The natural functions of coastal dune systems are under threat. Rising sea level, changing wave and wind climate and increasing human activities in coastal areas lead to ‘coastal squeeze’. An option to mitigate the effects of coastal squeeze can be creating seaward space through artificial beach widening. The Zandmotor mega nourishment placed in 2011 near The Hague (The Netherlands) is used as an example of creating new coastal space. Morphological changes at the Zandmotor have been studied extensively. The sedimentation-vegetation dynamics and its influence on long-term dune landscape development remain underexplored. Here we show that the presence of vegetation has contributed significantly to the increase in dune volume on the Zandmotor landscape. We used publicly available remote sensing data: elevation maps and aerial images. We found only sedimentation in the dune area on a bi-annual scale indicating that wind does not cause erosion at this timescale. Furthermore, we found that the vegetation cover is increasing over time and is often growing around the peaks of the elevation profile. Also, vegetation often stays at/around the same location and multiplies. The presence and growth of vegetation contribute to a significant increase in dune growth, reaching up to 53 m³/m/year. Our results demonstrate that the presence of vegetation has contributed significantly to the increase in dune volume on the Zandmotor landscape. The insights about sedimentation-vegetation dynamics and its influence on dune growth, gained at the Zandmotor, may inform the development of strategies to mitigate coastal squeeze, enhance dune resilience and adapt to the challenges of climate change and human activities.

Coastal dunes form valuable ecosystems that provide flood protection, drinking water, and high biodiversity worldwide. Although their functioning hinges on habitat zonation along >km-scale sea-to-land gradients, infrastructure development progressively squeezes natural dune ecosystems into a narrow strip. Yet it remains unknown how much undisturbed coastal width is required to support the diverse suites of habitats and species assemblages found in natural dune systems. Here, we investigate plant and habitat diversity in 614 plots along 47 sea-to-land transects in the southeastern USA and the Netherlands. We discover a linear relation between habitat diversity and species richness, indicating that species-rich dunes require diverse habitat assemblages. Moreover, we find that both plant and habitat diversity nonlinearly depend on coastal width, with cumulative plant diversity reaching ∼75% of its potential at 800 and 1,800 m widths in the southeastern USA and the Netherlands, respectively. Alarmingly, dune areas are narrower than these widths along 79% and 66% of southeastern USA and Dutch coastlines, highlighting that lack of space compromises biodiversity along the majority of coastlines. Finally, analyses of management measures along the transects reveal that strategic interventions can, at least in part, mitigate biodiversity losses from infrastructure encroachment. As coastal squeeze-i.e., combined losses from infrastructure and sea level rise-is a global phenomenon, our results suggest that it threatens biodiversity in dune ecosystems worldwide. We argue that the establishment or expansion of nature reserves may be vital for conserving wide dune systems and that targeted management measures can help maintain biodiversity where squeeze cannot be alleviated.

Globally, along sandy coastlines, foredunes support ecosystem services including provision of habitat and protection of communities from waves and storm surge. In this Review, we discuss the interactions between sand transport and vegetation processes (ecomorphodynamics) that give rise to the foredune-building feedback as illuminated by empirical and modelling studies. Foredune shape and alongshore continuity depend primarily on sand supply, vegetation density and growth form. For instance, low-lying, creeping herbaceous species tend to form short embryo dunes, whereas tall, dense grasses that grow vertically tend to form tall, narrow foredunes. Climate and weather events, herbivory and anthropogenic disturbances of varying scale affect the foredune-building feedback. For example, small local scale disturbances, such as herbivory or trampling, cause local vegetation loss and erosion. Management activities, such as beach nourishment, can increase foredune sand supply, leading to foredune rebuilding, although the presence of infrastructure on the back beach can inhibit foredune development. At a regional scale, hurricanes and tropical storms cause substantial dune erosion and overwash, potentially resetting the foredune-building process. Sea-level rise exacerbates the effects of storms, leading to increased erosion, saltwater intrusion and a potential landward shift in foredune location. Future research should prioritize integrated ecomorphodynamic observations and modelling to fill critical knowledge gaps and address the effects of changing climate on the foredune-building process.

High-resolution wave measurements at intermediate water depth are required to improve coastal impact modeling. Specifically, such data sets are desired to calibrate and validate models, and broaden the insight on the boundary conditions that force models. Here, we present a wave data set collected in the North Sea at three stations in intermediate water depth (6–14 m) during the 2021/2022 storm season as part of the RealDune/REFLEX experiments. Continuous measurements of synchronized surface elevation, velocity and pressure were recorded at 2–4 Hz by Acoustic Doppler Profilers and an Acoustic Doppler Velocimeter for a 5-month duration. Time series were quality-controlled, directional-frequency energy spectra were calculated and common bulk parameters were derived. Measured wave conditions vary from calm to energetic with 0.1–5.0 m sea-swell wave height, 5–16 s mean wave period and W-NNW direction. Nine storms, i.e., wave height beyond 2.5 m for at least six hours, were recorded including the triple storms Dudley, Eunice and Franklin. This unique data set can be used to investigate wave transformation, wave nonlinearity and wave directionality for higher and lower frequencies (e.g., sea-swell and infragravity waves) to compare with theoretical and empirical descriptions. Furthermore, the data can serve to force, calibrate and validate models during storm conditions. Dataset: https://doi.org/10.4121/233f11ff-7804-4777-8b32-92c4606e56d8 Dataset License: CC-BY 4.0.

Sandy beach-dune systems make up a large part of coastal areas world wide. Their function as an eco-system as well as a protective barrier for human and natural habitat is under increased threat due to climate change. A thorough understanding of change processes at the sediment surface is essential to facilitate prediction of future development and management strategies to maintain their function. Especially slow and small scale processes happening over several days up to weeks at cm level, such as aeolian sand transport are difficult to identify and analyse. Permanent laser scanning (PLS) is a useful tool in the study and analysis of coastal processes as it captures a data representation of the evolution of the sediment surface over extended periods of time (up to several years) with high detail (at cm-dm level). The PLS data set considered for this study, consists of hourly acquired 3D point clouds representing the surface evolution of a section of the Dutch coast during three years. However, it is challenging to extract concrete information on specific change processes from the large and complex PLS data set. We use multiple hypothesis testing in order to reduce the PLS data set to a so-called inventory of trends, consisting of 12.8 million partial time series with associated rate of change and elevation. The inventory of trends proofs to be a suitable tool to identify natural processes such as storms and aeolian sand transport in our test area in the aeolian zone of a sandy beach-dune system on the Dutch coast. We identify these processes and provide a tool to derive summarising data from the complex PLS data set. We find that all partial time series identified as most likely representing aeolian sand transport, result in 1354 m³ of sand deposition in our study area over the course of three years. We also show a comparison with transects from JarKus data and find a correlation between anthropogenic activities and erosion in our test area with a correlation coefficient of 0.3.

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.

Quantitative predictions of marine and aeolian sediment transport in the nearshore–beach–dune system are important for designing Nature-Based Solutions (NBS) in coastal environments. To quantify the impact of the marine-aeolian interactions on shaping NBS, we present a framework coupling three existing process-based models: Delft3D Flexible Mesh, SWAN and AeoLiS. This framework facilitates the continuous exchange of bed levels, water levels and wave properties between numerical models focussing on the aeolian and marine domain. The coupled model is used to simulate the morphodynamic evolution of the Sand Engine mega-nourishment. Results display good agreement with the observed aeolian and marine volumetric developments, showing similar marine-driven erosion from the main peninsula and aeolian-driven infilling of the dune lake. To estimate the magnitude of the interactions between aeolian and marine processes, a comparison between the simulated morphological development by the coupled and stand-alone models was made. This comparison shows that aeolian sediment transport to the foredune, i.e. 214,000 m³ over 5 years, extracts sediment from the marine domain. As a result, the alongshore redistribution of sediment from the main peninsula by marine-driven processes decreased by 70,000 m³, representing 1.7% of the total marine-driven dispersion. From the aeolian perspective, marine-driven deposition and erosion reshape the cross-shore profile, controlling the supply-limited aeolian sediment transport and the magnitude of sediment deposition in the foredunes. In the region with persistent accretion along the Sand Engine's southern flank, a higher than average foredune deposition was predicted due to morphological development of the region where sediment is picked up by aeolian transport. Including these marine processes in the coupled model resulted in an increase of 1.3% in foredune growth in year 1 and up to 6.7% in year 5 along this accretive section. At the northern flank, where the developing lagoon and tidal channel provided increased shelter to the supratidal beach, predicted foredune deposition reduced up to −11.5% over the evaluation period. Our findings show that both aeolian and marine transports impact reshaping the nourished sand, where developments in one domain affect the other. The study findings echo that the interplay between aeolian- and marine-driven morphodynamics could play a relevant role when predicting sandy NBS.

The formation and evolution of coastal dunes result from a complex interplay of eco-morphodynamic processes. State-of-the-art models can simulate aeolian transports and morphological dune evolution under certain conditions. However, a model combining these processes for coastal engineering applications was not yet available. This study aims to develop a predictive tool for dune development to inform coastal management decisions and interventions. The aeolian sediment transport model AeoLiS is extended with functionalities that allow for simulations of coastal landforms. The added functionalities include the effect of topographic steering on wind shear, avalanching of steep slopes and vegetation processes in the form of growth and wind shear reduction. The model is validated by simulating four distinct coastal landforms; barchan-, parabolic-, embryo dunes and blowouts. Simulations, based on real-world conditions, replicate the landform formation, migration rates and seasonal variability.

A beach in Mariakerke-Bad (Belgium) was monitored in 2017-2018 for more than a year with a near-continuous laser scan system. From a total of 8500 scans 7700 hourly scan epochs were used to study the spatio-temporal shoreward sand transport at the beach. In order to account for weather influences and other possible disturbances of the scan-system, a time-dependent correction method was applied to reduce rotation errors up to 0.2 degrees in the point cloud orientation (around the zero point of the laser scanner) reducing height errors on the beach to the order of centimeters. Cross shore analysis of the beach profile shows that shoreward transport occurs at most times during the year with an accumulated maximum of 17m3/m throughout the measurement period and maximum transport rates of 0.6 m3/m/day. However most of the shoreward sand transport is redistributed seawards again due to beach shaping leaving a total of about 2 m3/m a year which is below the average values found along the Belgium coast. The spatiotemporal behavior of the shoreward sand transport has been studied with the 4D-OBC analysis technique which identified accumulations of sand in the full 4D point cloud dataset. A total of about 3600 4D-OBC accumulation events were identified and most found accumulations on the beach can be associated with natural (aeolian) processes. Also, accumulations appear to occur during the whole year which is consistent with the previous cross-shore analysis.

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.

Grain size affects the rates of aeolian sediment transport on beaches. Sediment in coastal environments typically consists of multiple grain-size fractions and exhibits spatiotemporal variations. Still, conceptual and numerical aeolian transport models are simplified and often only include a single fraction that is constant over the model domain. It is unclear to what extent this simplification is valid and if the inclusion of multi-fraction transport and spatial grain-size variations affects aeolian sediment transport simulations and predictions of coastal dune development. This study applies the numerical aeolian sediment transport model AeoLiS to compare single-fraction to multi-fraction approaches for a range of grain-size distributions and spatial grain-size scenarios. The results show that on timescales of days to years, single-fraction simulations with the median grain size, D₅₀, often give similar results to multi-fraction simulations, provided the wind is able to mobilize all fractions within that time frame. On these timescales, vertical variability in grain size has a limited effect on total transport rates, but it does influence the simulation results on minute timescales. Horizontal grain-size variability influences both the total transport rates and the downwind bed grain-size composition. The results provide new insights into the influence of beach sediment composition and spatial variability on total transport rates toward the dunes. The findings of this study can guide the implementation of grain-size variability in numerical aeolian sediment transport models.