Áreas de preservação permanente urbanas: mapeamento, diagnósticos, índices de qualidade ambiental e influência no escoamento superficial: estudo de caso: Bacia do Córrego das Lajes, Uberaba/MG

Abstract

Breaking itself on the affirmation that green is a necessity inside the cities and that green areas need to be to the reach of all citizens, this work has searched to diagnosis the situation of the green in the basin of the stream of Lajes, in the city of Uberaba MG. In this direction, it was tried to identify, to classify, to map and to quantify the free spaces, green areas and APP (Areas of Permanent Preservation), to characterize the space of the tree covering in these spaces, to diagnosis the degradation factors of three APP with possibility of transformation in AVDP (Green Areas of Public Domain) and to verify the influence of these APP in the attenuation of the peak outflows and volumes of runoff. The Geographic Information System SPRING provided necessary support for the interpretation of aerial photographs that enabled the systematization of data. The spaces were classified according to the methodology of Cavalheiro et al (1999). The results showed a green area/population ratio from 1.9 m2/person, free spaces/population ratio 2.9 m2/person and crop insurance/population ratio of 0.9 m2/person, while the average was: percentage of green areas 0.97%, percentage of free spaces, 1.45% and percentage of crop insurance 0.005%. The proposals of implantation of new green areas (or free spaces), assessed through prognostics, represented a substantial improvement on the current situation. In the diagnoses, beyond the photo-interpretation, were used on-site visits. The vegetation in places of study, is in its majority, impoverished by its biodiversity feature, with a free process of secondary succession. The vegetation non-feature or the exposed soil are responsible for the instability of embankments on the water bodies boundaries. It was concluded that measures to contain the erosive processes must be implemented quickly, in addition to the need for restoration of the vegetation in the areas of study and the withdrawal of other degrading factors. For the estimate of exceeding rain, the Number Method CN of Soil Conservaciontion Service was used (SCS). The hidrogramas of flood for the basins without reservoir of detention had been gotten by means of the direct application of Saint Bárbara Method, and in the basin with reservoir of detention, beyond the Saint Bárbara Method, were used the Pulz Method and the equations of Saint-Venant. The permeable areas contribute to damping of flow index and to reduce the volumes flowed off, especially when the soil is in normal conditions of humidity or dry. Under the conditions of wet soil, it was observed that this efficiency has been significantly reduced, exactly on the rainy months, when the instances of flooding are more frequent. Regarding the influence of APP in mitigation of peak flow rates and volumes, it was observed that only the APP with larger areas have showed efficiency, which highlights the importance of preserving other permeable areas, by limiting the rate of sealing in lots and deployment of new green areas, for the control of floods.