Electrical resistivity method is a versatile and economical technique for groundwater prospecting in different geological settings due to wide spectrum of resistivity compared to other geophysical parameters. Exploration and exploitation of groundwater, a vital and precious resource, is a challenging task in hard rock, which exhibits inherent heterogeneity. In the present study, two-dimensional Electrical Resistivity Tomography (2D-ERT) technique using two different arrays, viz., pole-dipole and pole-pole, were deployed to look into high signal strength data in a tectonically disturbed hard rock ridge region for groundwater. Four selected sites were investigated. 2D subsurface resistivity tomography data were collected using Syscal Pro Switch-10 channel system and covered a 2 km long profile in a tough terrain. The hydrogeological interpretation based on resistivity models reveal the water horizons trap within the clayey sand and weathered/fractured quartzite formations. Aquifer resistivity lies between ∼3-35 and 100-200 Ωm. The results of the resistivity models decipher potential aquifer lying between 40 and 88 m depth, nevertheless, it corroborates with the static water level measurements in the area of study. The advantage of using pole-pole in conjunction with the pole-dipole array is well appreciated and proved worth which gives clear insight of the aquifer extent, variability and their dimension from shallow to deeper strata from the hydrogeological perspective in the present geological context.

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Characterization of the shear zone with pole-pole electrical resistivity tomography (ERT) was carried out to explore deep groundwater potential zone in a water scarce granitic area. As existing field conditions does not always allow to plant the remote electrodes at sufficiently far of distance, the effect of insufficient distance of remote electrodes on apparent resistivity measurement was studied and shown that the transverse pole-pole array affects less compared to the collinear pole-pole array. Correction factor have been computed for transverse pole-pole array for various positions of the remote electrodes. The above results helped in exploring deep aquifer site, where a 270 m deep well was drilled. Temporal hydro-chemical samples collected during the pumping indicated the hydraulic connectivity between the demarcated groundwater potential fractures. Incorporating all the information derived from different investigations, a subsurface model was synthetically simulated and generated 2D electrical resistivity response for different arrays and compared with the field responses to further validate the geoelectrical response of deep aquifer setup associated with lineament.

An integrated study was carried out to investigate the subsurface geological conditions in a hard rock environment, with the aim of identifying zones with groundwater resource potential. The study, in Bairasagara watershed, Karnataka, India, considered geomorphology, water level, resistivity imaging, self potential, total magnetic field and susceptibility. The signatures due to lineaments have been clearly identified and their role in groundwater movement has been documented. Synthetic simulation methods were used to model the electrical response of the lineament using finite differential modeling scheme. The inverted image of the field data is compared with the synthetic image and iteration were performed on the initial model until a best match was obtained resulting on the generation of the calibrated resistivity image of the subsurface. Resistivity imaging revealed that the dykes are weathered/fractured to a depth of 6-8 m and are compact at deeper levels, and that they behave as barriers to groundwater movement, yet facilitate a good groundwater potential zone on the upgra- dient side. The results of magnetic surveys were utilized in differentiating granites and dolerite dykes with an insignificant resistivity contrast. Geomorphological expression alone cannot reveal the groundwater potential associated with a lineament. However, characterizing the nature of the feature at depth with integrated geophysical methods provides essential information for assessing that potential.Résumé Uneétude aété réalisée sur la géologique de sub-surface en milieu rocheux fracturé, avec pour objectif l'identification des zones possédant des potentiels de ressource en eau souterraine. Cetteétude, sur le bassin versant de Bairasagara, Karnataka, prend en compte la géomorphologie, le niveau de l'eau, les images de résistivité, le self potentiel, le champ magnétique total et la susceptibilité. Les signaux dusà la présence de linéaments, ontété clairement identifiés ainsi que leur influence sur le mouvement des eaux souterraines. Les méthodes de simulation synthétique ontété utilisées pour modéliser la réponsé electrique des linéaments, en utilisant une modélisation par différences finies. L'image inversée des données de terrain est comparée avec l'image synthétique; des itérations sur le modèle initial ontété mises en oeuvre jusqu'à un rapprochement optimal, résultant en la génération d'une image calibrée de la résistivité de la sub-surface. Les images de résistivités révèlent que les dykes sont altérés et fracturés sur une profondeur de 6à 8 mètres et sont compactésà des profondeurs plus importantes. Les dykes se conduisent dés lors comme des barrières au mouvement des eaux souterraines. Cependant ils favorisent un bon potentiel, du point de vue de la remontée des gradients. Les résultats des levés magnétiques ontété utilisés pour différencier les dykes de granite et les dykes de dolérite avec des contrastes de résistivité trop faibles. L'étude géomorphologique seule n'aurait pu suffireà comprendre le potentiel des eaux s...