Application of vertical electrical sounding resistivity technique to explore groundwater in the Errachidia basin, Morocco

Abstract

The resistivity technique involving Vertical Electrical Sounding (VES) was carried out North of Ain Al Atti area, in Zaouia Jdida locality, with the aim of delineating zones not contaminated by the extension of the salinity and determining the potentiality of the existing aquifers. The measurements of apparent resistivity were collected using MolisanaApparecchiatureElettroniche (MAE) advanced geophysics instruments and were taken in twenty two VES points, along four profiles oriented N-S. The VES profiles were implanted using the Schlumberger configuration. VES Interpretation results shows that the potential aquifer horizon consists of the infracenomanian sand. The isopach map shows that the thickness of this geological formation varies between 20 m and 170 m. The sand layer is more thick (>80 m) along the profiles P3 and P4, with a maximum of about 170 m at 2P4 and 3P4 VES points. The isohypse map indicates that the sand formation is shallow (<10 m) in the East, and the depth of the roof of the infracenomanian sand increases gradually towards the West of the prospect area (>30 m). The transverse resistance (Tr) map shows that the identified aquifer has high values of Tr (Tr > 50000 Ω m2) in the western part, corresponding to zones with relatively high thickness and may have high transmissivity. The longitudinal conductance anomaly (Sl > 0.6 Ω-1) indicates that the area delimited by 1P2, 4P2, 1P4 and 3P4 VES points may have an important underground hydraulic potential. The interpretation of the acquired data also shows the presence of small depressions that could be implicated in the storage of the infracenomanian groundwater. Furthermore, the resistivity results reveal the presence of electrical discontinuities interpreted as faults and fracture zones. These could be the preferential axes of the groundwater circulation.