Upscaling sub-grid scale physical processes in benthic boundary layer for sediment transport processes for engineering morphodynamic models

The quantitative prediction of sediment particle motion in aquatic bodies (like rivers, estuaries and coastal areas) by numerical modelling is one of the most challenging problems in geosciences and civil engineering (Amoudry & Souza, 2011). The sources of errors can be separated into: (1) the limitations of the models (due to approximations and computational limits), (2) the lack of sufficient data to initialize and validate the model and for the boundary conditions, (3) the heterogeneous properties of the individual particles and the bed composition, and (4) the poor description of subgrid scale physical processes (like particle-fluid interaction and interparticle collisions). The present research attacks the fourth bottleneck and addresses the improvement of the description of subgrid scale physical processes in benthic boundary layer in morphodynamic numerical model. In order to properly take into account the subgrid scale physical process in the benthic boundary layer, a low-Reynolds k-epsilon turbulence model for particle–laden boundary flows, analytical closures for IBL sediment transport, IBL energy consumption and a low-Reynolds law-of-the-wall, a modified k-epsilon turbulence model for coastal sediment transport applications on coarse vertical resolution, a new, robust friction law for sediment-laden flows in depth-averaged morphodynamic models, proper sink terms for spectral wave models to account for energy dissipation by sediment transport and fluid mud are developed. This work presents the development a new high resolution numerical model for particle transport and the implementation of the proper inclusion of energy consumption by particle transport in suspension flow, in particular by bedload in the inner boundary layer which allows a much more accurate calculation of the hydrodynamics, free surface wave propagation and morphodynamics in environments with erodible beds. These new process models are tested in real case studies and the spatial focus is the Belgian Coast including the Scheldt Estuary.