The present work is part of a greater research project aiming at creating knowledge-base for the future managerial plans dedicated to the protection of caves heritage in the Correntes Basin (3904 km 2) located in the central Brazil. Here, a GIS-based relief compartment mapping of the area is done using satellite images, geological map and cave location map as input data layers. As a result four geomorphological domains were identified as i) lowlands (282 km 2) with a base-level in silicates and carbonates, ii) the karst terrains (994 km 2) which were developed in carbonates trapped by siltstone lenses iii) the talus (1483 km 2) having colluvial and alluvial units deposited by the Urucuia escarpment retreat and iv) the highlands (1143.7 km 2) developed over the sandstone of the Urucuia Group. The intersection of landforms and geological maps resulted in two abrupt contacts, the first between lowland and karst terrains, and second between the talus and highlands which formed canyon and escarpment, respectively. Two types of the cave systems are proposed in the region as superior/vadose that collect floods from hillslopes and deep epigene fluvio-karst.

The use of geophysical characterization of karst systems can provide an economical and non-invasive alternative for extracting information about cavities, sinkholes, pathways for water infiltration as well as the degree of karstification of underlying carbonate rocks. In the present study, three geophysical techniques, namely, Ground Penetrating Radar (GPR), Electrical Resistivity Tomography (ERT) and Very Low Frequency Electromagnetic (VLFEM) were applied at three different and appropriate locations in fluvial karst of a listed environmentally sensitive area of the Rio Vermelho, Mambaí, Goiás, Brazil. In the data acquisition phase, the GPR, direct-current (DC) resistivity and VLFEM profiles were obtained at three different locations in the area. Data were analyzed using commonly adopted processing workflows. Different radar typologies have been assigned to soil and rock typse. The GPR results showed a well-defined lithology of the site based on the amplitude of the signal. On the other hand, the inverted resistivity cross-sections showed a three-layered stratigraphy, pathways of water infiltration and the weathered structures in carbonate (Bambui group). The interpretation of VLFEM as contours of current density resulted from Fraser and Karous-Hjelt filters, indicate the presence of conductive structures (high apparent current density) that may be linked with the weathered carbonate and other conductive and resistive anomalies may be associated with the water-filled and dry cavities (cave). The results encourage the integrated application of geophysical techniques as the reconnaissance for further detailed characterization of the karst areas.

Unplanned urban growth exerts significant stresses on the underlying aquifers in terms of increasing the groundwater extraction and reducing the surface area for aquifer recharge. This situation has led to a more difficult process in the search for new locations of productive tubular wells, particularly in the Federal District of Brazil. In this region, the groundwater extraction is challenged by fractured aquifers with difficult identification of hydraulic tarps and significant uncertainty in the estimation of recharge potential. The aim of the present study is to optimize the demarcation of new locations of tubular wells by conducting geophysical investigations. In the first stage, based on the information of the physical environment and data from the existing wells, the total exploitable amount of groundwater was calculated. Then Electrical Resistivity Tomography (ERT) was carried out along specific sites, which were selected based on the surficial characteristics. The resistivity values obtained from the dipole-dipole array were inverted and the resultant conducting zones (weathered rocks and fractures) were delineated, which represent possible hydraulic traps where groundwater may exist. Based on the results, the suitability of the selected sites for deep tubular wells installation was prioritized on a linear scale varying from 1 to 5, where 1 is the highest and 5 is the least suitable. Based on this approach, eight new deep tubular well sites were proposed and classified. The study provides a promising framework for investigating groundwater in fractured aquifers.