潮汐效應影響沙洲形成機制之研究

A Study of the Sandbar Evolution by Tidal Current Effect

江允智(Yun-Chih Chiang) ； 蕭松山(Sung-Shan Hsiao) ； 方惠民(Hui-Ming Fang) ； 王星宇(Hsing-Yu Wang)

《海洋工程學刊》 13卷3期 (2013/09) Pp. 275-294

https://doi.org/10.6266/JCOE.2013.1303.06

摘要

潮差較大或海岸地形平緩海域，因潮間帶變動範圍較大，漲退潮時之碎波帶位置較不規律，進而影響離岸沙洲之成長與衰退。以往針對沙洲形成之數值模式模擬，並未考量潮汐效應所引起的岸線水深變化。本研究為修正以往採用單一潮位進行水深修正卻忽略潮汐效應的問題，遂使用包括波浪傳遞模式、水理流場模式、漂沙傳輸模式及海岸地形變遷模式所結合之擬三維海岸地形變遷模式，探討在潮汐效應影響下沙洲的形成機制，及避免漂沙量在緩變地形或潮差較大之海域計算時發生預估錯誤。本研究於擬三維海岸地形變遷模式加入潮汐效應影響，並以10天做為重新計算地形條件之間隔時間，除可有效模擬海岸地形變遷情形，並可合理的預估漂沙量與沙洲生成位置。

關鍵字

離岸沙洲 ； 潮汐效應 ； 擬三維海岸地形變遷模式

並列摘要

Sandbar evolution is a key feature of coastal morphodynamics and nearshore hydrodynamics. Hoefel and Elgar (2003) indicated the mechanics of wave-induced sediment transport and sandbar migration: large waves breaking on the sandbars caused offshore mean currents, which maximum near the sandbar crest, will lead sandbars moved offshore; small waves pitching forward on the sandbars made the onshore acceleration skewness of wave orbital velocities, which maximum near the sandbar crest, will lead the sandbar moved onshore. If the sea-level fluctuated significantly, the dynamic behavior of sandbar formation and migration could be different in high and low water-level. In this study, the characteristic sets of morphodynamics in different water-levels were discussed for a meso- to macro-tidal intermediate beach. A morphological quasi-three-dimensional (Q3D) model has been employed. The morphodynamics response of sandbar formation was compared with the results from mean water-level in all tidal period and high/low tide in half tidal period by Q3D models. It is shown that the water-level fluctuations play the important role for meso- to macro-tidal intermediate beach. Numerical simulations of the multi-sandbar formation and migration for YanLiao coastal area were also validated with field observation data. The results put forward the key role of morphodynamics settings and the set of tidal range in governing sandbar dynamic behavior, and provide strong support for suggestions that sandbars cannot be studied in fixed water-level for meso- to macro-tidal intermediate beach.

並列關鍵字

sandbar ； tidal effect ； quasi-three-dimensional morphological model