Freshwater injection is a practical and efficient solution to mitigate seawater intrusion in coastal aquifers, but its thermal impacts on groundwater flow and salt transport are still poorly understood. This study investigates the dynamic characteristics of salinity distributions and seawater recirculation in coastal unconfined aquifers subjected to freshwater injection and tides. The results show that the seaward development of thermal plume modifies the transience of upper saline plume and saltwater wedge, significantly prolonging the aquifer response to injected freshwater. Three temporal variations of upper saline plume due to freshwater injection are driven by pressure waves of injected freshwater, thermal plume-induced changes of hydraulic gradients and saltwater wedge, and the hydraulic conductivity within the upper saline plume. Moreover, a delayed reduction in seawater recirculation in response to the thermal impacts of cold-water injection induces a significant and long-lasting overshoot of total water efflux. An increased tidal amplitude facilitates thermal effects on flow and salinity distributions. A deeper injection well extends the flow path of injected freshwater and thermally regulates discharge rates along the beach surface, thereby enhancing overshoot magnitude of total water efflux. These results improve the understanding of underlying processes related to freshwater injection in coastal aquifers and provide guidance for better managing coastal groundwater resources.

淡水注入是减轻沿海含水层海水入侵的一种实用而有效的解决方案，但其对地下水流动和盐分输送的热影响仍知之甚少。本研究调查了受淡水注入和潮汐影响的沿海非承压含水层中盐度分布和海水再循环的动态特征。结果表明，热羽流的向海发展改变了上层咸水羽流和咸水楔的瞬变，显着延长了含水层对注入淡水的响应。由于淡水注入引起的上层盐水羽流的三个时间变化是由注入淡水的压力波、热羽流引起的水力梯度和盐水楔的变化以及上层盐水羽流内的水力传导率驱动的。而且，为响应冷水注入的热影响，海水再循环的延迟减少导致总水外流显着和持久的过冲。增加的潮汐幅度促进了对流量和盐度分布的热效应。较深的注入井延长了注入淡水的流动路径，并通过热调节海滩表面的排放率，从而提高了总水流量的超调幅度。这些结果提高了对与沿海含水层淡水注入相关的潜在过程的理解，并为更好地管理沿海地下水资源提供了指导。增加的潮汐幅度促进了对流量和盐度分布的热效应。较深的注入井延长了注入淡水的流动路径，并通过热调节海滩表面的排放率，从而提高了总水流量的超调幅度。这些结果提高了对与沿海含水层淡水注入相关的潜在过程的理解，并为更好地管理沿海地下水资源提供了指导。增加的潮汐幅度促进了对流量和盐度分布的热效应。较深的注入井延长了注入淡水的流动路径，并通过热调节海滩表面的排放率，从而提高了总水流量的超调幅度。这些结果提高了对与沿海含水层淡水注入相关的潜在过程的理解，并为更好地管理沿海地下水资源提供了指导。