An Integrated Geophysical Approach for Groundwater Prospecting: A Case Study from Tamil Nadu

Delineation of groundwater resources in hard rock terrains is one of the important topics to be treated with a more advanced approach than simple one-dimensional attitude, particularly when looking for deeper water saturated horizons. The present study introduces an integrated geophysical approach to identify structural features such as fractures, weak zones and intrusive dyke bodies, which can control and host potable groundwater at greater depths. The study is conducted in an area of about 8 km² along east coast of Tamil Nadu, which has been identified as a major rainshadow zone. Geophysical measurements were carried out in very closely spaced grids making use of resistivity, magnetic and electromagnetic techniques. The sensitivity of each technique to different rock properties in varying directions has been considered to resolve the problem. A major weak zone running in SW-NE direction is demarcated which is characterised by many intrusive dyke bodies. The conductivity distributions at different depths throw light on many structural features. The varying thickness of weathered rock calculated from the Horizontal Loop Electromagnetic (HLEM) and Deep Resistivity Sounding (DRS) studies for the entire area reflects the extension of weathering associated with dyke emplacements. Geo-electrical sections obtained through DRS studies, concentrated mainly along the weak zone have shown the occurrence of potable groundwater resource controlled by structural features.