Abstract
Vertical Electrical Soundings (VES) provide fast and economical measurements used in geophysical exploration. VES were carried out in El Sauz-Encinillas (ESE) aquifer, in northern Mexico, to determine apparent resistivity and geoelectrical units’ thickness. Despite it being one of the three main aquifers feeding Chihuahua city, a lack of available geophysical data prevails in its northern portion. The main goal of this study was the determination of the geoelectrical units in the subsurface stratigraphy via electrical-resistivity soundings. The ESE’ aquifer is located within alluvial Quaternary sediments, with varying granulometry and reaching from a few meters to more than 600 meters of thickness at the center of the valley. Forty-five vertical electrical resistivity soundings (Schlumberger array, maximum AB/2 distance of 500 m) were performed throughout ESE aquifer’s northern portion. Field data were analyzed using software. Results illustrate a wide variability in resistivity values throughout the study area. Five geoelectrical units were identified: 1) a hardpan topsoil, with resistivity values ranging from 200 - 800 Ω-m ; 2) an alluvial material mixture (sand/silt) with resistivity values ranging from 25 to 100 Ω-m; 3) playa lake-type material (clay/evaporites mixture) with resistivity values ranging from 0.2 to 15 Ω-m; 4) a gravel/sand mixture with resistivity values from 100 to 300 Ω-m; and 5) a partly fractured rock or conglomeratic material with resistivity values ranging from 400 to 3500 Ω-m. The electrical resistivity data, therefore gives reasonably accurate results that can be used to understand the subsurface stratigraphy and basement configuration in groundwater exploration.
Highlights
Five geoelectrical units were identified: 1) a hardpan topsoil, with resistivity values ranging from 200 - 800 Ω-m ; 2) an alluvial material mixture with resistivity values ranging from 25 to 100 Ω-m; 3) playa lake-type material with resistivity values ranging from 0.2 to 15 Ω-m; 4) a gravel/sand mixture with resistivity values from 100 to 300 Ω-m; and 5) a partly fractured rock or conglomeratic material with resistivity values ranging from 400 to 3500 Ω-m
Vertical Electrical Soundings (VES) provide fast and economical measurements used in geophysical exploration and groundwater studies
The shallow sub-surface stratigraphy was delineated through investigations conducted via electrical resistivity surveys
Summary
Vertical Electrical Soundings (VES) provide fast and economical measurements used in geophysical exploration and groundwater studies. Rapid expansion of urbanized zones within arid climate areas, plus growing populations and an ever-increasing need for water has led to a growing consumption and an overexploitation of water resources In desertic areas such as Chihuahua, in northern Mexico, surficial water sources are limited and generally with poor quality, groundwater resources are the most important source of water for both human consumption and economic activities. A spike in groundwater extraction from water wells within the area has led to degradation of water quality, rapid drawdowns, and change of groundwaters’ flow direction [1] Previous work in this aquifer was related to geology [2] [3] [4] [5], geophysics [6] [7] [8] [9] [10], hydrogeology [1] [11]-[16] and groundwater flow models [17] [18] [19]. The fine-grained sediments of the Laguna, product of the weathering of igneous rocks in surrounding ranges, hinder surface water’s infiltration, favoring evaporitic deposits and providing a chemical signature to northern ESE’s groundwater [13] [15] [16]
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