離岸堤爲離開陸地且大致平行海岸之工程結構物，原設計構想是想藉此削減波能，使沈積物於堤後堆積，進而保護堤後的海岸。但堤後堆砂之後，往往造成附近海岸作用的變動，使鄰近地區海岸的地形跟著改變。先前離岸堤相關的研究，多著重以物理實驗和數值模擬的方法，探討堤後堆砂的機制或評估淤砂量，對於地形的影響則少有研究。因此本研究以嘉義好美寮之離岸堤群爲例，從不同時間尺度探討離岸堤對鄰近海岸地形的可能影響。結果顯示好美寮最南側的數座離岸堤，堤後成功聚砂，但在最北端離岸堤的北（沿岸流下游方向），則出現海岸線持續後退，內側防風林倒塌的現象。推測此乃因南側堤後堆砂的效果使原來的治岸漂砂受阻，致沿岸流優勢方向下游海岸呈侵蝕現象，產生類似突堤的效應。
Detached breakwaters are enrineering structures that are placed just offshore and aligned approximately parallel to the local shoreline. They are designed to diminish the wave energy and to trap sediment in the sheltered area. Very rare studies had been done on the coastal landform impacts of this man-made structure, thus we chose a series of detached breakwaters at Haomeiliao, Chiayi as a case to examine this issue. The results show that breakwaters at the southern end had trapped sand successfully to form a buffering beach. In contrast, breakwaters at the site just north she of the northern end, severe erosion occurred. Since the prevailing longshore drift at the Haomeiliao shore is from the south to north, the post-breakwater coastal landform changes are similar to the effects made by a groin.
