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Maria Giovanna Parizzi, Universidade Federal de Minas Gerais (Brazil)
Joana Maria Cajazeiro, Universidade Federal de Minas Gerais (Brazil)
Christiano Nogueira, Universidade Federal de Minas Gerais (Brazil)
Poliany Figueiredo, Universidade Federal de Minas Gerais (Brazil)
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This case study research was based on rainfall and soil cohesion measurements in the East and Northeast districts of Belo Horizonte City, Minas Gerais State, Brazil. During the rainfall season from Nov/2006 until Mar/2007, pluviographers and tensiometers provided daily precipitation data together with soil matric potential values. Landslide occurrences of the same time period were given by the city's Urbanization Department-URBEL. Very heavy rainstorm occurred from November 27th until December 1st, and a total of 252 mass movements were detected in the City in one single day, the 30th of November. The East district counted 132 occurrences while the Northeast counted 41 occurrences during the whole rainy season considered. Measured data shows that precipitation was above the historical averages. The amount of precipitation in November was 419,4 mm, which 309,6 mm was concentrated on its four last days. It seemed that such a particular intense rainfall played a major role in triggering mass movements than a steady-state one. The geological and geomorphological differences between the two areas also explain the greater landslide susceptibility of the East district. The soil matric potential values were greater for the Northeast district granite-gneiss regolith soil than for the weathered shale and schist of the East district, where the slopes were also steeper. Besides the natural landslides triggers both districts are occupied by socially disadvantaged inhabitants whose inadequate constructions increases the landslide risks, causing undesirable economic and human losses. The Urbanization Department of Belo Horizonte (URBEL) is responsible for the urban planning and management of 188 favelas (poor, densely and inadequate populated urban areas) where almost 363.000 inhabitants live under low to high levels of landslide risks. The measurements, provided by the pluviographers and tensiometers, have revealed a possible correlation between rain intensity and soil cohesion, which should be considered a helpful strategy in improving the chances of landslide risks prevention during the rainy season. The Structural Program of Risk Areas (PEAR), developed by URBEL, is now investing in the acquisition of such instruments in order to refine the allocation of funds for risk management in all the nine city districts. Despite its warning system program, its action includes the adequation of the constructions and/or the terrain when possible, or the relocation of the inhabitants when necessary.
Key-words: rainfall intensity, landslide susceptibility, irregular urban occupation, risk management
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