| 摘要: | 河口及感潮河川是聯繫海洋與河川間之通道，河口區域是一個半封閉的沿海岸水體，與鄰近的海域自由流通，既具有內陸河流的特徵：如逕流流量的洪、枯水期等季節變化，又有海洋的部分特徵：如潮汐的漲落，故河口與感潮段的水動力與鹽度特性極為複雜，亦影響懸浮沉積物在此的傳輸作用。淡水河流域為台灣最大之感潮河川，包含大漢溪、新店溪、基隆河三大支流；本研究蒐集民國91、92年淡水河口至大漢溪及93年淡水河口至基隆河之觀測資料，其中包含高、低平潮量測與全潮觀測之鹽度與懸浮沉積物濃度。 應用三維水理與優養數值模式(Hydrodynamic-Eutrophication Model, HEM-3D)模擬淡水河口鹽度與懸浮沉積物之分佈，模式演算之邊界條件為：大漢溪、新店溪和基隆河上游給定流量、沉積物濃度，下游因處於外海，因此在東、西及北邊界給定潮位、沉積物濃度與鹽度。數值模式於水平方向採用正交曲線座標，垂直方向採用sigma座標系統。模式模擬結果以實測鹽度與懸浮沉積物濃度資料作為比對，以探討淡水河受外海潮汐及上游淡水流量作用時河口鹽度的分層現象及懸浮沉積物最大混濁度的區域；在模擬方面，對鹽度分層現象有較好的結果，最大混濁度也可以被表現出來。最後再對影響沉積物傳輸的相關參數進行敏感度分析，並應用於淡水河不受鹽度影響，以及底床無沉積物供應、風場對鹽分及懸浮沉積物之影響與平均流量作用之數值實驗，以探討其中水理及懸浮沉積物可能產生的變化。 Estuaries and tidal rivers are the primary conduit between river and coastal ocean. Estuaries are the semi-enclosed coastal water body which connects with the open sea, and they have the characteristics of inland river, such as flood and dry seasonal variations due to runoff. They also exhibit the characteristics of ocean, such as the flood and ebb tides. Therefore, the hydrodynamics and salinity characteristics of the estuary and tidal river are extremely complicated, and they also affect the transport processes of suspended sediment. The Danshuei River system is the largest estuary system in Taiwan and consists of three major tributaries: Tahan Stream, Hsintien Stream and Keelung River. In this study, the measured salinity and suspended sediment data including slackwater and intense surveys were collected in the periods of 2002 to 2004. The measured stations along the Danshuei River to Tahan Stream and Danshuei River to Keelung River were conducted, respectively, from 2002 to 2003, and in 2004. A real-time, three-dimensional Hydrodynamic-Eutrophication Model (HEM-3D) was performed and applied to simulate salinity distribution and transport of suspended sediment distributions in Danshuei River estuarine. The boundaries of upstream (i.e. the Tahan Stream, Hsintien Stream, and Keelung River) are specified with constant freshwater discharge, salinity (with zero), and suspended sediment concentration. The downstream boundary is extended to the adjacent coastal sea and specified with tidal elevation, salinity, and suspended sediment concentration. Governing Equations are formulated in curvilinear-orthogonal horizontal coordinates and a sigma vertical coordinate. The comparisons of simulated result and field measurement in salinity and suspended sediment distributions were used to investigate and analyze the salinity stratification phenomenon and estuarine turbidity maximum (ETM) in the estuarine system. Moreover, the model sensitivity analyses were used to identify the vital parameter in the suspended sediment transport model. Finally, the numerical experiments were conducted with no saline effect, no sediment supply from the sediment bed, wind stress effect, and the influence by mean freshwater discharge to comprehend the influence on residual current and suspended sediment distribution in the Danshuei River estuarine system. |
