||海灘在波浪作用下會有不同變化,這主要 是受到漂沙的支配。本文之數值模式係模擬當 波浪來襲時所生之向離岸漂沙對其海灘斷面所 產生的變化情形。模式中分為水理模式和輸沙 模式。 Meyer & Taylor(1972)認為波浪在海灘斜坡上之 溯升及回降可以用淺水波理論來描述,本文以 Hibberd & Peregrine(1979)依淺水波理論所建立之模 式模擬單一波之溯升及回降;而回降情形之模 擬,在理論上有其極限,超過該極限時本文根據 Ho & Meyer(1962)所提出波浪回降時依自由落體方 式回沖的觀點,完成整個海灘斜坡上波浪溯升 及回降的過程。 在輸沙模式中利用Bagnold(1966)總輸沙量 (total load)公式估算整個海灘斜坡上的輸沙和斷 面變化情形。本模式考慮了地形變化及其衍生 之輸沙能力的變化。本文所模擬之入射波為週 期性規則波且海灘之沙質為均勻粒徑,由模擬 結果發現平衡海灘之形成是有可能,文中對此 有一描述與分析。最後分別比較在不同的入射 波波高、海灘坡度、波浪週期、沙質粒徑等不 同情況和輸沙之間的關係並討論沙洲的形成過 程和沙洲尖銳度之變化。
The incident waves on the beach and subsequent uprush and backwash change the beach profile, due to the sedimentation. This study is to develop a numerical model to calculate the onshore-offshore sediment on a sandy beach, which includes hydrodynamic model and sedimentation model. Meyer & Taylor (1972) pointed out that the shallow water wave theory can adequately simulate the wave uprush phenomenon. Using Hibberd & Peregrine(1979)'s numerical model which is based on the shallow water wave theory, this study developed a numerical scheme to simulate the phenomenon of wave uprush & backwash. Owing to the limitation of this wave theory, most of the backwash process can only be modelled by the idea of Ho & Mayer (1962), who have found that the major backwash mechanism was based on the free falling motion. The wave runup on a sloping beach is thus being simulated. As for the sedimentation model, the concept of total load developed by Bagnold (1966) is used. This numerical model has also taken into consideration of the changes of the beach profile. The wave is periodic and the sand grain is uniform. An equilibrium beach can be found by the simulating results. The relation between erosion rate and bar steepness has been studied. The effects of some important parameters on the sedimentation on this sandy beach are also considered.