Overexploitation assessment in an urban karst aquifer: The case of Sete Lagoas (MG), Brazil

Abstract

Overexploitation of groundwater in urban karst aquifers can lead to negative consequences such as land subsidence, depletion of springs and lakes, and water pollution. It can also have indirect effects such as environmental, socio-economic, and political instability. In the municipality of Sete Lagoas, Brazil, the long-term effects of extensive groundwater extraction have been observed and studied over the years. This paper analyzes the response of the karst aquifer to urban, industrial, and climatological changes that may have contributed to changes in the aquifer over the last four decades. The results show that groundwater extraction has exceeded the average aquifer recharge since the year 2000. From the 1980s, the number of wells has steadily increased due to unplanned urban development, resulting in higher demand for groundwater. In the 2010s, pumping from tubular wells (7.39 × 107 m3/yr) exceeded the maximum recharge capacity of the aquifer (7.33 × 107 m3/yr). These wells are mainly concentrated in two areas: the central urban zone and the industrial sector. As a result, kilometer-long cones of depression have formed, changing the aquifer from confined to unconfined within these regions. According to the census data, about 67% of the wells remain unidentified. The average annual recharge to the aquifer is estimated to be 5.68 × 107 m3/yr, which accounts for 12% of the average annual rainfall in the region. Climatological trends indicate an incipient decrease in precipitation and an increase in temperature, suggesting a potential decrease in future aquifer recharge. In addition, only 17% of the area has high infiltration rates ranging from 35% to 75%. The current situation in Sete Lagoas is one of overexploitation of groundwater resources, which could be mitigated by localized reduction of groundwater consumption and implementation of effective management strategies to increase aquifer recharge.