Evolution Mechanism of Meandering River Downstream Gigantic Hydraulic Project I: Hydrodynamic Models and Verification

The evolution mechanism of meandering river is one of essential references to predict the evolution disciplines of meandering river. Jingjiang curved reaches are the typical meandering river; more specifically, they are located downstream the gigantic hydraulic project named Three Gorge Project (TGP). Because the incoming water and sediment condition have been changed by the gigantic project, the evolution behavior of Jingjiang curved reaches changes a lot, making the evolution behavior unpredictable. However, traditional two-dimensional (2D) hydrodynamic model could not simulate the transportation characteristics of unbalanced and suspended sediment, leading the predict results of 2D model are far from the measured data. This paper presents a theoretical and numerical approach that explores the evolution mechanism of meandering river downstream gigantic hydraulic project. Firstly, the evolution behavior and evolution disciplines of Jingjiang curved reaches were classified before and after the hydraulic project implement respectively. Secondly, a 2D hydrodynamic model was set up and verified according to the measured data. And then a superior three-dimensional (3D) numerical model, whose boundary conditions were simulated by the results of the 2D numerical model, considering the unbalanced water and sediment transportation properties, was developed and verified by the measured data. Research results show that the 2D model displayed a reasonable accuracy in predicting the water level, branch diversion ratio, and flow velocity; the 3D model displayed a better accuracy in predicting the water lever, vertical flow velocity, longitudinal flow velocity, sediment concentration, and sediment variable quantity. Both 2D and 3D models could be applied to study the evolution mechanism of meandering river; especially the proposed 3D model considering the sediment transport in longitudinal, transverse, and vertical directions will improve the accuracy of behavior prediction and will help decision-making for the river regulation.