Geo-Electrical Resistivity Survey for Freshwater Aquifer Delineation: A Case Study in Coastal Areas of Barguna District, Bangladesh

Salinity intrusion has severely impacted groundwater quality in the coastal region of Bangladesh particularly in the Barguna district. This salt intrusion is creating a pressing need for the identification of new freshwater sources. The presented work aims to delineate the subsurface aquifer system and identify potential zones for freshwater extraction using geo-electrical resistivity surveys. Vertical Electrical Sounding (VES) with the Schlumberger array was conducted at multiple sites across the study area. A total of twelve VES points were acquired and processed using computer-assisted inversion techniques, with interpretation validated against borehole lithologs. The results indicated that the subsurface geology is highly heterogeneous, with alternating sand and clay layers indicating frequent facies changes. The resistivity profiles suggest a three-tier aquifer system similar to models developed for other coastal regions of Bangladesh. The first aquifer lies at shallow depths ( 20 Ωm suggest the presence of limited freshwater pockets, which are spatially restricted and discontinuous. The third aquifer, generally starting below 220 m, is regionally extensive and represents the most promising freshwater source. However, reduced resistivity values in parts of Patharghata Upazila indicate possible saline intrusion even at these depths, imposing spatial constraints on deep freshwater development. The outcomes of this work will provide a basis for identifying suitable and unsuitable zones for groundwater development. Overall, the results demonstrate that freshwater availability in the region is strongly depth-dependent and geographically variable, emphasizing the need for site-specific groundwater abstraction planning in coastal Bangladesh.