Numerical Flow Model of Guarani Aquifer System (GAS) in Outcrop Region - Artigas (UY)/Quarai (BR)

Numerical models for groundwater flow is being used to aid the management of groundwater resources, given to managers tools to take right decisions in areas where the intense use of the groundwater has taken the depletion in groundwater levels or alteration of its natural quality. Guarani Aquifer System (GAS) represents in Quarai and Artigas, cities located in the border between Brazil and Uruguay, the main reservoir used for water supply, where groundwater superexploration has produced increase in drawndown water levels. Using the software Visual ModFlow 4.1® a numerical simulation of groundwater flow was achieved with the main purpose to reproduce the piezometric surface in steady state. The study area was discretized in 16284 cells in a single layer with 150 meters of thickness. In order to obtain a calibrated numerical model, recharge, hydraulic conductivity, height of water in the streams and the conductance of the stream bed, were chosen to calibrate the model. The results attempt by this simulation reproduces the piezometric surface observed currently, showing good correlation between calculated levels and observed ones, and the differentiation between the recharge which directly reaches the GAS in outcrop zones and which ones occurs in the zones where the aquifer is overlapped by the basalts.