Urban expansion and geomorfological expansion in backwater of reservatories: comparative analisis of two drainage basins that are in the source of Guarapiranga, São Paulo / Expansão urbana e evolução geomorfológica em remansos de reservatórios: análise comparativa de duas bacias hidrográficas em guarapiranga, São Paulo

Juliana de Paula Silva

The environmental problems created by the accelerated urban growth in the last fifty years have brought severe consequences to the group of people living in big urban centers. For this reason many scientists, mainly in the field of Earth sciences, have searched the development of new techniques, methodologies and parameters to measure, recognize and attenuate the effects of these processes. The central objective of this work is to recognize and measure, through a geomorphological reading, the urban expansion as a kind of human intervention that is able to modify geomorphological processes and bring new morphodynamics to affected physical systems. Through this central objective the application and test of methodologies and parameters, proposed by the anthropogeomorphology for the context of a developing country located in the humid tropical climatic domain, was tried. According to RODRIGUES (1997a), by using the tools of the geomorphology it is possible to develop specific methodological proposals that insert the human action as a modifier agent of the systems of the Earth surface, as in TOY &HADLEY (1987); DOUGLAS (1983); TRICART (1977); TRICART &KILLIAN (1979); NIR (1983); DOUGLAS (1983); HART (1986); VERSTTAPEN (1983); GUPTA (1999a) and COLTRINARI (2001). In this research part of this methodological reference was applied, such as the Anthropogeomorphology NIR (1983), the Geomorphological Cartography RODRIGUES (1997a); LIMA (1990) and the Geoindicators COLTRINARI (2001); GUPTA (1999b) to evaluate quantitatively and qualitatively the geomorphological changes (shape, processes and materials) observed in the backwater of two drainage basins, one with almost all the area in an advanced stage of urbanization, and another with the greatest part of its area without human interference. The comparison between the results found in each drainage basin enabled the follow-up of the changes generated by the urbanization during the studied period. The areas chosen as object of study are the two drainage basins that are in the source of Guarapiranga dam, located in the south zone of Sao Paulo. This selection was made mainly because of the similar morphological characteristics of the drainage basins, and because of the distinguished dynamic of the process of urbanization in each of them. On the other hand, their importance in the metropolitan context provided a continuous generation of data along the entire 20th century. These data are available for consultation as: air photographs, maps, exploration studies, operation data, among other things. The spatial changes GREGORY (1992) occurred along the history of this dam and outskirts were analyzed through the cartographic production in detail scale (1: 5.000) for the years 1932, 1962, 1986, 1994 and 2000, in the selected backwaters for the evaluation of the morphodynamic processes generated by the urbanization after the construction of the dam in 1906. The quantitative character results found were: silting areas in the selected backwaters and evolution of soil use; the qualitative character results were: spatial changes in the morphology and in the fluvial channels generated by the urbanization, and analytical through the use and analysis of new methodologies which enhance the possibilities of the application of the physics geography

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