An integrated study of electrical resistivity tomography and infiltration method in deciphering the characteristics and potentiality of unsaturated zone in crystalline rock

Abstract

To assess the shallow subsurface conditions in a granitic terrain, Electrical Resistivity Tomography (ERT) and double ring infiltrometer studies were conducted in Hyderabad city, India. Electrical Resistivity Tomography responses were monitored continuously with, Wenner and Schlumberger array with an electrode spacing of 1 and 5 m. Double ring infiltrometer hydrogeological test was equally done on the same ERT profile to image the subsurface resistivity distribution for shallow depths only. ERT has exemplified highly weathered and weathered zones and the infiltrometer study illustrated, the rate at which the water is infiltrating from the topsoil to the subsurface weathered zone. The data acquired from ERT and infiltration tests were analyzed and it is depicted that the rate of infiltration is increasing gradually concerning time i.e. at the 100th minute there is an anomaly showing a rapid increase in the rate of infiltration and the same is revealed in its depth calculation graph. Results indicating that the infiltrated water is tending to flow laterally rather than vertical, up to a depth of 17 m, thus concluding that this zone might be dominated by sheeting joints which play a vital role as a water carrier to enhance groundwater quality as well as quantity. These sheeting zones are generally flat, sometimes curved and nearly parallel to the topographic level which is formed mainly in granitoid rocks. A comprehensive study reveals the near surface information and its potentiality in terms of groundwater recharge. The findings and approach has implication towards selecting suitable sites and implementing best recharge techniques to improve the aquifer condition in all the sectors and can be upscale on a regional level in granitic terrain. Keywords: ERT, Double ring infiltrometer, Sheeting joints, Unsaturated zones, Hyderabad, India