| 摘要: | 淡水河系為台灣最大之感潮河川，其感潮河段包括三大支流，分別是大漢溪、新店溪及基隆河。河口及感潮河段為河川流域與近岸海洋水和物質交換所必經之道，所以對於此一河川水理狀況之瞭解可幫助預測污染物質自河川排放至近海的傳輸過程。河川與河口之重金屬污染物主要包含兩種型態：溶解態及顆粒態。後者是吸附於懸浮泥砂上的重金屬，一般是以分佈係數決定兩者之間佔有的比例。 為瞭解重金屬於河川與河口傳輸之物理現象，本研究採用垂直二維水動力、鹽度及懸浮泥砂傳輸模式為基礎，發展重金屬傳輸模式。模式應用區域以台灣最大的感潮河川—淡水河為研究對象，模擬其重金屬銅的傳輸，並計算淡水河之總重金屬銅、顆粒態銅及溶解態銅三種型態之濃度。模式演算時上游邊界分別是：城林橋附近（大漢溪）、秀朗橋上游（新店溪）以及五堵水文站（基隆河），淡水河出海口為下游邊界。比較各測站之實測與模擬結果之水位、流速、流量和鹽度以及懸浮泥砂濃度之時間序列變化後，顯示垂直二維水理與懸浮泥砂傳輸模式之正確性，再利用模式模擬之重金屬銅濃度與國家海洋科學中心於民國90年至91年期間兩次重金屬銅的觀測資料進行比較，以確定重金屬傳輸模式之準確性。由現場拍攝照片及環保署與海洋科學中心觀測資料可發現新海橋附近有明顯污染產生，因此在模式中需於新海橋附近假設一點源污染排入（250 kg/day）才能符合觀測狀況。 模式經過驗證後，應用於探討不同底泥床通量條件下對水體中銅分佈影響；另外模式亦應用於探討潮週平均鹽分、流速、懸浮泥砂、重金屬銅濃度與重金屬銅傳輸通量之分佈變化。 The Danshuei River system is the largest estuarine system in Taiwan. It consists of three major tributaries: Tahan Stream, Hsintien Stream and Keelung River. The estuary is the primary conduit for the transport of water and material from its drainage basin to the coastal ocean. The ultimate fates of land-derived materials, such as pollutants, depend on the water movement in the estuaries. To predict the fate and transport of materials from land to the ocean requires the knowledge of water movement through this stretch of water body. The heavy metal in the rivers and estuaries mainly includes dissolved and particulated phases .The latter is the heavy metal absorbed on the suspended sediment. In general, the distribution coefficient determines the amount of dissolved and sorbed fractions. In order to understand the physical transport characteristics of heavy metal transports in rivers and estuaries, a vertical (laterally averaged) two-dimensional heavy metal transport model was developed and based on hydrodynamics, salt, and sediment transport models. The model was applied to the Danshuei River estuarine system which is the largest tidal river in Taiwan and to simulate the copper transport including total, dissolved, and sorbed copper concentrations. The upstream boundaries of the computational domain are: Cheng-Ling Bridge (Tahan Stream), Hsiu-Lang Bridge (Hsintien Stream), Wu-Du (Keelung River). The downstream is at the Danshuei River mouth. The comparisons of field measurement and computed tidal elevation, velocity, salinity, suspend sediment concentration show that they are in good agreement. In order to validate the accuracy of the Heavy metal transport model, two field measurements conducted by the National Center for Ocean Research (NCOR) during 2001 to 2002, were adopted for comparison with simulation results. According to pictures from pollutant area and measured data conducted by the Environmental Protection Administration and National Center for Ocean Research, the high copper concentration exhibits near the Hsin-Hai Bridge. The simulated results reveal that point source loading (250 kg/day) should be added near the Hsin-Hai Bridge to match the field data. After the model calibration and verification, the heavy metal transport model was applied to investigate the impacts on copper distribution in the water column under different conditions of sediment bed fluxes. The model was also used to comprehend the tidally averaged salinity distributions, residual current, suspended sediment concentration, copper concentration and fluxes. |
