This paper reports on the preliminary results from a true-to-scale flume experiment carried out to better understand plant and sediment responses, as well as their interactions, under extreme hydrodynamic forcing in shallow coastal salt and brackish water marsh settings. We report here on bed level changes under individual plant seedlings and denser plant arrangements transplanted from seed and field sites on the Scheldt estuary and on the response of vertically extracted sediment cores from two UK field sites with contrasting sediment characteristics and plant species occupying the surface. Due to the relatively recent completion of the experiment in addition to time-consuming, complex data processing and analysis methods more time is required before definitive quantitative results can be reported. Initial insights into the general behaviour of salt marsh sediments under horizontal and vertical wave-driven hydrodynamic forcing, however, confirm marsh surfaces to be highly stable structures, at least during extreme storm surge events.