Application of electrical resistivity to map the stratigraphy and salinity of fluvio-deltaic aquifers: case studies from Bangladesh that reveal benefits and pitfalls
Application of electrical resistivity to map the stratigraphy and salinity of fluvio-deltaic aquifers: case studies from Bangladesh that reveal benefits and pitfalls
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DOI：
10.1007/s10040-021-02342-y
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发表时间：
2021-04
影响因子：
2.8
通讯作者：
Micaela N. Pedrazas;M. Cardenas;A. Hosain;Cansu Demir;Kazi Matin Uddin Ahmed;S. H. Akhter;Lichun Wang;S. Datta;P. Knappett
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文献类型：
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作者：
Micaela N. Pedrazas;M. Cardenas;A. Hosain;Cansu Demir;Kazi Matin Uddin Ahmed;S. H. Akhter;Lichun Wang;S. Datta;P. Knappett
河流三角洲含水层是孟加拉国人民的主要饮用水来源。构成恒河-雅鲁藏布江-梅克纳三角洲的这些含水层在水文地质上是不均匀的。由于孟加拉国普遍存在地下水质量问题，了解水文地层结构和水化学至关重要，因为一些含水层单元受到污染，而其他含水层单元则是安全的。地球物理方法提供了一个潜在的有效和非侵入性的方法，这些含水层的广泛特性。本研究应用并研究了使用电阻率成像（ERI）绘制梅克纳河附近含水层-弱透水层系统的水文地层和盐度的局限性。一些电阻率（ER）截面显示出电阻率与晶粒尺寸之间的良好相关性。这些都表明，ERI是一个强大的工具，用于映射内部含水层结构及其边界与细粒弱透水层，显然出现低ER区。然而，在某些ER部分的部分，在电气性能的变化是由孔隙水电阻率。在这些情况下，低ER表示盐水，并不表示存在细颗粒物质，如淤泥或粘土。因此，检测到以下具有不同渗透率的水文地层带：（1）淡水饱和含水层，（2）区域性粉土/粘土弱透水层，（3）较深的盐水饱和地层。此外，在河流附近和渗流带下方检测到浅淤泥/粘土袋。因此，ERI是一种很有前途的技术，映射含水层与弱透水层，然而，观察很容易混淆孔隙水盐度。在这种情况下，钻孔资料和地下水盐度测量对于地面实况调查是必要的。
Fluvio-deltaic aquifers are the primary source of drinking water for the people of Bangladesh. Such aquifers, which comprise the Ganges-Brahmaputra-Meghna Delta, are hydrogeologically heterogeneous. Because of widespread groundwater quality issues in Bangladesh, it is crucial to know the hydrostratigraphic architecture and hydrochemistry, as some aquifer units are contaminated, whereas others are safe. Geophysical methods provide a potentially effective and noninvasive method for extensive characterization of these aquifers. This study applies and investigates the limitations of using electrical resistivity imaging (ERI) for mapping the hydrostratigraphy and salinity of an aquifer-aquitard system adjacent to the Meghna River. Some electrical resistivity (ER) sections showed excellent correlation between resistivity and grain size. These suggest that ERI is a powerful tool for mapping internal aquifer architecture and their boundaries with finer-grained aquitards which clearly appear as low-ER zones. However, in parts of some ER sections, variations in electrical properties were determined by porewater resistivity. In these cases, low ER was indicative of brine and did not indicate the presence of finer-grained materials such as silt or clay. Accordingly, the following hydrostratigraphic zones with different resistivities were detected: (1) aquifers saturated with fresh groundwater, (2) a regional silt/clay aquitard, and (3) a deeper brine-saturated formation. In addition, shallow silt/clay pockets were detected close to the river and below the vadose zone. ERI is thus a promising technique for mapping aquifers versus aquitards; however, the observations are easily confounded by porewater salinity. In such cases, borehole information and groundwater salinity measurements are necessary for ground-truthing.