| 摘要: | 桃園台地區域過去因造山運動與多次海進海退，形成特有的含水礫石層上覆泥層，這類特殊的地質特徵從內陸延伸到海岸帶，甚至可能綿延至海岸線外，根據水平衡分析的結果，流往近海的地下水出流量非常可觀，暗示桃園海岸帶具有豐沛的地下水資源，近海可能有海洋地下水出流(SGD, Submarine groundwater discharge)的存在，本研究結合地下水水質資料與地電阻影像法觀測結果了解桃園新屋海岸帶的地下水鹽度時空變化，此外，我們根據取自新屋臨海工作站的岩心地層柱與臨近水文地質井資料建立水文地質模型，使用HYDROGEMCHEM4.3耦合數值模式進行二維地下水流與鹽度數值模擬，透過現地觀測資料與模擬結果的比較，探討新屋海岸帶的地下水流機制與海淡水特徵，分析與比較三種研究工具的優缺點與差異。根據本研究結果總結出以下幾點：(1)新屋海岸帶的地層存有大量的淡水出流量，淡水流可延伸至海岸帶外數百米後從海床下流出，說明此區存有海岸帶地下水出流(SGD, Submarine groundwater discharge)。(2)海岸帶地下水鹽度因潮汐現象而有週期性變化，此外，不同深度地層的地下水有不同的鹽度。(3)海灘區域與近岸陸地區域不同的地下水鹽度與水位之關係，推測與淡水的來源不同有關。(4)表層泥的存在使海岸地下水出流具有低流速、低鹽度與延伸範圍廣的特徵，未來建議可於桃園海岸帶區域進行SGD相關的地球化學與海岸生態研究，理解海岸帶的生地化與演化特徵，同時，也期望此篇研究之結果可作為水利單位評估桃園海岸帶地下水資源與永續利用的參考依據之一。;In the Taoyuan Plateau region, the unique aquifer with gravel overlain by a thin mud layer, which extends from the inland to the coastal zone and may even continue beyond the coastline was formed due to tectonic movements and repeated marine transgressions and regressions in the past. According to the results of the water balance analysis in the Taoyuan City, the significant outflow rate of groundwater towards the nearby sea suggests that it has abundant of groundwater resources in the coastal zone of the Taoyuan, and there may be Submarine Groundwater Discharge (SGD) occurring near the coastline. This study tried to understand spatiotemporal variation of salinity of groundwater in the coastal zone of Xinwu, Taoyuan combined the data of quality of groundwater and the result obtained by electrical resistivity tomography (ERT) method. Furthermore, we established the hydrogeological model based on the core stratigraphic column and hydrogeological well data obtained from the Xinwu Coastal TaiCOAST work station, conducting a HYDROGEOCHEM 4.3 two-dimensional variably saturated groundwater flow numerical simulation. By comparing between measured and simulated data, we explored the characteristics of underground seawater and freshwater and mechanisms of groundwater flow in the coastal zone of Xinwu, discussing the advantages, disadvantages, and differences of three study methods. The following conclusions based on the results can be listed: First, there was a significant amount of freshwater in the stratigraphy of the Xinwu coastal area, and the freshwater flow could extend hundreds of meters into the coastal zone before flowing out through the seabed, indicating the presence of submarine groundwater discharge (SGD) in this area. Second, the salinity of groundwater in coastal zone had periodic variation due to the tidal effect. In addition, different salinity of groundwater was measured in the groundwater at different depths. Third, we inferred that the difference relationship between groundwater salinity and water level between the beach and the nearshore area result from distinct sources of inland fresh groundwater. Third, the existence of a thin mud layer contributes to the characteristics of lower velocity, lower salinity and wider extended range of coastal groundwater outflow. It is recommended that future studies on SGD-related geochemistry and coastal ecology can be conducted in the nearshore area of Taoyuan to confirm the reality and impact of SGD. Additionally, we hope that the results of this study can serve as one of the reference for water resources management departments to evaluate the groundwater resource and sustainable use of groundwater in the Taoyuan coastal area. |
