Integrated studies for characterization of lineaments used to locate groundwater potential zones in a hard rock region of Karnataka, India

Abstract

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...

Geophysical model of geological discontinuities in a granitic aquifer: Analyzing small scale variability of electrical resistivity for groundwater occurrences

“…Quartz reef is more susceptible for fissuring, whereas spheroidal weathering is common feature over dolerite. The earlier work of Chandra et al (2006) on ERT response over dolerite dyke intruded in granite indicates that the upper portion of such intrusive are weathered at shallow level (up to 8 m) reflected as low resistivity and further downward it is compact and shown as high resistivity.…”

“…Thus, for past few decades lineament mapping with remote sensing data especially in areas with igneous and metamorphic rocks of poor primary porosity (commonly referred as hard rock terrain) have been focus measurement for targeting well sites despite with varying success rates. Chandra et al (2006) studied lineament such as dolerite dyke and major fractures running along the river/ stream course and showed that lineament need not to be always potential or non potential to the groundwater. They have demonstrated that the geophysical characterization helps in understanding about the potentiality.…”

Electrical resistivity tomography applied to groundwater aquifer at downstream of Chih-Ben Creek basin, Taiwan

“…Two-dimensional ERT has been frequently applied to various geotechnical engineering projects since the rapid advancement in geophysical equipment and computer technology in the 1980s (Loke and Barker 1996;Dahlin and Loke 1998;Dahlin 2001;Dahlin and Zhou 2004;Cardarelli and Fischanger 2006). ERT enables rapid and accurate examinations of groundwater aquifers (Froese et al 2005;Khesin 2005;Takahashi et al 2006;Chandra et al 2006;Fowler and Moysey 2011), landslides (Jongmans et al 2000;Drahor et al 2006), fault investigations (Rizzo et al 2004), seawater intrusion (Nassir et al 2000;Sherif et al 2006), and landfills (Guerin et al 2004;Zume et al 2006).…”

The electrical resistivity method

“…For detecting subsurface anisotropy created by dipping or vertical structures like dykes, quartz reefs, joints or fractures, which are considered electrical as well as hydraulic conductivity discontinuities in hard rock, soundings at a point within the area of influence of such structures can be conducted in several radial directions, viz., Downloaded by [University of Cincinnati] at 07:21 04 June 2016 Figure 6.22 Electrical resistivity imaging in granitic terrain across (a) an exposed dyke (Source: Chandra et al, 2006) and (b) shallow fractured zone (Source: Bernard et al, 2006). E-W, N-S, NE-SW, NW-SE and/or any other directions at 10 • to 20 • interval covering 360 • .…”