工程上常用丁壩來導流及保護河岸，不同方向的丁壩擺設分別有不同用途，其中向下丁壩較少被使用，但以往的研究也甚少提及。因此本研究使用大型動床水槽，透過供給沙及水，探討不同角度的單邊向下丁壩對河道形貌的影響。實驗設計了30度與45度兩種不同角度的丁壩，以交錯排列的方式放入3個及5個丁壩進行實驗。實驗階段之間則利用雷射切葉掃描的方式，再透過Matlab建置出完整地形並加以分析。
從實驗結果顯示不同丁壩角度將會對河道形貌造成不同的影響。從定性的觀察發現，30度丁壩將水流導向對向河岸的能力較強，因此能夠使對向河岸發展出凹岸侵蝕的形貌；45度丁壩的局部沖刷能力較強，形成的沖刷坑會比較靠近壩頭且集中，且能將較多泥沙帶往背風側堆積。與沒有丁壩的原始河道比較後則發現，加入交錯連續向下丁壩會使泥沙較平均地堆積在河道之內。
最後透過定量的分析探討不同丁壩角度對局部堆積及侵蝕總量的影響，分析後發現加沙是造成堆積及侵蝕量差異的主要原因：在加沙的情況下，30度丁壩下游會有較多的堆積量；少了大量泥沙的影響，兩種角度丁壩的局部堆積及侵蝕總量差異不大。

Spur dikes are widely used on flow deflection and bank protection. Different direction of spur dikes will affect engineering applications. However, within the types of spur dikes, less affection has been paid on downward spur dikes. In this study, we use large-scale movable-bed experiment to explore river morphology in response to different angle of downward spur dikes. Successive topographies were scanned to construct high resolution digital elevation models (DEMs).
The results show that different angle of downward spur dikes will affect river morphology. 30 degrees downward spur dikes have stronger ability to deflect flow, then those of 45 degrees. Overall sediment in a channel with downward spur dikes will evenly depositions compares to an alluvial river without spur dikes. Finally, the volume of local deposition and scour in response to difference angle of downward spur dikes were discussed. Implications of downward spur dikes were also suggested in conclusions.

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