中文摘要：

针对长江中游瓦口子至马家咀河段（弯曲分汊河段）的水沙运动特点，给出了二维水沙数学模型尤其是推移质不平衡输沙计算的模式，主要包括推移质不平衡输沙方程、床沙级配方程、河床变形方程；对模型中的几个关键问题提出了处理方法，如非均匀沙起动及输移规律、床面混合层厚度等。利用大量的水流及河床变形资料，率定了模型的一些参数，进行了水面线，流速分布及河床变形的详细验证。在此基础上，根据设计部门提供的进出口水沙边界条件，预测了三峡工程蓄水初期该河段的冲淤过程与分布及航道条件的变化。

英文摘要：

With regard to the motion characteristics of water-sediment between Wakouzi and Majiazui reach （the meandering and bifurcated reach） in the middle reaches of the Yangtze River, the basic principles of the 2D mathematical model for water and bedload are put forward, including the equation for the non-equilibrium bedload transport, the equation for the bed material sorting and the equation for the riverbed deformation, etc. Some key problems are treated by using the following methods： the incipient velocity and the transport law of the non-uniform bedload, the thickness of riverbed＇s mixed layer, etc. Some model＇s parameters are calibrated by mease of a plenty of flow and the riverbed deformation data. The water surface profile, the distribution of flow velocity and the riverbed deformation are verified. Based on this, the present model, according to inlet and outlet flow and sediment conditions provided by the design unit, has been applied to study a typical meandering and bifurcated reach, that is, training of navigation channel between Wakouzi and Majiazui reach in the middle reaches of the Yangtze River. The process, distribution of erosion and deposition and the change of water level and change of navigable conditions of the study reach are predicated during the initial impoundable stage of the Three Gorges Project.