Insights of 2-D Electrical Resistivity Tomography (ERT) for palaeo-channels and multi-aquifer dispositions in a morphodynamic system of the Ganga basin

Abstract

Abstract Deducing palaeo-channels, mapping its boundaries, and structure of multi-aquifer disposition are essential for groundwater management. Because it helps to augment groundwater resources by acting as recharge channels, knowing the disposition of multi-aquifer system. Thus, a high-resolution electrical resistivity tomography (ERT) survey was conducted to delineate these palaeo-channels and multi-aquifer in a morphodynamic system (area: ~521 km2) of the Ganga basin, northern India. This deposit comprises various grades of fine, medium, coarse, and gravelly sands which constitute the groundwater reservoir within the thick alluvial (~ 770 m) overlies on the Precambrian basement. The whole 19 ERT profiles were carried out with the spacings of 320–480 m using Wenner-Schlumberger configuration with the help of IRIS Syscal R1+ Instrument, France made. The field data were inverted into true the resistivities of the stratified layers using the RES2DINV vs. 3.71 Geotomo software, applying the smoothness-constrained least-squares optimization approach. The results indicate that the palaeo-channel resistivities vary from 20–60 Ω-m depending upon the water saturation in the sand horizons with a thickness of 4 to 40 m. It is nicely correlated with the borehole litho-logs. The deduced palaeo-channels are mainly oriented in the E-W and NE-SW directions, with a lateral extend of 40-200m at some places. On the palaeo-channels, the sediments are associated with comparatively high resistivities in the shallower part as compared to the top capping clay layer of the first principal aquifer, explored the depth of up to 90 m, bgl indicating the predominance of sand/sandy clay. These could be more productive and also form the recharge zones to the first principal aquifer.