Delineation of Fractured Aquifer Using Numerical Analysis (Factor) of Resistivity Data in a Granite Terrain

In hard rock terrain, fractured aquifers comprise the major source of groundwater availability where the phreatic aquifer is de-saturated. It is essential to understand the interconnectivity between phreatic aquifer and deep fractured aquifer, for better water management strategy. Identification of fracture zones in hard rock terrain and potential groundwater source delineation had been a perennial problem in hydrology in the recent past. In concurrence to this, understanding the groundwater flow through fracture system has also been a challenge to hydrologists and geophysicists. The purpose of this paper is to highlight the study executed over a small watershed area, in a granite terrain, wherein an attempt was made to delineate and map the fractured aquifer using numerical (factor) analysis of the conventional vertical electrical sounding (VES) data. Delineation of fracture zones at depths and mapping their geometry were obscure due to limitations in 1D interpretation of VES data through curve matching technique. Factor analysis for the same VES data was carried out and as a result, fractured granite aquifer was deciphered. Also, based on the factor analysis, a fault was deciphered in the study area bifurcating the fractured aquifer into two segments which was later confirmed based on satellite photo data and 2D resistivity imaging survey. This numerical approach of resistivity data interpretation in concatenation with resistivity imaging or other techniques would prove to be an effective tool in groundwater exploration.