Numerical modelling of heterogeneous sediment transport: new insights for particulate radionuclide transport and deposition

A sediment transport module which solves simultaneously bedload and suspended load is developed, in a context of multiclass sediment transport. Different approaches are used to simulate each transport mode: (i) bedload transport results from divergence of transport capacity and (ii) suspension transport is solved using erosion and settling fluxes associated with advection/diffusion equation. A focus is made on the significance of hiding and exposure processes in case of heterogeneous sediment bed. Their influence is strong on bedload sediment transport, and induces specific trends of sediment sorting in sand dunes. The application to heterogeneous sediment dynamics in the macrotidal area of the Normand Breton Gulf (English Channel), show that hiding and exposure processes enhance the trapping of fine sediments (p articles 64 μm, on which radionuclides are likely to adsorb) in locations where coarsest sediments are dominant.