海淡水在沿海含水層的交互作用主要為由潮汐震盪、波浪與海淡水間密度差所引 起的自然現象。在複雜水文地質作用的影響下，沿海含水層的海淡水交互作用便成為 了水文循環中的一個顯著的部分。本研究利用在潮汐作用下，海淡水交界間過渡地帶 的時空分布的模擬來確認海淡水間的交互作用特性。為了達到此目的，本研究採用現 地調查與二維 SEAWAT 數值模式兩種工具，以進行桃園沿岸系統的地下水流場與溶質 傳輸的研究。此外，本研究亦利用時序分析辨別本含水層系統在潮汐影響下的反應特 性，並將其結果用來率定數值模擬結果。根據時序分析結果，本研究場址的地下水流 特性與潮汐息息相關，潮汐在本地的影響距離甚至能達到離岸約 400 公尺的地方。多點 觀測結果顯示潮汐造成研究區域內地下水的週期性震盪，頻率分析結果顯示該震盪的 振幅會隨著離岸距離的增加而指數下降，相位延遲則隨著離岸距離而有線性上升的現 象。
數值模擬方面，除證實了本研究所建立模型與現地觀測互相吻和外，本研究亦發 現由於本地複雜的海灘地形，潮汐的震盪與地下水源對於過渡地帶的影響並不明顯， 降雨大小的變化亦只造成地下水位面的改變。本研究另外亦發現陸地的補注量與進入 海中的地下水量成正比關係。

The interaction between seawater and freshwater is a natural process driven primarily by tidal oscillation, waves, and density variation between fresh groundwater and seawater in the coastal aquifer. Due to complex hydrogeology in the coastal aquifer, the dynamic of this interaction becomes a significant component of the hydrology cycle. Also, to determine the characteristics of the relationship between fresh groundwater and saltwater in this research, we aim to simulate the spatiotemporal of a transition zone between groundwater and seawater, induced by tidal fluctuation. Field investigations and SEAWAT two-dimensional numerical model were conducted to study groundwater flow and solute transport in the nearshore system located at the Taoyuan coast, the Northwest of Taiwan. Also, time series analysis is used to identify a characteristic of the aquifer system that responded to ocean tide. Then results are used to calibrate with the numerical simulation. According to the time series analysis results, the groundwater level fluctuates following the tidal period, and tidal effects on the groundwater level reached up to 400 m inland from the coast. Field observation at various locations showed that tide induced groundwater level changes periodically. Frequency analysis suggested that the fluctuation amplitudes decreased exponentially, and phase lag increased linearly for primary tidal signals as they propagated inland.
Moreover, the simulation results indicated that simulated groundwater levels were in good agreement with the observed data. The effects of fluctuation driven by the ocean tide and inland heads on the transition zone were relatively slight due to complex beach morphology. Besides, the different amount of groundwater discharge is to considered as changing water table elevation. As a result, when the inland head increased, the groundwater discharge amount also increased compared to the base case. Otherwise, this amount was dropped in case of decreasing the head.

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