Numerical Simulation Of General Scour At The Bridge Crossing Downstream Of The Dam

The contraction of natural channel caused by bridges spanning over the river has influences on the bed evolution in a certain range of upstream and downstream of the bridge sites. Furthermore, the conditions of incoming water and sediment from the upstream would change after the operation of the dam and also influence the river bed evolution. According to the basic theory of river dynamics, this thesis first analyzed the basic mode of sediment incipient motion and the formulae of Sediment Carrying Capacity, and then built the one-dimensional general scour mathematical model based on the conception the theory of sediment entrainment rate for the first time, with flow equation and Exner equation.In the model, the influence of the bridge contraction was considered and the smaller spatial step length was adopted in the range during the computation. To validate the model, the observed data of Zhicheng Bridge downstream of the Three Gorge's Dam in Yangtze River was used and the computation results were satisfying. Finally, the comparisons between the computed reaches under the consideration of contraction or not were made properly on the influence of the river bed evolution and the influence of the change of the sediment on the general scour in the downstream was also analyzed and some important results were derived.