Aplicação de dados orbitais no estudo da variação no volume de água nos açudes Pilões e São Gonçalo na região semiárida da Paraíba, Brasil.

Abstract

The present dissertation describes the study of the influence of the precipitation on water content flowing into the basins of Pilões and São Gonçalo dams, in the West region of the State of Paraiba - Brazil, using TM/LANDSAT-5 multitemporal image analysis in 1983 (drought year), 1985 (intensive precipitation year) and 1990 (normal precipitation year), as well as the hydrologic simulation model Tank-Model. The drainage basins of Pilões and São Gonçalo dams present the same order channel networks and similar hydrologic physical features, except river frequency, approximately doubled in the second relative to the first. The drainage pattern of the first basin is subdendhtic, whereas the second presents a dendritic drainage pattern. Geologically speaking, the drainage basin of Piioes dam is almost totally in the sedimentary rocks of Rio do Peixe basin, while the second basin is totally in a crystalline basement. The most significant results of this study in those basins are: 50% of the dams are localized in Bruno Not Calcicos soils, an excellent choice for dam, whereas 14% are built in Vertissolos areas, not recommended for this purpose due their cracks and fissures; aquatic vegetation is used to reduce the evaporation of stored water; between 1983 and 1990, seven dams with a water surface down or equal to 4.0 ha were built in the drainage basin of São Gonçalo dam, while the other basin lost three dams in the same period (nineteen in 1983 against sixteen in 1990); the increase of dams in the basin of São Gonçalo had not implied an intensive increase on the soil use of the region. Nevertheless the soil use of the basin of Pilões dam had an increase of 8,3%. According to the application of Tank-Model to the set of 1983 and 1990 monthly data, zero surface runoffs were obtained for the drainage basin of Pilões dam, while for the basin of São Gonçalo dam surface runoffs of the order of 14.7 (1983) and 50.3 mm (1990) were computed. Regarding to 1985, annual surface runnoffs of 586.7 e 473.7mm were generated by the model for the basins of Pilões and São Gonçalo dams, respectively. The surface runoffs analysis obtained by Tank-Model for 1985, taking account to the free water contents flowing into the basins - the water content flowed off into the basins without the interception of the dams of the upper side of the storage dams studied, these were sufficient to fill those dams. This imply the inadequacy of analysis of the influence of small dams in an intensive rainfall year, because an unreal information would be produced.

Regarding to 1983 and 1990, the runoff absence or almost absence in those basins ma'de impracticable the estimation of the influence of the dams of the upper side of the' storage dams considered in this study on the water content of São Gonçalo and Pilões dams.