Process-based modelling of wave induced salt marsh edge erosion

A process-based model for the lateral retreat of a cross-shore transect of salt marsh under wave attack is developed. Several modifications are implemented in the widely used numerical model XBeach: i) the processes involving the mutual interaction between sand and mud; ii) the effect of halophytic vegetation on modifying the near flow field and in increasing the critical shear stress for soil erosion, and iii) the effect of partially reflected waves on the steep profile of the marsh scarp. Furthermore, the bed elevation update algorithm is modified in order to resemble the lateral retreat of the scarp. Numerical simulations of a salt marsh edge subject to continuous wave forcing are run to investigate the effect of different processes and parameters (e.g. soil composition and vegetation characteristics) on the evolution of the system. Preliminary results show a significant dependence of the marsh scarp behaviour on the relative sand-mud composition. The effect of vegetation in mitigating erosive processes nonlinearly decreases when the relative mud fraction is reduced. The model provides important insights into the processes associated with salt marsh edge erosion.