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This paper reports the development of an enhanced two-dimensional (2D) numerical model for the simulation of flow hydrodynamics and mass transport in meandering channels. The hydrodynamic model is based on the solution of the depth-averaged flow continuity and momentum equations where the density of flow varies with the concentration of transported mass. The governing equation for mass transport model is the depth-averaged convection and diffusion equation. The dispersion terms arisen from the integration of the product of the discrepancy between the mean and the actual vertical velocity distribution were included in the momentum equations to take into account the effect of secondary current. Two laboratory experimental cases, flow in mildly and sharply curved channels, were selected to test the hydrodynamic model. The comparison of the simulated velocity and water surface elevation with the measurements indicated that the inclusion of the dispersion terms has improved the simulation results. A laboratory experiment study of dye spreading in a sine-generated channel, in which dye was released at the inner bank, centerline, and outer bank, respectively, was chosen to verify the mass transport model. The simulated concentration field indicated that the Schmidt number can be used as a calibration parameter when dispersion is computed using a 2D approach with a simplified turbulence model.

Bank erosion consists of two processes: basal erosion due to fluvial hydraulic force and bank failure under the influence of gravity. Because bank resistance force varies with the degree of saturation of bank material, the probability of bank failure is the probability of the driving force of bank failure being greater than the bank resistance force. The degree of saturation of bank material increases with river stage; therefore, the frequency of bank failure is correlated to the frequency of flooding. Consequently, the rate of bank erosion is due to both basal erosion and bank failure, and bank failure is a probabilistic phenomenon. In this paper, for cohesive bank material experiencing planar bank failure, a deterministic approach was adopted for basal erosion analysis, whereas the probability of bank failure was included in the analysis of bank failure. A method for calculating the rate of bank erosion was derived that integrates both basal erosion and bank failure processes, and accounts for the effects of hydraulic force, bank geometry, bank material properties, and probability of bank failure.

The inception of channel meandering is the result of the complex interaction between flow, bed sediment, and bank material. A depth-averaged two-dimensional hydrodynamic model is developed to simulate the inception and development of channel meandering processes. The sediment transport model calculates both bedload and suspended load assuming equilibrium sediment transport. Bank erosion consists of two interactive processes: basal erosion and bank failure. Basal erosion is calculated from a newly derived equation for the entrainment of sediment particles by hydrodynamic forces. The mass conservation equation, where basal erosion and bank failure are considered source terms, was solved to obtain the rate of bank erosion. The parallel bank failure model was tested with the laboratory experiments of Friedkin on the initiation and evolution processes of non-cohesive meandering channels. The model replicates the downstream translation and lateral extension of meandering loops reasonably well. Plots of meandering planforms illustrate the evolution of sand bars and redistribution of flow momentum in meandering channels. This numerical modelling study demonstrates the potential of depth-integrated two-dimensional models for the simulation of meandering processes. Copyright channels (Nicholas and Smith, 1999). Mosselman (1998) added a bank erosion model to a two-dimensional, depthaveraged model and applied it to the Ohre River, a meandering gravel-bed river in the former state of Czechoslovakia.Poor agreement between modelling results and observations were ascribed to the shortcomings of the flow model rather than to the bank erosion subroutines. Duan et al. (2001) solved the two-dimensional, depth-averaged momentum and continuity equations expressed in Cartesian coordinates for the flow field. The secondary flow-correction term (Engelund, 1974) was then implemented to redirect the transport of bedload sediment from the calculated depth-averaged velocity. A new bank erosion model derived from the mass conservation law for near-bank cells was employed to simulate the migration of bank lines. The simulated initiation, migration and evolution of a meander indicated that the rate of bank erosion is a function of longitudinal gradient in sediment transport, strength of secondary flow, and mass wasting from bank erosion. Although sediment transport and basal bank erosion were considered, the geotechnical bank failure of cohesive bank material following basal erosion was neglected . As a result, the simulated meandering wavelength and amplitude did not agree with the observations described in Friedkin (1945). replaced the bank erosion subroutine within the two-dimensional, depth-averaged numerical model RIPA with a new physically based bank erosion model. Within this algorithm, basal erosion of cohesive bank material and subsequent bank failure as well as transport and deposition of eroded bank material were simulated to predict the evolution of meandering channels. The rate of basal erosion of cohesive material was o...

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