Application of Electrical Imaging for Borehole Siting in Hardrock Regions of India

Much of the seventy five percent of India that is underlain by shallow granitic and gneissic basement suffers from a shortage of water, but it is precisely these areas where siting successful boreholes for water supply is a difficult problem. Geophysical methods, especially resistivity sounding, are commonly employed to improve the drilling success rate, but the techniques are time consuming, subject to considerable ambiguity and still have scope for considerable improvement. In the Dindigul area of Tamil Nadu, we have tested new electrical tomography (imaging) techniques to provide detailed 'pictures' of the sub-surface that show variations in bedrock topography and the nature and thickness of the overburden. The resulting images can be used to plan borehole investigations more cost effectively.