Monitoramento da flutuação dos níveis de água em aquíferos freáticos para avaliação do potencial de recarga em área de afloramento do Sistema Aquífero Guarani em Cacequi - RS

Abstract

This research aimed to estimate the recharge and groundwater water table fluctuation in areas with withdrawals of groundwater and surface water related to the variation of groundwater levels and rainfall events. The two areas of study was inserted within the Cacequi Municipality, which is located in the Rio Grande do Sul state, southwestern Brazil, in the Guarani Aquifer System outcrops zone in the Paraná Sedimentary Basin. These two areas were selected because they have great applicability to the subject (water table fluctuation and recharge). The study was conducted in different areas of water withdrawals (surface and groundwater). It was installed a Monitoring Network, composed of three monitoring wells. The period of analysis was from February 01/2011 to 21/2012. During this hydrological period, there were executed campaigns for collection of information stored and biweekly checks of the conditions of automated dataloggers and the accuracy of records. Was used the Water Table Fluctuation (WTF) method for estimating groundwater recharge in uncofined aquifer. WTF is based on the variation of groundwater water table fluctuation recorded in automatic 3 dataloggers and 1 barologger, installed in three wells and measurements from hour to hour. Were performed in laboratory physical analyzes of the soil/rock characteristics (particle size and porosity). Were determined the values of specific yield - Sy and the sum of the values of water table fluctuations for each curve extrapolated recession - Δh used by the WTF method. The effective recharge estimated in the area with surface withdrawals accounted for between 11.5% and 13.9% of precipitation (1,572 mm) occurred during the hydrological 386 days, the range of the water table fluctuation obtained in this area from 1.17 to 5.15 meters, while the effective recharge the estimate was estimated in the area with groundwater exploitation represents about 25% of the precipitation (778.1 mm) occurring during a period of 243 days, and the range of fluctuation of the water table was between 8.4 to 16.46 meters. The present results provide subsidies for the sustainable management of groundwater resources, and also illustrate the development of new research on the exploitation of groundwater in the uncofined aquifer outcrops zone.