Understanding the abiotic factors governing salt marsh dynamics is crucial to incorporate such ecosystems in holistic coastal risk management (Bouma et al, 2014). Process-based modelling of these ecosystems can help to gain insight into their response to changing environmental conditions. Therefore, a new process-based approach was applied to model establishment and survival of salt marsh vegetation, bridging the gap between geophysical and ecological models. A salt marsh ecosystem representative for the Western Scheldt Estuary, the Netherlands, which is characterized by semi-diurnal tides, locally generated waves and transport of fine sediments, was simulated starting from a bare mudflat. Salt marsh development is simulated in a Python script based on two concepts: Windows of Opportunity, accounting for seedling establishment (Poppema et al, 2019), and Population Dynamics, describing the growth and decay of established salt marshes (Temmerman et al, 2007). This external script is coupled to a morphodynamic Delft3D Flexible Mesh model through Basic Model Interface (BMI). The model results show that the establishment of pioneer vegetation on bare tidal flats governs the of tidal channels. The rate of seedling establishment affects the geometry of tidal channels, leading to narrow and deep channels aligned with the direction of tidal flow for fast colonizers (e.g. Salicornia europaea; glasswort) and wider, meandering channels for slow colonizers (e.g. Spartina anglica; cordgrass). Moreover, the response of the salt marsh-tidal flat system to changing abiotic conditions (e.g. waves, sediment influx) is assessed, showing that although fast colonizing salt marsh species are less resistant to physical forcing, they can adjust more rapidly to changes in environmental conditions. Concluding, a new process-based approach for biogeomorphological modelling has helped to improve the understanding of salt marsh development under changing environmental conditions, bringing incorporation of these ecosystems into coastal management a step further.@en