為了解養灘時漂沙濃度擴散情形，以作為未來工程設計及施工方案選擇之依據，本研究利用潮流與濃度擴散模式針對沙之不同投放位置、數量、時間及粒徑進行模擬。由模擬結果得知，連續投沙時向外海擴散之漂沙濃度將於投沙一天後達到穩定，但離岸距離將隨漲、退潮變化；而沿岸方向則會隨潮流持續擴散一段時間。在相同投沙量下之漂沙濃度範圍，短時間大量投沙將較連續少量投沙之範圍大。

　　在安平商、漁港防波堤間近岸處投沙，其漂沙濃度範圍將隨投沙點與岸邊距離增加而擴大；其次，於停止投沙後漂沙濃度消散速度則離岸越近消散越快；且高漂沙濃度部分幾乎不會越過防坡堤往南。如投放於安平商港南防坡堤側，其漂沙濃度擴散範圍較放在二防坡堤間大，且會因防波堤產生向海擴散之情形。而投沙點離南防波堤越遠，漂沙濃度沿岸擴散範圍愈大，但垂直海岸方向則逐漸呈現定值。另如投入沙粒徑愈小，則漂沙濃度擴散範圍越大，且沉降時間長，故高濃度影響之時間亦較長。在本海域近岸區投放 之沙，停止投沙4天後，中心漂沙濃度均降至1,000 PPM以下。因此在料源不理想時，要減少養灘漂沙擴散需慎選投沙地點，設置阻砂設施如突堤、離岸堤或潛堤及配合海氣象條件方可成功。

　　This study is intended to probe the behaviour of sand dispersion in beach nourishment; the results may be useful for design and construction of marine works. A composite model of tidal current and concentration dispersion is employed to simulate beach nourishment with various placing locations, quantities, times and particle diameters of sand. To point placing case, the study outlines that the sand concentratuon is dispersed forward to offshore becoming stable after 24 hours of continue dumping, but varied with the distance and the difference of ebb or flood current. Nevertheless, the dispersion continues to growth along the long shore direction. If the sand placing quantity was designed to be a constant value, the instant placing disperses to far area than continuous placing.

　　While the sand is dumped in the near-shore area between breakwaters of An-ping Fishing Port and An-ping Commercial Port, the sand concentration could affect wider areas when the placing location gets farther away from the coastal line. Secondly, the closer to the shore the placing location is, the faster the dispersion occurs after sand placing is stopped, and the high sand concentration is bonded within these two breakwaters and will not pass through the southern breakwater line of An-ping Commercial Port even in flood. However, if sand is placed near the outside of southern breakwater of An-ping Commercial Port, wider areas of dispersion would appear and sand concentration would disperse offshore because of the sheltering of the breakwater. Moreover, when the sand placing location gets farther away from the southern breakwater, sand concentration disperses more widely along the long shore direction, but the variation in the cross direction approaches to a constant value. Finally, the particle size also affects dispersion clearly. The finer the sand particle is, the wider the dispersion area is; and high concentration influences longer because the sedimentation of fine sand particles takes a longer time. In this study the medium diameter is taken as 0.25 mm, and the concentration at the center of sand placing area is reduced to 1,000PPM after 4 days of sand placed. It is concluded that the successful design of beach nourishment project depends on the placing location, the coastal facilities such as groins, detached breakwaters and submerged breakwaters as well as sea climate for the shortage of sediments resources.

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