River-bed scour resulted from the contracted river course by the underwater structure of the bridge endangers the safety of bridge foundations. In this study, the proposed one-dimensional numerical model was adopted to simulate the contraction scour based on the St. Venant equations, and the equations of sediment transport and river bed deformation. In this model, the effective area of flow section was obtained by boundary simplification to consider the recirculation upstream and downstream of the bridge site, and the non-uniformity of sediment was treated by individual fractions. The verification of the numerical model at a bridge crossing in Yangtze River shows that the model is capable of predicting water surface elevations and bed elevations, with absolute error less than 0. 1 and 0. 5 m, respectively. Further results reveal that the contraction scour is noticeable during floods while the river bed would have some minor deposition during low discharge after floods. Furthermore, the proper generalization on the recirculation boundary can have a positive role in the computation of contraction scour which not only makes the results closer to the measured value but also gives a better understanding on the temporal evolution of contraction scour at the near zone upstream and downstream of the contracted flow section under the same water and sediment conditions. Finally, the consideration of sediment non-uniformity is also more reasonable than the previous assumption of uniform sediment in the one-dimensional contraction scour model.%桥梁的水下结构压缩河道,造成河床冲刷,危害桥梁基础的安全.根据水、沙运动及河床冲淤变形方程,考虑压缩断面上下游出现回流的特点,通过边界概化处理,获取有效过流断面面积,用泥沙颗粒分组考虑实际河床泥沙颗粒的不均匀性,建立跨河桥梁压缩冲刷的一维数值计算模型.用该模型计算的长江某大桥河段水位及河床高程与实测值的绝对误差分别小于0.1和0.5m,验证了模型的可靠性.应用该模型对桥址河段河床压缩冲刷的研究结果表明,汛期大流量时冲刷明显,而汛后小流量时可能有微淤；在相同水、沙条件下,对回流边界合理的概化处理可使压缩冲刷计算的结果更接近于实测值,并能反映压缩断面上、下游近区的冲刷发展过程；在压缩冲刷计算模型中考虑河床泥沙颗粒的不均匀性,比以往均匀沙假设更合理.
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