Gradient profiling for the investigation of groundwater saturated fractures in hard rocks of Uttar Pradesh, India

Gradient profiling (GP) has been successfully utilized as a preliminary tool to identify fractured zones saturated with groundwater in hard-rock areas of Robertsganj, Sonebhadra district, Uttar Pradesh, India. Conducting geoelectrical sounding at randomly selected places may not provide fruitful results since fractures are sparsely distributed in hard rocks. In gradient profiling, current electrodes with large separation remain fixed while the potential dipole is moved between the current electrodes in the central one-third portion of the profile at a small station interval. A GP survey was conducted along seven profiles having different lengths in two small sectors of the study area. Low resistive zones have been identified which correspond to the fractured zones. A few geoelectrical soundings were carried out to investigate the depth and thickness of the fractured zones. Two test boreholes, one drilled in each sector, yielded continuous discharge of fresh water (18,000 24,000 L/h). The present study confirms the findings of previous work that the GP survey is a powerful initial technique that identifies the presence of a fractured zone, especially in a hard-rock area covered with a thin soil layer.