Flow-direction-dependent (FDD) dispersivity in coastal aquifers (CAs) may strongly affect the inland extend of seawater intrusion (SWI) and the accompanying vertical salinity distribution. FDD dispersivity may predict greater inland intrusion of the saltwater wedge, but less vertical spreading of salinity than does the classical flow-direction-independent (FDI) dispersivity, the standard currently employed in most numerical CA models. Dispersion processes play a key role in the SWI process and directly affect CA pumped water quality. Constant FDI dispersivities may be inappropriate in representing mixing processes due to large differences between depth and horizontal salinity transport scales, and due to typical structured heterogeneities in aquifer fabrics. Comparison of FDI and FDD model forecasts for the classical Henry problem (HP) steady-state SWI, based on a new HP semianalytical solution with FDD and on a numerical FDI model modified to additionally represent FDD, highlights the theoretical types of differences implied by these alternative dispersivity assumptions and exactly how each parameter affects the solution. Large differences between FDI and FDD dispersivity forecasts of time-dependent SWI in large scale heterogeneous aquifers occur in a typical CA (Akkar CA, Lebanon). The FDD model forecasts that future salinities in pumping wells will exceed the potable water limit, whereas the FDI model greatly underestimates the historic inland intrusion of the saltwater wedge and forecasts no impact on future Akkar CA potable water supply. These results indicate the importance of employing the appropriate dispersion process representation when creating model-based SWI forecasts, especially for developing effective CA management strategies.

中文翻译：

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流向依赖分散性对沿海含水层海水入侵的影响

沿海含水层 (CAs) 中的流向依赖 (FDD) 分散性可能强烈影响海水入侵 (SWI) 的内陆延伸和伴随的垂直盐度分布。FDD 分散性可以预测盐水楔的更大内陆侵入，但盐度的垂直扩散比经典的流向无关（FDI）分散性（目前在大多数数值 CA 模型中使用的标准）更少。分散过程在 SWI 过程中起着关键作用，并直接影响 CA 抽水水质。由于深度和水平盐度传输尺度之间的巨大差异以及含水层结构中典型的结构化异质性，恒定的 FDI 分散性可能不适合表示混合过程。经典亨利问题 (HP) 稳态 SWI 的 FDI 和 FDD 模型预测的比较，基于 FDD 的新 HP 半解析解和修改为额外表示 FDD 的数值 FDI 模型，突出了这些隐含的理论差异类型替代分散性假设以及每个参数如何影响解决方案。在典型的 CA（Akkar CA，黎巴嫩）中，FDI 和 FDD 对大规模非均质含水层中随时间变化的 SWI 弥散性预测之间存在很大差异。FDD 模型预测抽水井中的未来盐度将超过饮用水限制，而 FDI 模型大大低估了盐水楔的历史内陆入侵，并预测对未来的 Akkar CA 饮用水供应没有影响。