Abstract
Mass movements in Brazil are common phenomena, especially during strong rainfall events that occur frequently in the summer season. These phenomena cause losses of lives and serious damage to roads, bridges, and properties. Moreover, the illegal occupation by slums on the slopes around the cities intensifies the effect of the mass movement. This study aimed to develop a methodology that combines models of shallow landslides and debris-flows in order to create a map with landslides initiation and debris-flows volume and runout distance. The study area comprised of two catchments in Rio de Janeiro city: Quitite and Papagaio that drained side by side the west flank of the Maciço da Tijuca, with an area of 5 km2. The method included the following steps: (a) location of the susceptible areas to landslides using SHALSTAB model; (b) determination of rheological parameters of debris-flow from the back-analysis technique; and (c) combination of SHALSTAB and FLO-2D models to delineate the areas more susceptible to mass movements. These scenarios were compared with the landslide and debris-flow event of February 1996. Many FLO-2D simulations were exhaustively made to estimate the rheological parameters from the back-analysis technique. Those rheological coefficients of single simulation were back-calculated by adjusting with area and depth of the debris-flow obtained from field data. The initial material volume in the FLO-2D simulations was estimated from SHALSTAB model. The combination of these two mathematical models, SHALSTAB and FLO-2D, was able to predict both landslides and debris-flow events. Such procedures can reduce the casualties and property damage, delineating hazard areas, to estimate hazard intensities for input into risk studies providing information for public policy and planning.
Highlights
Natural disasters constitute one of the largest socio-economic problems worldwide
A combination of SHALSTAB and FLO-2D models is used to delineate the areas where shallow landslides and debris-flows occurred in February 1996
The SHALSTAB map shows seven classes that vary from stable to unstable (Figure 6(a))
Summary
Natural disasters constitute one of the largest socio-economic problems worldwide. Among these, earthquakes, floods and mass movements are the most striking events. Nations [1], mass movements cause major financial damage and death. In cities, they may have catastrophic effects due to the various anthropogenic changes imposed on the natural landscape [2,3]. Weather conditions and geomorphological characteristics of the Brazilian coast facilitate the occurrence of mass movements. Apart from these natural conditions, anthropogenic activity along spillways triggers numerous mass movement events. The combination of shallow landslides with debris-flows caused catastrophic events in Rio de Janeiro, after the 1960’s when the low-income communities began occupying the steep slopes around the cities
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