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Formation and Characteristics of Sandbars at Both Experiment and Prototype Scales

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The large-scale sandbars resulted from the instability of loose sedimentary materials through complex flow phenomena are very common in lowland rivers. These bars, on one hand, make the river highly unstable forming anabranches, influencing bank erosion, etc.; while these are habitats for various species in river ecosystem on the other. Thus the study on their formation processes and their characteristics at natural scale becomes very urgent for better management of river engineering. RIC-Nays, a two-dimensional model for flow and morphology is utilized in this study, where CIP method for convective terms and depth-averaged parabolic eddy viscosity model for turbulence are applied. Formation processes of alternate and multiple bars in experiment scale are examined to verify the simulation results. The results show reasonably good agreement when compared with theoretical and experimental data. It is found that different initial conditions lead to different equilibrium states, and periodic boundary conditions with a small computation domain tend to stabilize multiple bars. The multiple bar patterns as present in the natural rivers are well reproduced in the simulation, where the evolution of bars is apparent with a pool-bar complex with asymmetrical profile in along-stream section and avalanche face on downstream side.
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Alternate Bar; Bar Formation; Multiple Bars; Pool-Bar Complex

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