The integration of coastal dunes planted with vegetation and dikes combines traditional infrastructure with dynamic aeolian sediment and ecological processes to enhance coastal resilience. The functioning of such dune-dike hybrid Nature-based Solution strongly depends on aeolian sediment transport and the vertical growth rate of vegetation. We used the AeoLiS numerical model to investigate the relative importance of aeolian and vegetation dynamics in the evolution of a 120 m long and 20 m wide marram grass-planted dune field on a Belgian sandy beach backed by a seawall, constructed in 2021. AeoLiS proved to be a promising tool for predicting these systems, effectively capturing aeolian sediment deposition, vegetation growth, and profile development three years post-construction. Seasonal variations in vegetation trapping efficiency, driven by sediment burial, and seasonal plant growth emerged as important factors controlling dune growth. Profile development discrepancies were attributed to unaccounted biotic and abiotic factors, highlighting the complexity of coastal eco-geomorphological processes. Dunes planted with vegetation wider than 20 m were identified to enhance sediment trapping without an increase in dune height. These findings offer actionable insights for coastal management, promoting strategic dune design and planting approaches to reinforce shoreline resilience. Additionally, the findings underscore the necessity for advancing eco-morphodynamic models and deepening our knowledge of coastal dune dynamics.

A model that simulates surface moisture content on sandy beaches for aeolian transport applications is developed and integrated into the aeolian transport model AeoLiS. The moisture content of a thin surface layer (≈2 mm thickness) is computed as a function of wave runup, precipitation, evaporation, percolation, and capillary rise from the groundwater table. The groundwater table is simulated using a modified Boussinesq equation accounting for the overheight due to wave runup. The surface moisture due to capillary rise is simulated with an experimentally determined soil water retention (SWR) curve of the “van Genuchten” type. Hysteresis is accounted for by differentiating between SWR curves for drying and wetting conditions. The model is tested against a data set of 221 point observations of surface moisture from Noordwijk beach in the Netherlands. The measured surface moisture within the study area displays large spatial and temporal variability. The model results display an expected cross-shore gradient of moisture content, but also a large scatter when compared to the data. The scatter may partly be explained by local variability of hydraulic properties that are not accounted for within the model. Despite the scatter, the proposed surface moisture model is a starting point to integrate the transport limiting effect of surface moisture into meso-scale aeolian transport models. To facilitate model setup and the use of this surface moisture model, the soil water retention data from 10 beaches with variable grain size characteristics are provided in this study. Future studies may focus on additional model validation against data sets with variable meteorological conditions and simultaneous moisture and aeolian transport observations.