O parâmetro resistência elétrica transversal e sua aplicabilidade ao estudo do Aquífero Barreiras no litoral sul do RN - análise qualitativa e composição em uma cartografia exploratória de transmissividade hidráulica

Abstract

The cities on the east coast of Rio Grande do Norte rely on the Barreiras Aquifer for about 80% of their water supply, which has a hydraulic character that is predominantly unconfined. In this context and considering the aforementioned water source, this research targeted two distinct areas: the first encompasses the Catu River basin in RN, and the second is located on the left bank of the Boa Cica Stream, in the municipality of Nísia Floresta-RN. Both areas are carved into the Cenozoic sequences of the Barreiras Formation and its coverings. The objective was to identify subareas with greater hydrogeological potential using geoelectric data. The methodology was based on local transverse electrical resistance (RT) parameter studies and its direct correlation with hydraulic transmissivity. In the Catu River basin area, the northeastern and central regions showed RT values higher than 50,000 Ohm.m², which are associated with sectors of thickness and/or average resistivities of the saturated zone, indicating these subareas as the most promising in terms of hydrogeological potential. The greatest average thicknesses of the saturated zone are located in the northeastern and central portions, reaching 95 meters, while the highest values of average resistivities of the saturated zone are in the central and extreme northeastern parts of the area, reaching 950 Ω.m. However, linear regressions revealed that the average saturated thickness has a greater influence on the calculation of transverse electrical resistance, with a correlation factor of 0.70, while the average resistivity factor was 0.47. The RT results for the left bank area of the Boa Cica Stream showed the highest values in the southern and western portions, reaching 58,860 Ωm², associated with zones of greater thickness and/or average resistivity of the saturated zone. In this regard, and in contrast to the results obtained in the Catu River basin area, the analysis of the predominant factor in the RT calculation, carried out through linear regression, revealed a predominance of the average resistivity parameter of the saturated zone, associated with hydraulic conductivity, showing a correlation factor (R²) of 0.89. Additionally, considering the direct proportionality with RT and through an aquifer test for geoelectric calibration in this area, a preliminary map of hydraulic transmissivities (T) was developed. The results support this methodology as promising in identifying higher hydraulic transmissivities and, consequently, hydrogeological potential, especially in regions with limited well information.