Author(s): Thomas Wenka; Andreas Schmidt; Thomas Brudy-Zippelius
Linked Author(s): Andreas Schmidt
Keywords: Waterways; River bends; Sediment transport; 2D-/3D modelling
Abstract: The close interaction of geometric, granulometric and fluid mechanical effects and their influence on bed-forming processes in alluvial waterways require the highest possible temporal and spatial resolution approach. Particularly the threedimensional effects of the flow close to construction works and along river bends play a crucial role. It is quite obvious that 3D flow models allow a better prediction of morphological processes, contradicted, however, by the much higher modelling effort, especially regarding practical problems. This conflict led to the investigation of the potential of threedimensional flow modelling to describe morphological processes better than by 2D depth-average models. Further, the study, implementation and application of different shear stress approaches stood in the foreground of a R& D project of which the main results are presented in this paper. Based on well-documented flume tests in meander models of different curvature ratios 2D and 3D simulations have been performed. For the modelling of a practical problem a stretch of a German inland waterway was selected. The“2D sediment transport model Middle Lower Rhine" (Rhine-km 730. 0 to 776. 5) was reduced to the core region of the curve and reverse curve between Rhine-km 739. 0 and Rhine-km 749. 0 and complemented by a 3D model. The comparison of the 2D and 3D models has shown that with a specific parameterization used in the 2D depth-averaged model the effects of the secondary motion can be sufficiently taken into account in regions of curvature. Due to the direct simulation of such effects and a better approach to the in-situ data, however, the higher computation costs of the 3D model can be justified in certain cases. Therefore, both model approaches should in particular be operated in river sections wi th strong bends. In this way, the results of the simpler 2D model can be evaluated and further adjusted to the specifics of the river reach.
Year: 2015