河口為銜接河川與海洋的交界處，受波浪、潮流、河川流量、不規則地形等因素，及其交互作用所影響，導致河口輸砂及沿岸漂砂行為十分複雜，海岸鄰近河口處造成的地形變遷也較難以模擬及預測。河川來源沉積物被河水帶出河口時，受潮汐作用而影響輸砂運動方向，河水與海水鹽度及密度不同，二水體在河口處交會時，河海水的混合或分層的情形會影響沉積物在河口處的隨海流漂移或滯留等情況。本研究透過電腦數值模式Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST)，模擬雲林海域在河川與潮汐作用下，濁水溪口沿岸的輸砂情形；颱洪期模擬結果顯示，在河川洪峰流量及高泥沙濃度抵達河口，於潮汐週期作用的情況下，泥沙在漲潮時往東北方傳輸，在退潮時往西南方傳輸，颱風通過後大部分泥沙仍存於水體中，隨潮汐週期性運移，淤沙分布於河道及河口沿岸處。由基流期模擬結果顯示，河川基流期之餘流場 (Residual Flow)所顯示的優勢流向，與中央大學太空及遙測中心所研究之歷年沙洲動向相同，由東北往西南方向前進。在潮汐作用且無額外沙源供給的情境下，其地貌變遷之模擬結果顯示，於雲林沿海的三條崙沙洲以及箔子寮沙洲，面積逐漸減小且隨著時間推演有逐漸陸化之趨勢。

Estuaries are the junction between rivers and oceans, hydrodynamics are affected by waves, tides, river discharge, irregular topography, and other factors and their interaction, resulting in very complex coastal sediment transport and drifting behavior in estuaries, and the morphological changes from the estuary to nearshore are difficult to predict. When riverine sediments are carried out of the estuary by river flow, the direction of sediment transport is influenced by tidal effect, different salinity, and density distribution of water column in the estuary. COAWST(Coupled-Ocean-Atmosphere-Wave-Sediment Transport), was used to simulate the sediment transport along with the Zhuoshui river mouth in the Yunlin coast under the river discharge and tidal flow. After the passage of the typhoon, most of the suspended sediment is still a presence in the water column, with the movement caused by tidal flow, and the other sediment is deposit along the river channel and the estuary. The simulation result of the low water period shows that the dominant flow direction is from northeast to southwest, which is the same as that of the sandbar movement in the past years studied by the Center for Space and Remote Sensing Research of National Central University. Under the tidal effect and without additional sediment supply, the model results of the morphological changes show that the area of San-Tiau-Luen and Po-Tzu-Liao sandbars along Yunlin coast is gradually decreasing and moving landward.

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