中文摘要：

三峡水库蓄水运用后，下游河道来水来沙条件均会发生改变，从而影响河道河势演变过程（包括垂向冲淤变化以及横向调整过程）。为解决长河道因岸滩崩塌引起的河势演变模拟问题，依据水位、流量及输沙量守恒和河床及河岸变形连续等条件，提出虚拟断面连接法构建了考虑岸滩崩塌的二、三维嵌套河势研究数值模型。采用1996年10月～1998年10月沙市至新厂河段实测资料对模型进行了验证，模拟结果与实测结果吻合较好，从而为定量研究水沙条件变化对荆江河道横向调整过程的影响提供了技术支撑。

英文摘要：

The flow and sediment regime downstream of the Three Gorges Reservoir has been changed dramatically after impoundment of the reservoir. The fluvial processes of downstream channel reaches can be affected as a result of the change. In order to simulate the morphological changes in a long river section, a 2-D and 3-D coupled model for turbulent flow and sediment transport as well as bank erosion is developed. A new coupler is proposed for coupling of the 2-D and 3-D models on the basis of mass conservation for flow and sediment transport. The coupled model is tested on a 60 km long section of the middle Yangtze River for the period from October 1996 to October 1998. The result shows that the coupled model simulates well the alluvial channel migration processes, which demonstrates that the cou- pled model is able to provide an effective method to investigating the morphological changes in response to the changes of flow and sediment regime in the Jingjiang segment of the middle Yangtze River.