Scale problems in 3D sediment transport models and suggestions to overcome them

Sediment transport models are helpful tools to study the dispersion of contaminants attached to fine-grained sediments in the marine environment. Currently used 3D sediment transport models still fail to make good quantitative predictions. Several causes can be attributed to the inadequate description of physical processes which occur at the subgrid scale level. Specific attention is given to the modelling of turbulent mixing, particle turbulence interactions and near-bottom boundary layer processes. A procedure for the development of new subgrid scale closures for engineering models applied to problems at geophysical scales of coastal waters and estuaries, based on two-phase flow theory and data generated by Large Eddy Simulation and low-Reynolds RANS models, is described. This leads to a three-layer approach, comprising a supersaturated near-bed layer, a transition layer (under certain conditions) and the fully developed turbulent water column.status: publishe