Variação espaço-temporal da expansão urbana e da rede de drenagem da Bacia do Igarapé Grande na cidade de Boa Vista, Roraima

Abstract

This study objectified the evaluation of the variation space-weather of urban expansion and of the net drainage of the basin of the narrow river “Grande” as a preponderant factor for the significant advance in the alteration of the natural draining of the water, whose consequence is sufficiently drastic in relation to the preservation of the environment. To carry out this research they were required the site of the INPE, the images TM/LANDSAT-5 of the years of, 1985, 1990, 1995, 2000, 2004 and 2009. The analysi of the cited images resulted in the visual interpretation of the clippings of the images TM/LANDSAT-5, and the elaboration of the MDE (digital model of the water line) and of the method of classification of the images. After the manipulation of the data in the digital way, the results have been presented in thematic maps in the scale of 1:80.000 and 1:90.000 representing the total urban area, and 1:40.000 and 1:55.000, for the micro basin. The results had signaled for the speed up process of urban expansion and the inadequate use of the ground. The alterations in the basin of the narrow river “Grande” can be evaluated in two levels, first, because of the indirect influence and second, in virtue of the execution of direct alterations of the canals. The speed up process of expansion of the city of Boa Vista caused the following alterations: the withdrawal of the primitive vegetation and the water protection of the soil, covering up the area of natural springs and stopping the water drainage at head of the river, for the construction of housings and roads, construction of houses in the bed of the canals and constructing canals for pluvial drainage. One transformation of the morphology of the canal of the narrow river ”Grande” and “Paca” attributed to the flooding of low lands and prompted withdrawal of the bush, the dam construction in the APPs, the architecture of bridges and streets in the transversal section of the canals. Such modifications have affected the lakes in the areas, modifying the dimensions of some of them and extinguishing the others. The geometric measures of the canals have also been modified, regarding standards as (length, width and depth) have original deprived of characteristics, due to the interventions of creation, rectification and magnifying the draining net. Showing that the net of draining in the period of 1985 to 2010 culminated with the extinguishing of certain canals and the re-stabilization of others through canalization and significant reduction of the lakes compared to the year of 1985.