水平束縮沖刷是水流在河道中橋台外所造成的河床沖刷行為。本研究利用試驗水槽進行束縮沖刷實驗，將試驗結果與前人公式之推估作比較，找出適當之迴歸式。並探討影響束縮刷深的主要因素，以了解造成底床嚴重刷深之機制，並探討改善束縮沖刷的工法。 就清水沖刷而言，束縮沖刷深度受兩因子影響；一為束縮率，一為平衡水深。當束縮率增加時，束縮刷深所在總刷深的比例會比較多。反之，則局部刷深則佔總刷深的比例較高。不過當沖刷形式為局部沖刷時，束縮率是有限制的影響沖刷深度。 The horizontal contraction scour around the bridge abutment is examined in this study by experimental study. Both short and long contractions are performed in the laboratory, and are compared with available formulae. Experimental results of the contraction scour are helpful to understand the mechanism of bed variation, and to improve the scour countermeasures. The depth of the contraction scour is controlled by two factors, i.e. the contraction ratio and the equilibrium water depth. Increasing the contraction ratio, contraction scour will take high proportion of the total scour depth. On the contrary, the local scour depth will take a large proportion of the total scour depth. Since is mainly due to the local scour, the contraction ratio only affected the depth of the scour slightly.