Modelagem numérica de fluxo das águas subterrâneas no Campus da Universidade Federal de Santa Maria, Santa Maria – RS

Abstract

Groundwater represents a resource of great importance for the social and economic development of the population. However, the increase in demand and the lack of knowledge of hydrogeological aspects ends up making the management of these water resources a great challenge. This management depends on how the flow phenomena is quantified and the relationships between the water inputs and outputs of the aquifer system under analysis are represented, with numerical modeling being one of the most frequently used approaches. Thus, the present research has as main objective to expand the knowledge about the hydrogeological behavior of the aquifer system of the campus of the Federal University of Santa Maria, Santa Maria - RS, through numerical modeling of flow in steady state. The free software QGIS Desktop, version 2.18.21, and the FREEWAT interface were used for the elaboration of the numerical flow model and the execution of the MODFLOW-2005 code, which uses the numerical method of finite differences to simulate flow. The development of numerical modeling was divided into the following steps: definition of purpose, construction of the conceptual model, formulation of the mathematical model and selection of the modeling code, elaboration of the numerical model, simulation and calibration of the model, and sensitivity analysis. The conceptual model was discretized in a domain of 11.55 km² with 4620 cells of 50 m². The calibration process was carried out using the “trial and error” method and statistical analysis of residual errors between hydraulic loads observed in the field and those simulated by the model. The model considered calibrated presented hydraulic conductivity values of 0.29, 1.0, 2.5 and 6.36 m/day in 4 different zones and precipitation recharge of 6x10- 5 and 0.0003 m/day in two zones (outcrop of Alemoa Members and Passo das Troopas). The outcrop zone of the Member Passos das Troops showed a recharge rate of 16.70% (299.48 mm/year), a value that is very close to the minimum rate found in other studies. The estimated underground water balance showed a participation of 69.55% of the recharge due to precipitation in the total water inlet and 44.08% of the pumping wells in the total water outlet of the system. The sensitivity analysis carried out with the isolated variation of the parameters showed that the recharge in the outcrop of the Passo das Tropas Member and the pumping wells are the most sensitive parameters of the calibrated model, which demonstrates the relevance and the care that new investigations need to have before these parameters.