Delineation of Sedimentary Facies and Groundwater-Sea Water Disposition in an Intertidal Zone of the Bay of Bengal using GPR and VES

Abstract

A combination of geophysical study including ground penetrating radar (GPR) and vertical electrical sounding (VES) was done to identify different shallow-subsurface depositional features in an intertidal coast of the eastern parts of India, adjoining the Bay of Bengal (BoB) (Chandipur, Odisha state). The study was aimed to understand the variation of sedimentary depositional sequences, prograding to the ocean from land, as well as towards the confluence of a river channel with the BoB. Six VES points and 85 GPR traverses were taken in the intertidal flat. The data were calibrated with sedimentary sequences retrieved from simultaneously drilled boreholes in four locations. Resistivity data clearly demonstrate the subsurface sediment layer boundaries with water saturation variability, up to 156 m below ground surface (bgs). The data suggest thickening of brackish water saturated clay layers towards the southwestern part. GPR data were capable of resolving the geometry of intertidal dunes, buried palaeo-channels, erosional surface, water table, eolian deposit of sand, and washover delta depositional features which are all present in this study area. Several erosional surfaces, related to sedimentary processes, e.g., delta overwash processes, were clearly demarcated. The study also successfully identified and visualized the saline-fresh groundwater interfaces and submarine ground water discharge (SGD) zones. Consequently, based on these data, a conceptual model of the depositional and erosional history of the sedimentation of the area, as well as the coastal hydrogeological disposition, was conceived.