Evaluation of groundwater recharge estimation methods in a watershed in the Brazilian Savannah

The Brazilian Savannah Biome is strategic for Brazilian agriculture and for maintaining Brazil's hydrological balance, contributing to river flows from eight of the twelve Brazilian hydrographic regions. In recent years, there has been a continuous growth of irrigated agriculture, the main activity that uses the water resource, and the emergence of conflicts over water use. Thus, to improve water resource management in the Brazilian Savannah, it is important to better understand groundwater recharge rates to determine the magnitude of the sustainable groundwater resource in the region. The study aimed to evaluate groundwater recharge estimation methods in a watershed located in the Brazilian Savannah region. For this, recharge rates were calculated for the period from October 2009 to September 2011 using the methods of baseflow separation, water table fluctuation, and a sequential water balance (BALSEQ). The recharge rates estimated by the baseflow separation, and water table fluctuation methods were, respectively, 23.7% and 26.6% of the total rainfall of 1753.8 mm in the watershed. Using the BALSEQ water balance method, the potential recharge for the period was estimated to be 31.5% of annual average precipitation. The recharge estimates calculated by the methods were consistent with those observed in other agricultural watersheds in the Brazilian Savannah Biome. Also, the evaluated methods can be used as a tool by water resource managers for the rational use of groundwater.