Characterizing Sedimentary Facies of Meandering Paleochannel and Floodplain Deposits using Multi-Frequency Ground Penetrating Radar: A Case Study from the Western Part of Bengal Basin

The sedimentary architectures of paleo-river channels and their associated floodplains play a crucial role in shaping alluvial aquifers. Meandering point bars, known for their high permeability, enhance groundwater recharge, while floodplains serve as natural filters, regulating both the vertical and lateral movement of groundwater. Geophysical methods, particularly Ground Penetrating Radar (GPR), facilitate high-resolution imaging of subsurface features, allowing for detailed mapping of sedimentary structures and hydrogeological characteristics. This study focuses on a paleo-meandering point bar and its adjacent floodplain deposits within a heterogeneous alluvial aquifer in North 24 Parganas, West Bengal. Four GPR survey sites were analyzed, three along the meandering channel axis and one on the adjacent floodplain, using 200 MHz and 80 MHz antennas to capture subsurface features up to a depth of 20 meters. Six radar facies (RF) and three types of radar bounding surfaces (RS) including chute channels, lateral accretion surfaces, and erosional surfaces were identified, corresponding to various sedimentary lithofacies. Towards the meandering apex, the paleochannels displayed well-defined, continuous, and horizontal subparallel RF indicative of top silty clay deposits that increase in thickness. In contrast, wavy, inclined, sub-horizontal RF indicates channel sand deposits, which exhibit a decrease in thickness toward the meander apex. The GPR profiles of the floodplain revealed sub-horizontal laminated RF, typical of finer silt and clay deposits at greater depths. The comparison of RF and RS at different scales highlights distinct depositional patterns between meandering channel deposits and floodplain sediments. This study emphasizes the importance of integrating multi-frequency GPR data to interpret sedimentary processes in fluvial-sedimentary environments, providing valuable insights into the sedimentary architecture and hydrogeological properties of the paleo-meandering system.