Numerical Simulation of Erosion Processes on Crossbar Block Ramps

Mario Oertel, Daniel B. Bung, Jan Balmes

Tuesday 30 june 2015

14:20 - 14:35h at Mississippi (level 1)

Themes: (T) Sediment management and morphodynamics, (ST) Sediment transport mechanisms and modelling

Parallel session: 6A. Sediment - Erosion

Crossbar block ramps are nature-like flow structures to conquer large river bottom steps with adequate flow velocities and flow depths for fish passage. Therefore, the channel will be divided into several basins, formed by crossbars of large stones. Within these basins, a bed material layer is placed to avoid erosion processes and hence to reduce the risk of structural failure. To guarantee stable block ramps, an adequate design is essential. Therefore, erosion processes within the basins must be analyzed to develop design formulas for practical engineers. In the main focus of interest is the material diameter, and density, to avoid relevant movement, which can decrease the stability of the structure. Nowadays, numerical simulation tools revolutionize the hydraulic engineering field and flow simulations in 1D and 2D are state-of-the-art. But sediment transport simulations are still imprecise and difficult to adopt. For 2D transport processes in plan view (depth averaged), numerical 2D simulation products can be used. Therefore, a detailed calibration with field data is necessary, to ensure correct results. For detailed sediment transport and erosion studies, e. g. in the near-field of hydraulic structures, 2D sectional models or 3D models are necessary. In this context the present paper deals with a numerical model of a crossbar block ramp. The code FLOW-3D is used to include a packed sediment fraction within the model. For various flow regimes the movement of base layer material between the crossbars is analyzed in detail. Numerical model results are compared with experimental model results from a scaled physical model. The aim of the study is to focus on the comparability between the experimental and numerical model relating scouring processes.