Hydrologic Simulation for Water Balance Improvement in an Outcrop Area of the Guarani Aquifer System

Abstract

The Guarani Aquifer System (GAS) is the largest transboundary aquifer system in South America. One great challenge of managing the GAS is determining the effect of its exploitation for urban, industrial and agricultural use. The fully distributed, process-oriented hydrological model J2000 implemented in the Jena Adaptable Modelling System (JAMS) was used in this study to simulate the water balance in the Ribeirao da Onca (Onca Creek) watershed, because this is an outcrop zone of the Guarani Aquifer System (GAS). The J2000 model proved to be a flexible and easy-to-use tool. The constructed model was effective in predicting the hydrological response of the basin, showing a Nash-Sutcliffe coefficient of 0.76 and 0.81 during periods of model calibration and validation, respectively. The model adequately predicted the discharge volume, presenting percent biases of −0.66 and −2.80 % and root mean square error of 0.14 and 0.18 m3 s−1 for the two periods. The historical reconstruction of the flow series demonstrated that baseflow represents 86–98 % of the total annual discharge and 24–30 % of the total rainfall volume in the Ribeirao da Onca watershed. These estimates can be used to estimate the groundwater recharge rate, in order to establish quantitative targets to prevent overexploitation in the GAS water management. Additionally, the model can be used for further studies to determine the effects of land use and climate change on the hydrologic cycle of the basin.