Unravelling the physical and ecological drivers of the development rate of sediment erosion resistance in tidal marshes

Climate change effects, such as sea-level rise, lead globally to increased flood and erosion risks. Several ecosystems can contribute to nature-based flood and erosion risk mitigation, and tidal marshes are one of these, as they can attenuate waves, reduce shoreline erosion, and accumulate sediment to keep up with sea-level rise. There is therefore an increasing interest in restoring and creating tidal marshes for nature-based flood risk mitigation. However, natural, restored, and created tidal marshes should be erosion resistant to provide flood risk mitigation on the long-term. Although we are increasingly understanding which factors drive erosion resistance in tidal marshes, it remains unknown how long it takes sediment to become erosion resistant in natural, restored, and created tidal marshes, and how far in advance marsh restoration or creation must be started before marshes are needed for flood risk mitigation. This thesis therefore seeks to improve our knowledge on the development rates of erosion resistance and how these are affected by physical and ecological drivers. We found that vegetation species and sediment characteristics are key drivers of the development rate of erosion resistance. Sedimentation rates, drainage, and tidal inundation duration also influence the development rate of erosion resistance. Additionally, we found that the development of erosion resistance can be fast (less than 6 years) under densely growing pioneer vegetation species. It is crucial to assess the conditions at a planned marsh restoration or creation site and the expected development of erosion resistance, and to give the system enough time to develop erosion resistance before it is needed for flood risk mitigation.