In the polder region of coastal Bangladesh, shallow groundwater is primarily brackish with unpredictable occurrence of freshwater pockets. Delta building processes, including the codeposition of fresh‐to‐saline porewater and sediments, have formed the shallow aquifer. Impermeable clay facies and the lack of a topographical gradient limit the flow of groundwater and its mixing with surface water so controls on spatial variability of salinity are not obvious. By characterizing groundwater‐surface water (GW‐SW) interactions, this study attempted to identify areas of potable groundwater for the polder communities. We used transects of piezometers, cores, electromagnetic induction, and water chemistry surveys to explore two sources of potential fresh groundwater: (1) tidal channel‐aquifer exchange and (2) meteoric recharge. Fresh groundwater proved difficult to find due to heterogeneous subsurface lithology, asymmetrical tidal dynamics, extreme seasonal fluctuations in rainfall, and limited field data. Geophysical observations suggest substantial lateral variability in shallow subsurface conductivity profiles. Piezometers show varying degrees of tidal pressure attenuation away from the channels. Nevertheless, the active exchange of freshwater appears to be limited due to low permeability of banks and surface sediments. Results indicate that pockets of fresh groundwater cannot be identified using readily available hydrogeological methods, so alternative drinking water sources should be pursued. By better understanding the hydrogeology of the system, however, communities will be better equipped to redirect water management resources to more feasible and sustainable drinking water options.

中文翻译：

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在孟加拉国沿海咸水层中寻找淡水

在孟加拉国沿海的田地区，浅层地下水主要是微咸的，淡水袋的发生是不可预测的。三角洲的建造过程，包括新鲜到咸水的孔隙水和沉积物的共存，已经形成了浅层含水层。不可渗透的粘土相和缺乏地形梯度限制了地下水的流动及其与地表水的混合，因此对盐度空间变异性的控制并不明显。通过表征地下水-地表水（GW-SW）的相互作用，本研究试图确定田的饮用水区域。我们使用了压力计，岩心，电磁感应和水化学调查的样板，探索了潜在的新鲜地下水的两种来源：（1）潮汐通道-含水层交换和（2）大气补给。由于地下非均质岩性，不对称的潮汐动力学，降雨的极端季节性波动以及有限的田间数据，事实证明很难找到新鲜的地下水。地球物理观测表明，浅层地下电导率剖面存在较大的横向变化。测压仪显示远离通道的潮汐压力衰减程度不同。然而，由于堤岸和表层沉积物的低渗透性，淡水的主动交换似乎受到限制。结果表明，使用现成的水文地质方法无法识别出新鲜的地下水，因此应寻求替代的饮用水源。通过更好地了解系统的水文地质学，