significant economic and social losses, making it crucial to understand the local dynamics as a preventive measure. Therefore, the aim is to identify the spatial distribution of areas susceptible to shallow translational landslides in the Fradinhos Hydrographic Basin (FHB), located in the municipality of Vitória, Espírito Santo State (ES, Brazil), since a significant number of such morphodynamical processes are recorded in this basin. Another aspect that confirms the choice of this area is the fact that it has undergone a process of urban expansion, which has altered the geohydrogeomorphological conditions of the slopes. For the modelling, the Transient Rainfall Infiltration and Grid-based Regional Slope Stability (TRIGRS) model was selected and applied, analyzed in conjunction with geotechnical and hydrological data obtained in the field. The areas susceptible to translational landslides were modelled for a rainfall episode of 744 mm in 24 days (the highest monthly accumulation in the entire 60-year historical series (1961 to 2021), which occurred between 6 and 26 December 2013), which is considered an extreme climatic episode for the capital of Espírito Santo. The results show that 31% of the basin is unstable and another 69% is stable. According to the Municipal Master Plan, 86% of the territory is in an Environmental Protection Zone, 7% in a Special Zone of Social Interest and 6% in a Zone of Restricted Occupation. It should be emphasized that the preservation of the Environmental Protection Zone is of fundamental importance, as it forms a protective belt against the outbreak of shallow translational slides. It was also expected that the unstable areas (FS