Abstracto
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Authors
Mojica, Alexis; Castrellon, Maria; Ruiz, Alberto; Fabrega, Jose; Saavedra, Sidney; Salceda, Miguel; Serrano, Eny; Esquivel, Alexander
Abstrac
In recent years climate change has diminished access to water during the dry season in the south-central area of the Isthmus of Panama. Improving access to water during the dry season implies relying more heavily on groundwater sources. Nevertheless, this region of Panama is geologically and tectonically complex, and its fractured rock aquifers have not been fully characterized. Therefore, understanding the spatial distribution of the fractured geological bodies crucial for the development of groundwater resources and aquifer management policies for this region of Panama. The Estibana sub-catchment, located in south-central Panama was the selected study site. In order to identify fractured bodies, the 2D electrical resistivity imaging technique was applied along two profiles of 235 m long. Pseudo-sections of apparent electrical resistivity values were obtained with a Wenner-Schlumberger array. A 2D electrical inversion was applied to these two data sets using BERT (Boundless Electrical Resistivity Tomography) which is based on a smoothness-constrained Gauss-Newton method. The quality of the field data was acceptable (<1%) and low values of error-weighted chi-square fit (0.64 and 1.38) were obtained. Additionally, a forward simulation based on the subsurface discretization by numerical methods was performed. From the distribution of true ground resistivity sections superficial horizons with low and intermediate values of calculated resistivities (4 - 22.8 ohm-m) were identified. This range of resistivities is usually associated with sedimentary rocks such as shales and sandstones, typical of the Macaracas Valley. Also, a strong electrical anomaly (54.45 - 130 ohm-m) was found at 10 to 20 meters below ground surface, which strongly indicates the presence of a basaltic body at depth. It was also possible to identify fracture zones related to a regional fault of northwest orientation corresponding to a nearby riverbed. The direct simulation showed that the model response (synthetic field data) was in agreement with the measured field data. These results will help understand how fractures affect surface water groundwater interactions in this particular sub-catchment and thus will inform the development of a groundwater numerical model for this area of Panama.