HYDRODYNAMICS AND INTRINSIC VULNERABILITY OF THE ÉDEN CAVE KARST SYSTEM, PAINS - MG

Abstract

Karst aquifers are naturally more vulnerable to contamination than other types of aquifer. They are made up of complex conduits and cave systems networks, where surface and meteoric water can be rapidly transferred to the phreatic zone where underground flow can be turbulent. These heterogeneous and anisotropic characteristics makes it difficult to determine the karst network and flow directions, being necessary to apply specific karst hydrogeology methods. This article aims to map the intrinsic vulnerability zones of the Éden Cave karst system (the largest cave in the region) in the São Miguel river watershed, MG, as well as understanding its spatial and seasonal variations in flow parameters (mean velocity and longitudinal dispersion), and its recharge and discharge mechanisms. Therefore, the EPIK method was adapted to map the system’s vulnerability zones, associated with tracer tests (sodium fluorescein)
during the dry and rainy seasons, and the breakthrough tracer curves were analyzed to obtain the flow parameters. The results show that the flow is controlled by folds forming karst windows and by subvertical fractures/faults in NW-SE and N-S directions. Recharge proved to be diffuse in places with thicker soils and concentrated in dolines, sinkholes and rock masses; the discharge zones are close to the São Miguel riverbanks, which is the local base level. The breakthrough tracer curves showed that this system is sensitive to seasonal variations and pointed to the existence of heterogeneities, which control the variation of the flow parameters. The greatest vulnerability zones are related to areas without protective cover with concentrated recharge (autogenic) and the highest flow velocities. The combination of different techniques proved to be effective in understanding the hydrodynamic behavior and its relationship with the vulnerability of the karst system.