Groundwater-Surface Water Interactions in the Poldered Landscape of Southwest Bangladesh

Bangladesh is shaped by the largest and most active delta system in the world. The Ganges, Brahmaputra, and Meghna river networks carve the low lying deltaic plains of the southern part of the country. Much of the tidal mangrove forest ecosystem of the lower delta was converted to poldered islands that sustain a Bangladesh population of 150 million though shrimp farming and rice production. These polder inhabitants lack potable water resources due to pathogen laden surface water and saline groundwater. This study examines polder groundwater-surface water interactions of fresh and saline water sources. Preliminary sampling of the polder groundwater suggests unpredictable apportioning of freshwater in the brackish aquifer. Using a broadband electromagnetic induction technique, we examine the conductivity profile of the shallow subsurface stratigraphy to identify potential rainwater recharge sites. Transects of nested piezometers, equipped with conductivity, temperature, and depth sensors, help determine the extent of tidal channel-aquifer interactions. Lithology from cores indicates that a highly variable clay cap likely regulates recharge. A better understanding of groundwater-surface water interactions will aid in the search for potable groundwater.