Numerical modeling as a support tool for groundwater permits in the state of Bahia, Brazil

Abstract

The western region of Bahia State is an important agricultural frontier in Brazil, generating a large increase in requests for groundwater usage in the last decades, mainly through large capacity water wells tapping the Urucuia Aquifer System (UAS). This study aims to develop a groundwater numerical model using the Visual MODFLOW software and the additional packages MODPATH and ZONEBUDGET to evaluate the effects of intensive groundwater pumping in eight possible scenarios of two areas (Central and Eastern) in the Alto Grande - São Desidério rivers sub-basin. Drawdown ranging from 4 to 20 m was observed in the different areas and scenarios. The analysis of the local flow path lines showed that the wells have an area of influence that captures part of the groundwater flow. The water balance indicated that the total volume pumped in the sub-basin did not reach 10% of the recharge in any scenario, considering the entire model domain. The high concentration of irrigation pumping wells in restricted areas resulted in a significant impact on the aquifer, reaching up to 84.6% of the local recharge, a value that is far above what is considered sustainable for the region. Results show that the eastern area is more susceptible to drawdown and changes in flow path lines by pumping. The applied method has proven to be useful to predict the effects of water abstraction on the aquifer before the implementation of projects, improving water resources management. Long-range forecasts and taking into account possible climate changes are also some of the advantages of the method, though it depends on reliable field hydrological and climate data.