The braiding intensity and dynamics in large braiding rivers are well known to depend on peak discharges, but the response in braiding and channel–floodplain transformations to changes in discharge regime are poorly known. This modelling study addresses the morphodynamic effects of increasing annual peak discharges in braiding rivers. The study site is a braiding reach of the Upper Yellow River. We estimated the effects on the larger‐scale channel pattern, and on the smaller‐scale bars, channel branches and floodplains. Furthermore, we determined the sensitivity of the channel pattern to model input parameters. The results showed that the dominant effect of a higher peak discharge is the development of chute channels on the floodplains, formed by connecting head‐cut channels and avulsive channels. Widening of the main channel by bank erosion was found to be less dominant. In addition, sedimentation on the bars and floodplains increased with increasing peak discharge. The model results also showed that the modelled channel pattern is especially sensitive to parametrization of the bed slope effect, whereas the effect of median grain size was found to be relatively small. Copyright © 2018 John Wiley & Sons, Ltd.
The performance of three different hydrodynamic modelling packages is compared in this study, namely Delft3D, Delft3D FM (both developed by Deltares) and MIKE 21 FM (developed by DHI). Delft3D and MIKE 21 FM are internationally known software packages while Delft3D FM (formerly known as D-Flow FM) is a relatively new package. The models use structured approaches (Delft3D), unstructured approaches utilising triangular and quadrilateral elements (MIKE 21 FM) and unstructured approaches utilising elements ranging from linear to six sided (Delft3D FM). Models of Western Port, Australia, were developed using the three different packages to allow a comparison of performance and to determine if there are any differences in using structured versus unstructured approaches. Model performance has been assessed based on model calibration, representation of channel flows and computational efficiency. Despite the inherent differences in the grid configuration and the implementation of the numerical schemes between structured and unstructured approaches, both approaches have been shown to be able to accurately predict hydrodynamic conditions in a complex estuarine environment. The unstructured approach was found to be the most computationally efficient both when run on multiple cores (MIKE 21 FM was the most efficient) and when run on a single core (Delft3D FM was the most efficient).
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