Author(s): Guohong Duan; Yafei Jia; Sam S. Y. Wang
Linked Author(s):
Keywords: Numerical Model; Meandering Channel; Bank Erosion; Sediment Transport; Alluvial Process; Meandering Migration; Sedimentation; Two-dimensional Model; Depth-averaged Model
Abstract: Meandering channels are characterized by their shapes that consist of a sequence of smooth bend loops. A remarkable property of meandering evolution processes is the persistent erosion along the outer bank and sediment deposition along the inner bank, which form the unique alternate bar and pool topography, and make a meandering channel migrate downstream. Because of the complexity of the phenomena and the variability of boundary conditions, the prediction of meandering channel processes by laboratory experiments, field data analysis, and theoretical analysis can only describe the channel centerline' s statistical tendencies with the averaged mean properties of bend geometry and flow conditions. With the advancement of high-speed computers, the simulation of meandering channel evolution processes with a numerical model becomes feasible and costeffective tool. In this paper, a meandering channel migration model is presented in which flow, sediment transport and bank erosion are computed. As has been recognized by many researchers, bed load transport in the transversal direction due to both the secondary flow and the transversal component of gravitational force is appreciable in addition to the transport in the longitudinal direction. An enhanced twodimensional depth-averaged model called the enhanced CCHE2D (Duan, 1998), in which the characteristics of the secondary flow formulated from a three-dimensional model, CCHE3D, have been applied to convert the two-dimensional flow field to a three-dimensional one, is used to simulate the flow field. Therefore this enhanced 2D model is capable of simulating the bed morphological change under various boundary conditions. Suspended sediment transport rate is obtained by using this quasi-3D velocity field. Upon knowing the sediment transport rate, sediment continuity equation is solved to obtain bed elevation change. Instead of using Ikeda’s (1981) bank erosion method, a bank erosion rate equation in the partial differential form is derived based on the conservation of momentum and mass at near bank region. The speed of bank retreat or advance is related with the gradient of longitudinal sediment flux, the strength of the secondary flow and the amount of sediment eroded from the bank. Finally, this model is verified by predicting the developing processes of a meandering channel. The downstream migration, lateral growth, distortion, and cutoff are simulated by this model. The model can be used as an alternative tool for hydraulic engineers to predict the evolution processes of a meandering channel.
Year: 1999