Morphological instability in restored intertidal flats: How anthropogenic structures drive early‐stage evolution

Coastal wetlands play a crucial role because of their wide range of ecosystem services, including coastal protection, carbon sequestration and biodiversity support. However, these environments are increasingly threatened by land reclamation, sea-level rise and sediment supply reductions, leading to widespread degradation. Managed realignment has emerged as a nature-based solution, allowing tidal processes to restore coastal wetland function. While extensively studied in natural settings, the evolution of restored intertidal flats remains poorly understood. This study examines sediment deposition, vertical accretion and morphological evolution in three human-induced intertidal flats across different tidal environments: Barbamarco Lagoon (microtidal, Italy), Perkpolder (macrotidal, The Netherlands) and Converse (hypertidal, Canada). The analyses followed the same procedure in all environments and were achieved through the use of sediment traps and digital elevation models, integrated with river and tidal records. Results indicate that during the early years of development, managed realignment sites experience rapid accretion in unusual locations of the intertidal flats (e.g. inside channels) and high erosion of artificial structures (e.g. creeks, inlets). This morphological instability influences sediment redistribution and intertidal flat evolution, potentially leading to self-cannibalisation, where erosion of the artificial structures feed the system itself. These findings highlight the importance of long-term monitoring to assess the sustainability of restored intertidal flats and improve predictions of their development. Future research should focus on how coastal wetland design influences long-term evolution and how sediment supply, tidal range and human interventions shape their resilience in the face of climate change.