Groundwater-Surface Water Interactions in the Tidally-Dominated Coastal Region of the Bengal Basin: A One-Dimensional Numerical Analysis of Tidal and Surface Water Controls on Local Aquifer Systems

Abstract

Climate change and sea level rise will continue to stress the human and natural landscapes over the next century with low-lying deltaic regions characterized by extensive aquifer systems being highly vulnerable to these perturbations. Specifically, groundwater and surface water interactions may be adversely affected by the estimated rise (56-200 cm) in sea level through aquifer salinization. The Bengal Basin is one of the most densely populated of these regions with brackish groundwater already an issue in the tidally-dominated reaches near the Bay of Bengal. Previous studies suggest the groundwater system is isolated from the surface water system with the brackish groundwater being of Pleistocene age. Here, we employed a one-dimensional finite-difference model of a conceptualized aquifer system between two tidal channels in an attempt to discern groundwater and surface water connectivity. The model varied aquifer transmissivity (TA), channel transmissivity (TC), aquifer storativity (S), and tidal range (TR) over a realistic range of values. The dominant control on connectivity was found to be hydraulic diffusivity (TA/S and TC/S). The results suggest some degree of hydraulic connectivity between the aquifer and tidal systems is possible under present conditions. These results call for a reevaluation of our understanding of groundwater-surface water dynamics in the region and may influence our mitigation strategies in the face of climate change.