本研究旨在探討台灣西北部海域，桃園縣觀音鄉藻礁海岸的波浪物理特性。波浪從外海行進至近岸的過程中，波浪能量會因為波浪破碎及粗糙底床地形造成的摩擦阻力使得波浪能量產生衰減。為瞭解此物理機制，本研究於現場的實驗區域佈放壓力式水位儀、聲波式杜普勒流速儀（ADVO）、超音波風速儀及攝影機等，藉此量測藻礁區波浪的水位變化、三維流速、三維風速及紀錄水面有無碎波發生的情形。將量測的波浪水位資料進行頻譜分析，並配合線性波理論，來推求波浪波高及能量消散率。本研究利用所記錄的影像來判別藻礁區波浪碎波的程度，計算碎波指標，並與前人的研究成果作一比較。我們利用此碎波指標將有無碎波影響的物理資料做一區分，並探討其碎波產生的能量消散的貢獻。在有碎波影響的情況下，利用頻譜檢視不同成分波浪的消散程度，發現能量耗損主要集中在入射波主頻附近的成分波浪。另外，在沒有碎波影響的情形下，假設底床消散為波浪耗損的主要貢獻，將所得的波浪能量耗損率利用底床流速的三次方參數化迴歸出摩擦係數，其結果約略小於珊瑚礁的摩擦係數，並和Hsu [2013]的研究成果相似。本研究為比較在底床摩擦主導波浪消散下之係數，利用Madsen [1994]邊界層理論的模式Sedtrans05輸入不同粗糙度算出的摩擦係數與實驗數據進行比較，結果在摩擦係數接近下所輸入的粗糙度與現場的粗糙度有所差異。最後分別利用Thornton and Guza [1983]和Battjes and Janssen [1978] 的半經驗模式估算碎波能量消散，與實驗數據比較後發現模式會有高估的現象。;This study aims to investigate the characteristics of wave attenuation over an algal reef, Guanyin village, Taoyuan, northwest coast of Taiwan. When ocean waves propagate from offshore into nearshore regions, the wave energy is reduced due to wave-breaking and bottom friction. In order to understand the physical mechanism of wave attenuation, we used acoustic Doppler velocimeter(ADV), ultrasonic Anemometer and camera to measure the displacement of water surface elevation, 3-D fluid velocity, 3-D wind velocity, and surface signatures due to wave-breaking in the field. The wave height and wave energy dissipation was determined from measured surface elevation data by using the Fourier spectral analysis combining with the linear wave theory. We used camera to record the water surface to determine the wave-breaking index and then to compare with the results reported by previous studies. The data were separated into two groups to separate the effects due to wave-breaking and bottom friction. For the wave-breaking case, we found that the wave energy is mainly dissipated near the dominant wave frequency of the incident waves. In addition, for the non-breaking case, the bottom friction is assumed the major contribution of wave dissipation; we compute the near-bottom velocity and use cubic regression to obtain the friction coefficient. The coefficient is found to be smaller than the recently reported value over coral reefs but is comparable to that over an algal reef found by Hsu [2013]. Two semiempirical models are used to estimate wave-breaking dissipation rate, including of Battjes and Janssen [1978]and Thornton and Guza [1983], and the results show that wave-breaking dissipation rates predicted by the two models are higher than experimental results.
