Estudos das águas da bacia hidrográfica do rio Banabuiú no trecho entre Quixeramobim e Banabuiú - Ceará, Brasil

Abstract

The area of this hydrogeological study covers the Banabuiú Basin, in the stretch between Quixeramobim and Banabuiú, and is located on the banks of rivers Quixeramobim and Banabuiú. It is necessary for users and water managers to be aware of the qualitative and quantitative aspects of the water and the interaction between the rivers Quixeramobim and Banabuiú and the alluvial aquifers. For these reasons, we sought to deepen the knowledge about the hydrogeology of the alluvial deposits with respect to reserves, hydrodynamics and water quality. Methods included a data bank of wells, monitoring of changes in static levels, a planialtimetric survey, a geophysical survey by electric resistivity, measurements of physico-chemical and biological parameters, heavy metals, stable isotope analyses (18O and D) in rain, waters from wells, rivers Banabuiú and Quixeramobim, and Banabuiú dam. An estimation of reserves of alluvial aquifers was also made. In the treatment and interpretation of the data Piper and USSL diagrams were used as well as, Ato and Resist for interpretation of VES, program Surfer 8.0 for simulation of groundwater flow; potability standards of Portaria Nº. 2914/2011 of the Ministry of Health were used to judge water quality. Results indicate that the groundwater flow has in the same direction of rivers Quixeramobim and Banabuiú, ie eastward. The alluvial aquifer has an average thickness of approximately 7.1 m. The recharge to the alluvium in the stretch between Quixeramobim and Banabuiú was of 6.09 x106 m3/year and permanent reserve is of approximately 34.8 x106 m3. The main problems for human consumption of the waters (surface and groundwater) are total coliforms, the element iron, high salinity, nitrate, manganese and aluminum; these present values higher than permitted by Portaria Nº 2914. Therefore, these waters can only be consumed after proper treatment. In irrigation, surface water and alluvium can be used without many problems; however, waters from the crystalline domain require a practice of controlled irrigation. The stable isotope local meteoric water line for the period studied showed a slope very similar to the GMWL. The alluvial aquifers receive recharge from rivers Quixeramobim and Banabuiú. Wells in the crystalline bedrock receive recharge by rainwater. The waters of the alluvial aquifer wells suggest that they suffered evaporation while recharging. Finally, there is a slight stratification in Banabuiú dam (thermal and chemical) in the rainy season that disappears in the dry season.