中文摘要：

以某铁路涉河大桥为例，根据实测河道水下地形资料进行网格概化，以河网一维数学模型计算成果作为控制边界条件，利用MIKE21建立了平面二维水流数学模型，对涉河大桥桥址河段流场变化进行分析．结果表明，遭遇50年一遇洪水时，桥墩附近的水流流向发生了改变，流速明显增大，会对河道堤防和河床产生冲刷．该方法可在涉河大桥二维水流数值模拟分析中推广应用．

英文摘要：

To study the change of velocity field of fiver-crossing bridge, one fiver-crossing railway bridge was taken as an exam- ple and MIKE21 planar 2-D mathematical flow model was set up, according to the regularization gird represented the actual fiver bed and boundary condition based on the calculation results of one-dimension mathematical model of the whole fiver network. The results show that for the 50-year return period flood, it is the changed flow direction and the clearly increased flow velocity near the bridge piers that scoured the fiver embankment and bed. The method could be used popularly to other numerical simulation on planar 2-D of fiver-crossing bridge.