Assessment of Geology and Hydro-geology Using ERT (Electrical Resistivity Tomography) at Barisal, Bangladesh.

Ganges Brahmaputra Delta is the world largest delta in the world. The sediment pile is about 22 km thick in this region which is a wonder in present world depositional system and the highest amount in this world. The depositional system has both fluvial and tidal effect. This combined depositional sequence is thick pile of alternating sand, silt and shale layer. Deposition rate is also very high in Ganges Delta. Barisal, a southwest division of Bangladesh is around 100 km off from the Bay of Bengal which is affected by tidal flood. The tidal range is up to 100 cm in vertical measurement. The top 30 m lithology of Barisal is dominated with shale and silt. There is also interbedded fine sand. People are facing salinity problem in their drinking water. Electrical resistivity (ERT) survey will measure the resistivity of subsurface soil or rock layer along with the pore space fluid. The overall resistivity of a rock layer shows how it opposes the flow of electric current through the layer. Two boreholes will be dug at two end of each survey line to cross-check the ERT data. Dipole-dipole electrical resistivity array will be used which is best for lithology differentiation. Earth imager 2D software will be used to process the ERT data and ArcGIS software will be used to generate maps. ERT survey will help to get a good resolution lithology as well as water quality data up-to 100 m depth. This work will aid the future plan to recognize freshwater aquifer zone as well as to develop disaster mitigation plan from the updated lithology. The compilation of all data will be used to construct lithological map and geological map Assessment of suitable aquifer depth, and seasonal changes in aquifer properties in term of drinking purpose will also be prepared of this rapidly changing depositing area.