Insufficiency of potable water is acute in southwest (SW) coastal areas of Bangladesh. The local population ignores the depth to saltwater/freshwater interface causing many unsuccessful waters wells drilling. In this context, a combined use of borehole logs, geophysical well logs, vertical electrical soundings (VES), electrical resistivity tomography (ERT) and electrical conductivity (EC) of sampled waters was performed to identify saltwater/freshwater interface depths in this coastal part. The study shows that the depth to freshwater/saltwater interface varies from place to place occurring commonly between 190 to 285 m, and locally as shallow as 146 m. The shallow freshwater/saltwater interface depth is greatly influenced by the upconing of fresh water from the deep aquifer (DA) near the major rivers and coast compared to the landward part and is mixed with more saline waters above. Vertically infiltrated saltwater is the main cause of brackish water in the upper shallow aquifer (USA), which is hydraulically connected with the lower shallow aquifer (LSA), and not directly recharged from the Bay of Bengal in the south. The study will contribute to find out the depth of the potential freshwater aquifer and assess the aquifer vulnerability in the coastal area of SW Bangladesh.

中文翻译：

---

孟加拉国西南部沿海地区淡水-咸水界面的地球物理圈定

孟加拉国西南 (SW) 沿海地区的饮用水严重不足。当地居民忽视了咸水/淡水界面的深度，导致许多水井钻探失败。在此背景下，结合使用钻孔测井、地球物理测井、垂直电测深 (VES)、电阻率层析成像 (ERT) 和采样水的电导率 (EC) 来确定该沿海部分的咸水/淡水界面深度. 研究表明，淡水/咸水界面的深度因地而异，通常在 190 至 285 m 之间，局部最浅至 146 m。与陆地部分相比，浅层淡水/咸水界面深度受来自主要河流和海岸附近的深层含水层 (DA) 的淡水上锥影响很大，并与上方更多的咸水混合。垂直入渗的咸水是上部浅层含水层（美国）中微咸水的主要原因，该咸水与下部浅层含水层（LSA）通过水力连接，不直接从南部的孟加拉湾补给。该研究将有助于找出潜在淡水含水层的深度，并评估孟加拉国西南部沿海地区的含水层脆弱性。而不是直接从南部的孟加拉湾充电。该研究将有助于找出潜在淡水含水层的深度，并评估孟加拉国西南部沿海地区的含水层脆弱性。而不是直接从南部的孟加拉湾充电。该研究将有助于找出潜在淡水含水层的深度，并评估孟加拉国西南部沿海地区的含水层脆弱性。