Modelagem numérica do fluxo subterrâneo no perímetro urbano do município de Alegrete - RS

Abstract

In the city of Alegrete, the water supply is carried out using a surface water body (Rio Ibirapuitã) and groundwater (17 wells). The wells implanted in the region extract water from the Serra Geral and Guarani aquifer systems. This region suffers from scarcity situations and belongs to the Ibicui river basin in which the water balance situation is very critical, but still having the potential to exploit groundwater. In this way, actions and tools that measure or that can provide a greater understanding of the groundwater flow are extremely important in the management of groundwater resources. The objective of this work is to understand the dynamics of the underground flow in the urban perimeter of the city of Alegrete, in the state of Rio Grande do Sul, using numerical modeling as the main tool. The code used to perform the numerical modeling was MODFLOW-2005. This tool was able to simulate the three-dimensional flow of water in the underground medium in the steady state, using the governing equation of the underground flow as a starting point. The application of this tool included the construction of a database and a conceptual model. The conceptual model built for the study area includes two aquifer systems: Serra Geral and Guarani, with recharge rates of 1.3% and 8.1% for the Serra Geral and Guarani aquifer systems, respectively. The hydraulic conductivities were described for the horizontal and vertical axis having a minimum value of 1.16E-6m/s and a maximum of 3.12E-5m/s. In this region, 27 wells already installed were considered, with active pumping. The numerical model obtained hydraulic load values ranging from 78m to 176m. The mass balance showed that the river-aquifer interaction exerts a great influence on the hydraulic heads and volume of water contained in the model. The sensitivity analysis showed that the contours used as lateral limits of the study area are highly sensitive to hydraulic conductivity values. In this way, the recommendations are aimed at reducing the uncertainties of the lateral contours and the deeper investigation of the influence of the river-aquifer interaction.