Application of electrical imaging for borehole siting in hardrock regions of India

Around seventy-five percent of India is underlain by granitic and gneissic basement rocks with a thin covering of weathered material. Many of these areas are semi-arid to arid and do not have high enough rainfall to support agriculture throughout the year. Here, groundwater is not difficult to find as the water table is generally within 10 m of the ground surface; however, the yield of boreholes is frequently low and supplies do not have long-term sustainability, so it is important to locate boreholes in the most productive areas possible. One of the methods found to increase the efficiency and effectiveness of borehole siting investigations is geophysics, with electrical imaging becoming an increasingly popular survey technique. Here we present the results of trials of a manual imaging system applied to groundwater investigations in the Dindigul area of Tamil Nadu and show how electrical imaging can provide much more meaningful and reliable data than is possible with other types of survey. It is the first use of electrical imaging in borehole siting investigations in India.