Details of the Abstract
| Title of paper | Magnetotelluric Imaging of Deep Aquifers in Seawater-Intrusion Areas of the Ganges-Brahmaputra Delta, Bangladesh |
| List of authors | Le, H., Key, K., Steckler, M., Person, M., Sazeed, N., Bhuiyan, A. |
| Affiliation(s) |
Lamont-Doherty Earth Observatory Columbia University, Lamont-Doherty Earth Observatory Columbia University, Lamont-Doherty Earth Observatory Columbia University, New Mexico Institute of Mining and Technology, New Mexico Institute of Mining and Technology, Dhaka University |
| Summary | Marine incursions in the tidal dominated regions of the southwestern Ganges-Brahmaputra delta (GBD) exacerbate the challenge of freshwater access for agriculture and domestic uses. Furthermore, arsenic pollution and intensive aquifer extraction limit the potable water supply for high population-density areas. In SW Bangladesh, the shallow groundwater aquifer is saline leading to considerable water stress due to the lack of potable water during the dry season. Although tube wells and DC resistivity surveys have been conducted extensively to evaluate these saline shallow aquifers, they fail to assess the underlying deep groundwater systems. Here we apply the broadband magnetotelluric (MT) method to investigate the potential deep fresh aquifers along the Pusur River in SW Bangladesh from Khulna to the coast. The high-quality broadband MT responses reveal an extensive resistive freshwater distribution in the upper kilometer of the 120 km long profile. We use Archie’s law along with hydrogeologic constraints to estimate groundwater salinity. Our estimated salinity model shows a south-dipping freshwater wedge on the northern part of the profile and a smaller low-salinity body close to the river mouth. While these two deep freshwater bodies may connect with the groundwater recharge system, low flow rates and 14C age dates up to 30,000 years suggest that they are primarily the remnants of preserved Pleistocene groundwater. Based on Holocene sediment thickness data from tube wells, we suggest that the discontinuity between the two bodies is due to the NW-SE-oriented incised Ganges paleovalley that cut through the central part of the profile during the last sea-level lowstand. Our results provide the first detailed extent of deep fresh groundwater in coastal Bangladesh and salinity information relevant for planning of future deep wells in freshwater-stressed SW Bangladesh. |
| Session Keyword | 3.0 EM methods for exploration (geothermal, mineral resources, etc.) |
| File upload |
3.0_magnetotelluric_imaging_o_le_01.pdf
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