The interaction between freshwater and saltwater in the mixing zone governs regional groundwater flow and the exchange of water and salt between groundwater and the ocean. However, previous studies have overlooked the impact of land reclamation on the transient behavior of the mixing zone. This research investigated the dynamic influence of reclamation length, reclamation material properties, and recharge rate on the transient behavior of the mixing zone and timescale of mixing zone variation (TMV) through a series of field-scale numerical simulations. In general, the width of the mixing zone (WMZ) in the upper and center regions of the aquifer exhibited initial increase followed by subsequent decrease in various scenarios, displaying a consistent trend. For reclamation lengths less than 300 m, the mixing zone reached a steady-state condition within 8,000 days, while the corresponding TMV for a 500 m-length reclamation case increased to 20,000 days. The growth rates of the WMZ in the upper and center regions of the aquifer were notably slower, requiring more time to reach steady state in low-permeability scenarios. This observation underscored that reclamation with lower permeability could significantly extend the TMV. It was noteworthy that varying the longitudinal dispersion of the reclamation area between 0.5–10 m had only a slight effect on the TMV, ranging from 8,000 to 8,500 days. The peaks of the mixing zone width showed a proportional increase with longitudinal dispersion. Furthermore, increasing the recharge rate led to a substantial decrease in the TMV, from 10,000 days to 2,000 days. The WMZ exhibited faster growth with increasing recharge rate.

中文翻译：

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沿海含水层围垦后淡水-咸水混合带的瞬态行为


混合区淡水和咸水之间的相互作用控制着区域地下水流以及地下水和海洋之间的水和盐的交换。然而，先前的研究忽视了土地复垦对混合区瞬态行为的影响。本研究通过一系列现场尺度数值模拟，研究了填海长度、填海材料特性和回灌率对混合区瞬态行为和混合区变化（TMV）时间尺度的动态影响。总体而言，含水层上部和中部的混合带宽度（WMZ）在各种情况下均呈现先增大后减小的趋势，表现出一致的趋势。对于填海长度小于300 m的情况，混合区在8,000天内达到稳态条件，而对于500 m长度的填海情况，相应的TMV增加到20,000天。含水层上部和中部区域的 WMZ 增长速度明显较慢，在低渗透率情况下需要更多时间才能达到稳定状态。这一观察结果强调，渗透率较低的填海工程可以显着延长 TMV。值得注意的是，填海区纵向分散在0.5-10 m之间变化对TMV的影响很小，范围为8,000到8,500天。混合区宽度的峰值显示出随着纵向分散成比例增加。此外，增加充值率导致TMV大幅下降，从10,000天减少到2,000天。随着补给率的增加，WMZ 表现出更快的增长。