A three dimensional CFD model was used to compute the flow, suspended sediment concentrations and the corresponding bed change over time in a natural river reach of 4km length. The river reach is a part of the river Po near Boretto, Italy and its river bed is dominated by alternate bar development. The results of the model are compared to data from a detailed acoustic Doppler and backscattering survey carried out in the years of 2005, 2006 and 2007 of Bologna University, Italy. The CFD model solved the Reynolds-averaged Navier-Stokes (RANS) equations in three dimensions to compute the water flow and was fully coupled with a sediment transport routine to predict the suspended sediment concentrations and the transient bed deformation. The bed level changes were calculated by solving the continuity equation of the sediment concentration at the bed. In addition to the 3D simulation, the same reach was modeled with a 2D hydrodynamic code with a coupled sediment transport routine and an adaption to three dimensional flow characteristics (quasi 3D (Q3D)). The goal of the study was to investigate the 3D and 2D numerical results for a better understanding of fluvial processes at different scales and to identify uncertainties in the results of the long term 2D simulations. The 3D approach uses a universal method for the calculation of the secondary flow that appears to be important in the observed grain size sorting and alternate bars development. The outcome of the study will improves the quality of long term prediction of a 2D simulation, which is important e.g. navigation channel maintenance.

Modelling alluvial channel dynamics in a river reach dominated by alternate bars.

GUERRERO, MASSIMO;LAMBERTI, ALBERTO
2010

Abstract

A three dimensional CFD model was used to compute the flow, suspended sediment concentrations and the corresponding bed change over time in a natural river reach of 4km length. The river reach is a part of the river Po near Boretto, Italy and its river bed is dominated by alternate bar development. The results of the model are compared to data from a detailed acoustic Doppler and backscattering survey carried out in the years of 2005, 2006 and 2007 of Bologna University, Italy. The CFD model solved the Reynolds-averaged Navier-Stokes (RANS) equations in three dimensions to compute the water flow and was fully coupled with a sediment transport routine to predict the suspended sediment concentrations and the transient bed deformation. The bed level changes were calculated by solving the continuity equation of the sediment concentration at the bed. In addition to the 3D simulation, the same reach was modeled with a 2D hydrodynamic code with a coupled sediment transport routine and an adaption to three dimensional flow characteristics (quasi 3D (Q3D)). The goal of the study was to investigate the 3D and 2D numerical results for a better understanding of fluvial processes at different scales and to identify uncertainties in the results of the long term 2D simulations. The 3D approach uses a universal method for the calculation of the secondary flow that appears to be important in the observed grain size sorting and alternate bars development. The outcome of the study will improves the quality of long term prediction of a 2D simulation, which is important e.g. navigation channel maintenance.
Proc. River Flow 2010
1041
1047
Ruether N.; Guerrero M.; A. Lamberti
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11585/100663
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