Confirmation of Nature of Palaeo-course of Assi River, India: Some Significant Revelations from Electrical Resistivity Tomography

ABSTRACT A long and continuous palaeo-course of Assi River, in between Prayagraj and Varanasi, in the Ganga River plains with indications of good groundwater potential had been traced from remote sensing data. Electrical Resistivity Tomography (ERT) has been conducted along eight lines for confirmation of the same palaeo-course in general and to specifically ascertain the nature of the course—the past flow conditions and the type of deposits. The variation in the thickness of channel deposits along the concave and convex banks and the middle parts is an indication of lean flow. The mixed fractions of channel deposits are an indication of dumping of sediments in the dying stages of a river. The ERT investigation has further helped in delineating the high resistive palaeo-channels (20 to 50 Ohm.m), the low resistivity aquiclude clay layer (<15 Ohm.m) and the deeper and relatively higher resistivity sandy layer (>50 Ohm.m), which could be the principal aquifer in the area.