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粗糙海堤面對堤趾沖刷之影響
Effect on Surface Roughness to Toe Scouring of a Slope Seawall
摘要
當波浪作用於海堤時，在堤面上發生溯升現象後，水體沿堤面廻流下刷，再與入射之波浪產生交互作用，此一繁雜之機構常導致提趾冲刷。本研究係以動床模型試驗方式，探討堤面粗糙度對下刷水流强度與提趾冲刷深度之影響。經由實驗結果發現，粗糙堤面可適度削減堤面下刷水流强度、波浪反射率及溯升高度；而原先光滑堤面堤前冲刷劇烈之L型冲刷，堤面披覆粗糙物後能使其堤前之最終冲刷深度及堤前冲刷坑距離減小；而原先屬於N型之冲刷型態，其外海波浪節點處的冲刷深度則有隨著粗糙度提高而減少之趨勢。此外，本研究由堤趾處水流强度之能譜分析可得，當堤面披覆粗糙物後，堤趾處水流能譜主頻上之能量强度相較於光滑面有很明顯的減弱，而各粗糙面之間，其主頻上之能測强度則沒有顯著之差距。由於非線性之效應，入射波浪與下刷水流交互作用時，水流能譜會產生次主頻之能量。原先屬於L型之沖刷型態當主頻上之能量受粗糙度之削減而變小，若其次主頻之能量又能與主頻相差不遠時，則其底床冲刷型態會有變成N型之趨勢。
並列摘要
The variation of the toe scours profile by the surface roughness of a slope seawall was investigated experimentally in this research. The effects of the roughness on the wave characteristics, including the wave run-up on the slope, the flow in the down-rushing wave and the wave reflection from the wall, are also explored. Two main types of the toe scours, named the L-type and N-type, were performed in the experiments. It was found from the experiments that the surface roughness was potentially reducing the intensity of the down-rushings flow and the wave run-up height, even the reflection of wave. The maximum depth of te scours as well as the scouring distance was thus reduced in the light of the surface roughness. The scouring depth and the values of the wave characteristics on the slope were descended obviously due to the surface roughness, from comparing with the smooth surface. However, these descended values were limitedly increased as the surface roughness increased.