This research focuses on one-dimensional and two-dimensional hydro-sedimentary numerical modeling, particularly the coupled modeling of a 1D hydro-sedimentary model with a 2D hydro-sedimentary model in rivers and streams. First, the theoretical basis of the phenomenon is discussed. Then, the RubarBE, Rubar20TS, and the Coupled Model from INRAE-Lyon are described, which are used to perform 1D, 2D simulations, and their coupling, respectively. Explicit numerical schemes are used to handle cases where the riverbed becomes dry or wet without stability issues.
These software tools use the median diameter and grain size range of the sediment in the study of sediment transport, which simplifies the computation. They provide various types of results, such as: maximum water heights or flood limits, longitudinal and transverse evolution of the riverbed, liquid and solid flow rates, flow velocities, and evolution of sediment diameters.

In general, the results from the different models are similar. The coupled model remains stable even in cases of widespread bank overflow or dike failure. For lateral coupling, the coupled model saves computational time compared to a 2D model and provides valuable results regarding flood characteristics and the evolution of the riverbed topography. However, the simplified representation of sediment characteristics in both the 1D and 2D models has revealed discrepancies in the upstream/downstream coupling, which occurs at a cross-sectional section perpendicular to the flow direction. This is because the assumption of homogeneous velocities and concentrations is no longer valid for estimating sediment transport in this case.
The sediment transfer coefficient, recently integrated into the coupled model, works well in lateral coupling, but it remains a very simplified solution. Further research is needed to define an appropriate sediment distribution for the 2D side of the boundary between the two models.

Publication

Mezbache S, Paquier A, Hasbaia M (2020) A coupled 1-D/2-D model for simulating river sediment transport and bed evolution. Journal of Hydroinformatics, 22(5) : 1122-1137. IWA Publishing ; doi : 10.2166/hydro.2020.020