Chapter .32: A 3D morphodynamic process-based modelling of a mixed sand/mud coastal environment: the Seine estuary, France.

As in many coastal environments, the bed of the Seine estuary is composed of mud and fine sand (respectively carried from the upstream river and from the sea). Their distributions are related to the hydrodynamic features of the estuary and the sediment bed can be stratified. In order to understand the major morphological behaviours of the estuary, a morphodynamic numerical process-based model is developed starting from a validated fine sediment transport model (Le Hir et al., 2001). The erodibility of the sediment accounts for the proportions of mud and sand; following Van Ledden (2001), two main regimes of erosion are distinguished (a non-cohesive and a cohesive one) using specific formulations to calculate the sediment erosion fluxes. In addition, the sediment column is discretized in thin layers (approximately in mm) and consolidation effects of mixed cohesive-type layers are simulated. Then the erodibility of the superficial layers depends on the relative mud concentration (i.e. between the sand grains). Simulations starting from arbitrary surficial sediment cover show that the model is able to reproduce realistic sediment distributions in the Seine estuary. The main observed morphological trends are qualitatively reproduced by the model, especially concerning the progradation and the rotation of the banks at the mouth. [ABSTRACT FROM AUTHOR]