Hydrodynamics Of Jingjiang River And Dongting Lake As A Coupled System

Flooding has been a big threaten to the area nearby Jingjiang River and Dongting Lake. The Three Gorges Project (TGP) is expected to improve this situation but it is also expected to bring many other changes to the dynamic properties of Jingjiang River and Dongting Lake as a coupled system. The purpose of this study is investigate the behavior of flood in Jingjiang River and Dongting Lake, as well as its relation with the operation of TGP.A numerical model based on the finite difference solution of Saint-Venant equation for river flows and the shallow water equation for flows in the lake is developed to describe the flood in Jingjiang River and Dongting Lake. Its validity is verified by comparing numerical results with measured data of water level at critical stations during flood season. The model is also shown to be advantageous when comparing with a fully two-dimensional model based on finite volume solution of the shallow water equation.Various operation schemes of TGP for flood control is critically verified. The numerical results indicate that the efficiency of the different operation scheme of TGP depends to a large extent on the type of the flood. That means, the operation scheme of TGP may have to be some flexibility if realtime information on flood from important tributaries flowing into this area.The performance of several important engineering projects planed to improve the flow condition in Dongting Lake, including construction of a floodgate in rivers diversing water from Jingjiang River to Dongting Lake, regulation of Songzi river and Ouchi river, are also evaluated. It is shown that the floodgate of Songzi river can be a measure to redistribute the discharge between the River and the Lake. It will improve the situation of the west Dongting Lake and will not add too more pressure on Jingjiang River under a usual condition. However, the operation of the floodgate must follow the operation of TGP.A three-dimensional numerical model, including the realizable eddy viscosity model for the turbulence, is employed to investigate some important phenomena in the river-lake coupled system. The phenomena include the complex flow characters in successive bend river, the effect of river cutoffs, the three-dimensional flow structure and the sediment diversion ratio of a branch river.