淡江大橋興建對淡水河口地形變遷之影響研究

Abstract

淡水河為台灣北部地區最大的河川，輸砂量相當可觀，海岸漂砂加上河川輸砂增添海岸地形變遷之複雜性。本研究旨在探討短期颱洪事件下，淡水河口及其近岸地區變化狀況，數值模擬選用丹麥水利試驗所研發之MIKE21模式進行計算，模組則採用流場、波場及漂沙模組。研究選取淡水河歷年來有完整紀錄之最大颱洪事件－2004年艾利颱風做為模擬事件，針對淡江大橋興建前及興建完成兩種狀況進行數值模擬並分析。 研究結果發現淡江大橋興建後於艾利颱風作用下，河道下游及河口段流速相較無興建淡江大橋為快，且懸浮載運行受橋墩影響，會有分流作用，淡水河口處之侵蝕約略增加0.1公尺，台北港南側至林口電廠堤防間變化約略在0.15公尺內，顯示近岸地區流場、波場及地形變化主要以波浪營力為主。

Danshui river is the largest river in northern Taiwan. The coupled actions of coastal sand drift and river sand input render the coastal variation and erosion situation more complicated. The purpose of this study is about the evolution of the river mouth and coastal landform which will change because of typhoon event. In this case, we will use the Danish Hydraulic Institute´s (DHI) model, named Mike-21, to simulate the effects of the wave, current and the tide which cause the sand transport. Aere typhoon occurred in 2004 was selected to simulate the morphologic changes before and after the Danjiang bridge construction to obtain a better understanding of the influence of Danjiang bridge .

From the results of the numerical modeling, the current speed in downstream channel and river mouth are faster after the construction of Danjiang bridge, Moreover, suspended load will diverse due to the existence of bridge piers. There is a maximum of 0.1 meter contraction scour depth near Danjiang bridge pier. The variation of coastal bed variation and erosion situation between north breakwater of Taipei harbor to the levee of Linkou thermal power plant is within a narrow range about 0.15 meter. It can be seen that wave is the dominant force for the morphologic in the nearshore.