While tides of multiple constituents are common in coastal areas, their effects on submarine groundwater discharge (SGD) and salinity distributions in unconfined coastal aquifers are rarely examined, with the exception of a recent study that explored such effects on unconfined aquifers with fixed inland freshwater input. For a large proportion of the global coastline, the inland areas of coastal aquifers are topography-limited and controlled by constant heads. Based on numerical simulations, this article examines the variation of SGD and salinity distributions in coastal unconfined aquifers with fixed-head inland boundaries at different distances from the shoreline (i.e., 50, 100, 150, and 200 m). The results showed that the fluctuation intensity of freshwater input was enhanced as the inland aquifer extent decreased, e.g., the range of tide-induced fluctuations in freshwater input increased by around 5 times as the inland aquifer extent decreased from 200 to 50 m. The frequency spectra of the fluctuations of SGD and salinity distributions showed that the coastal aquifer of a shorter inland aquifer extent smoothed out fewer high-frequency tidal constituents but enhanced interaction among different tidal constituents. The interaction among tidal constituents generated new low-frequency signals in the freshwater input and salinity distributions. Regressions based on functional data analysis demonstrated that the inland freshwater input and salinity distributions at any given moment were related to the antecedent (previous) tidal conditions weighted using the probability density function of the Gamma distribution. The influence of the antecedent tidal conditions depended on the inland aquifer extent.

中文翻译：

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多成分潮汐对具有固定水头内陆边界的地下河口的影响

虽然多种成分的潮汐在沿海地区很常见，但它们对无承压沿海含水层的海底地下水排放 (SGD) 和盐度分布的影响很少被研究，但最近的一项研究除外，该研究探讨了对具有固定内陆淡水输入的无承压含水层的这种影响. 对于全球大部分海岸线，沿海含水层的内陆地区受地形限制并受恒定水头控制。本文基于数值模拟，研究了距海岸线不同距离（即 50、100、150 和 200 m）具有固定水头内陆边界的沿海非承压含水层中 SGD 和盐度分布的变化。结果表明，淡水输入的波动强度随着内陆含水层范围的减小而增强，例如，随着内陆含水层范围从 200 米减少到 50 米，潮汐引起的淡水输入波动范围增加了约 5 倍。SGD和盐度分布波动的频谱表明，内陆含水层范围较短的沿海含水层平滑了较少的高频潮汐成分，但增强了不同潮汐成分之间的相互作用。潮汐成分之间的相互作用在淡水输入和盐度分布中产生了新的低频信号。基于功能数据分析的回归表明，任何给定时刻的内陆淡水输入和盐度分布都与使用 Gamma 分布的概率密度函数加权的先行（先前）潮汐条件相关。