本研究於旨在探討台灣桃園縣觀音藻礁海岸的獨特粗糙底床對於波浪之衰減特性影響。因藻礁的粗糙底床具有消減波能及保護海岸等作用，但是吾人對此藻礁上的近岸海流及波浪特性仍不是非常了解。因此本研究利用壓力式水位計來量測藻礁區的波浪的水位及位能變化。為了觀測波浪的衰減特性及波浪之能量通率，因此儀器的佈置在與波浪方向平行的一測線上。所測得的水位則採用頻譜分析並配合線性波理論來推求波浪之波高及能量消散率。本研究採用先期之研究成果，運用波高水深比(即碎波指標)之參數來選取無碎波發生之資料，藉以探討主受底床摩擦對波浪之消散特性影響。研究結果顯示在沒有碎波的消散貢獻下，此藻礁的粗糙底床造成的波浪能量耗損大致會略小於珊瑚礁對波浪消散能力。本研究最後推求摩擦係數並與Madsen [1994]的模式加以考量不同粗糙度所計算出的摩擦係數做比較，結果發現在兩種摩擦係數值較接近的情況下，模式所需輸入的粗糙度不符合實際估測的粗糙度，顯示Madsen [1994]的模式在推估此粗糙邊界所造成的能量耗損仍有改善的空間。 This study investigated the characteristics of wave attenuation over a very rough bottom surface of algal reef in Guanyin village, Taoyuan, northwest coast of Taiwan. The rough surface of the reef produces shear drag and hence can reduce the wave energy to provide a function of shoreline protection. However, the characteristics of tidal currents and waves are so far still poorly understood over the algal reef. Therefore, we used the pressure and temperature sensors to measure the displacement of wave surface elevation and the changes of the potential energy. The instruments were deployed in a line parallel to the wave propagation direction to observe the wave attenuation and the wave energy flux. We used the Fourier spectral analysis combining with the linear wave theory to determine the wave height and wave energy dissipation rate. We used the previous experimental results, the index of wave breaking,to refine the non-wave-breaking data to focus on studying the effects of bottom friction. The results showed that the wave dissipation over the algal reef is comparable but a little smaller than that over a coral reef found by Hunag et al (2012). The computed wave dissipation factor was compared with the friction factor computed using Madsen’s [1994] frictional model with considering different physical scales of bottom roughness . The results showed that the friction factor computed using Madsen’s [1994] approaches the observed energy dissipation factor only when we input a roughness length much larger than the real roughness length of the algal reef, suggesting that an improvement of Madsen’s model may be needed to quantify the wave dissipation over the algal reef.
