Control of fracture networks on a coastal karstic aquifer: a case study from northeastern Yucatán Peninsula (Mexico)

Abstract

The Yucatan Peninsula karst aquifer in southeastern Mexico is important because it is the only source of freshwater supply in the region. Along the eastern coast, the aquifer behaves as a shallow unconfined aquifer, and one of its main characteristics is the development of a complex network of karstic conduits. Electrical resistivity tomography (ERT) is a geophysical technique that provides reliable information on aquifer properties that can be applied to karst. With this in mind, ERT surveys (with dipole-dipole and Wenner arrays) together with vertical profiles of groundwater electrical conductivity were obtained in the northeast of Yucatan Peninsula in the Akumal zone. The objective was to evaluate the characteristic structure of the unsaturated and saturated areas, and to determine the importance of factors at a local level that affect the thickness of the freshwater lens, as well as groundwater flow directions near the coast. The results of the ERT sections show a thin vadose zone with resistivity values greater than 1,052 Ωm and a saturated zone with resistivity values that vary from 1 to 1,052 Ωm, and show the presence of dissolution conduits and fracture zones that are affecting the freshwater lens of the aquifer. In addition, water-table measurements show the role of fracture networks in the groundwater flow. The overall results indicate conditions for a possible microbasin in the Akumal zone, highlighting the importance of local fractures, which could work as groundwater divides along the eastern coast of the Yucatan Peninsula.