Estimativa de recarga do sistema aquífero guarani por meio da aplicação do método da variação da superfície livre na bacia do Rio Ibicuí-RS

The estimation of groundwater recharge is determinant for the sustainable groundwater management. The recharge can be estimated using different methods according to the characteristics of the studied area, the spatial and temporal scales and data availability. The goal is to estimate the recharge of unconfined aquifer units that belong to the Guarani Aquifer System, located in the Ibicui River basin, based on the application of the Water-Table Fluctuation (WTF) method. The water level data were obtained from five monitoring wells of the RIMAS project operated by the CPRM/Brazilian Geological Service. The method was applied to the monthly average of the water level to each monitoring well, in periods between 24 and 39 months. The monthly recharge estimations were about 417,0 mm to 730,7 mm, and the values of precipitation that correspond to recharge varied between 11% and 18%, with an average of 13,82%. It was observed that the highest values occurred in the northwest region of the basin, while the lowest were found in the southern region. The method delivered good results when compared to other assessments that were carried out in the same region.