Determination of Weathered Granite Resistivity from Electrical Resistivity Profiling Data using Empirical Relations

Methodology of groundwater prospecting in granitic terrains using electrical resistivity method sequentially consists of conducting profiling survey, selection of low apparent resistivity zones indicative of probable saturated regions, and estimating the resistivity and thickness of the weathered layer to determine its hydrogeological characteristics employing VES method.

In Musi Ayacut region, where a detailed survey was carried out for groundwater, one of the current electrodes (AB/2) separation used for profiling survey was 10 m. The apparent resistivity values obtained using the above separation were found to be indicative of the hydrogeological nature of the weathered granite layer in the area. It was observed that the apparent resistivity values obtained by the above separation ρa (AB/2= 10m) are linearly related to the true resistivity (ρ2) value of the weathered granite.

Using the above obtained statistical empirical relations, the weathered granite layer resistivity can be estimated from the profiling survey results even without conducting a large number of vertical electrical soundings in the area.