感潮河段之潮位及河床特性─以淡水河下游為例

The topological and tidal characteristics in the downstream reach of Dan-Shui River

林煒傑(Wei-jie Lin)

指導教授 ： 周憲德

國立中央大學/工學院/土木工程學系/碩士(2007年)

摘要

本研究針對淡水河下游之潮位及河床特性進行現場及實驗分析。於近三年底質採樣分析可知淡水河下游之河床質粒徑介於0.009-0.509 mm，淡水河以社子防潮堤到二重輸洪道出口間之河床質最細(<0.02mm)，基隆河之河床質粒徑(介於0.1-0.4mm)較淡水河為粗。由關渡至河口之粒徑漸粗，於河口最粗，往外海方向則粒徑漸減，故河口的區域存在海相沉積的特性。而由河道斷面資料得知淡水河口之水下地形並無沖積扇地貌，然近十年來在河道內呈淤積現象。
傳統潮汐分析主要以調和分析為主，然而此區域潮位資料受到河道影響，亦或是颱風期間，受颱風等因素之作用下，潮位呈非線性運動，因而採用適用於非線性、非穩態性資料之經驗模態分解法(Huang,1998)，並探討調和分析與經驗模態分解法用於分析颱風期間暴潮偏差之差異性。由結果發現，調和分析並不能完整濾出半日潮之能量且受資料長度影響於非閏年無法分析出Sa分潮，雖所產生之誤差值在容許的範圍內，但就暴潮分析的數量級而言，此誤差量會造成很大的影響；而 EMD可有效析出半日潮之能量，因此計算之暴潮偏差量較調和分析小。在分析1997~2005年河口站與土地公鼻站颱風期間之潮位資料中可發現，取3年潮位資料進行調和分析並用於暴潮分析之結果較佳。此外，土地公鼻之暴潮偏差量均較河口站大。
由渠道實驗結果得知流況為駐波，不同位置之水位同步變化。因此流速與水位之相位差不會因為深度不同而改變，亦不受水位升降影響。在任何深度下水位與流速之相位差大約為 (即90度)，與現地(關渡站)量測之水位與流速關係圖相近。

關鍵字

經驗模態分解法 ； 暴潮 ； 淡水河 ； 底床質 ； 河道斷面 ； 潮汐

並列摘要

The topological and tidal characteristics in the downstream reach of Dan-Shui River is explored in this study by employing field measurement, data analysis and the flume experiment. The median particle sizes of sampled bed material at different sites during last three years are within the range of 0.009 and 0.509 mm, while the bed material in Keelung River is coarser (between 0.1-0.4mm) than that of Dan-shui River. According to the topographical contour lines, the Dan-Shui river mouth does not exhibit an alluvial fan for water depth less than 10 meters .
Tidal behaviors in the river course, especially with the impact of approaching typhoons, become non-linear motions when compared with ocean conditions. Thus both the Harmonic analysis and the Empirical Mode Decomposition newly proposed by Huang et al.(1998) are adopted for data analysis of storm surge deviations. The latter one is suitable for non-linear, non-stationary data. The harmonic analysis can not completely filter out energy of the semidiurnal tide and may be unable to analyze the long-period component (Sa) in the non-leap year based on yearly tidal data. On the other hand, the empirical mode decomposition may effectively separate out the energy of semidiurnal tide, therefore the result is better than that of harmonic analysis. A better alternative to run the harmonic analysis is to take a three-year- span period for tidal analysis which results is better than the runs of either one-year or nine-year intervals. The storm surge deviations at the landward station, i.e., Tu-Di-Gong-Bi Station, is bigger than that of the river mouth station, i.e., the He-Kou Station, due to the flood effect.
The standing tidal wave is observed in the flume experiment, i.e., the water level synchronously changes at different locations. The phase lags of the velocity at different water depths and the surface elevation are around 90o. Similar flow characteristics is observed in the field site at Kuan-Du bridge.

並列關鍵字

bed material ； Dan-Shui River ； river topography ； tide ； storm surge ； Empirical Mode Decomposition

參考文獻

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