Abstract Hydraulic barriers using either two or three injection wells are studied analytically to evaluate their performance on improving groundwater extraction in a coastal aquifer under the threat of seawater intrusion. The multiple well system is operated by extracting fresh groundwater through a landward well and partially reinjecting into the aquifer through two or three wells located parallel to the coastline and between the interface toe and the extraction well. We found that with appropriate well locations and pumping rates, the multiple-well system could outperform a single extraction well in terms of net extraction rate, which is up to 90% higher for an aquifer with a thickness of 20 m, hydraulic conductivity of 10 m/d, and freshwater influx of 0.24 m2/d. Sensitivity analyses reveal that the monotonicity of the maximum net extraction rate is determined by the total injection rate. In specific, when the total injection rate is fixed, the maximum net extraction rate is a non-monotonic function of the distance between the injection well and the coastline and the distance between two injection wells, resulting in a global maximum. When the total injection rate is not fixed, by contrast, the maximum net extraction rate depends on the total injection rate, and a larger total injection rate leads to a larger maximum net extraction rate. By using different injection rates for side and middle injection wells of the three-injection-well hydraulic barrier, the maximum net extraction rate could be further improved, depending on the distance between the two injection wells. Analytical analyses can provide initial guidance for the design of a multiple-well system in coastal aquifers with the purpose of obtaining enhanced extraction under the threats of seawater intrusion.

中文翻译：

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评价多井水力屏障增强沿海含水层地下水提取的性能

摘要 分析研究了使用两个或三个注入井的水力屏障，以评估它们在海水入侵威胁下改善沿海含水层地下水提取的性能。多井系统的操作方式是通过陆上井抽取新鲜地下水，然后通过平行于海岸线且位于接口趾部和抽取井之间的两口或三口井将部分水重新注入含水层。我们发现，在适当的井位和抽水量下，多井系统在净采油率方面可以优于单采油井，对于厚度为 20 m、水力传导率为 10 的含水层，净采油率高出 90%。 m/d，淡水流入量为 0.24 m2/d。敏感性分析表明，最大净萃取速率的单调性由总注入速率决定。具体而言，当总注量固定时，最大净采出率是注水井距海岸线距离和两口注水井距离的非单调函数，导致全局最大值。相比之下，当总注入量不固定时，最大净抽取量取决于总注入量，总注入量越大，最大净抽取量也越大。通过对三注井水力屏障的侧注井和中注井采用不同的注油量，可以进一步提高最大净采油率，这取决于两注水井之间的距离。