Coastal regions face increasing pressure from climate change, sea-level rise, and growing coastal populations. This “coastal squeeze” threatens both the systems’ sustainability and their ecosystem services. Coastal changes depend on the distribution of sediment throughout the system, which evolves continuously through complex transport processes. While we can quantify net morphological changes, this alone provides incomplete understanding of coastal evolution as similar morphological states can result from vastly different sediment movement patterns. Coastline perturbations-deviations from straight coastlines ranging from beach cusps to headlands, deltas, and artificial nourishments-exemplify this challenge. Although their diffusive morphological evolution is well understood, we have limited knowledge of the underlying sediment movement patterns driving this change. This study reveals how coastline perturbations alter sediment transport by tracing particles from origin to destination using Lagrangian tracking at the Sand Engine mega-nourishment. Our results demonstrate that perturbations alter both sediment dispersal and accumulation. During initial stages, the longshore dispersal of sediment is strongly restricted by rapid deposition and burial on both sides of the perturbation. A backward-tracing approach reveals that sediment deposition not only originates directly from the protruding part of the coastline, but also from updrift sources. As coastline perturbations diffuse over time, sediment movement patterns gradually converge toward those of an undisturbed coast. At locations with oblique wave incidence this evolution manifests itself with predominant downdrift dispersal and updrift trapping of sediment from adjacent beaches. The successful application of our Lagrangian approach to this multi-year evolution demonstrates the potential of sediment particle tracking for understanding more complex coastal environments. Increased understanding of sediment pathways enhances our ability to predict and communicate coastal response to interventions, supporting more effective management strategies. ... Read more

Coastal systems provide numerous services to communities worldwide, including flood protection, recreational spaces, and biodiversity support. However, these valuable environments face increasing pressure from climate change, sea-level rise, and growing coastal populations. Coastal management aiming to preserve these services is evolving from traditional "grey" towards sandy Nature-based Solutions (NBS). The success of NBS inherently relies on natural processes driving their evolution. NBS typically aim to fulfil multiple objectives, while having lasting impact crossing multiple domains (such as the nearshore, beach and dunes). This increases the need quantitative tools that describe sediment transport and morphodynamic development across the nearshore-dune system.

This dissertation addresses the challenge of modelling coastal evolution across multiple domains through four complementary aims: (A) enabling process-based description of dune development, (B) demonstrating the technical feasibility of coupling numerical models, (C) mapping sediment pathways across the nearshore-dune system, and (D) demonstrating the practical utilisation of these tools for informing NBS design.

To enable the process-based description of coastal dune development in engineering contexts, the existing aeolian transport model AeoLiS is enhanced with landform-shaping processes, including vegetation growth, topographic steering of wind flow, and avalanching. The goal was enabling the simulation of realistic coastal dune evolution at scales relevant to engineering applications. The enhanced model successfully reproduces four distinct dune landforms under real-world conditions. The simulation of barchan dunes closely matched dimensions and migration rates observed in Morocco. Simulated parabolic dunes reproduced migration rates and seasonal dynamics observed in Brazil. The simulation of an embryo dune field captured the seasonality and spatial sheltering effect as observed at De Hors, Netherlands. Finally, the spatial patterns and volumetric changes of excavated foredune notches along the Dutch coast were successfully replicated. Simulating this blowout development on an engineering scale demonstrated the model's practical applicability.

The nearshore and dune domains function as an integrated system, yet they are typically studied separately using different models. To address this limitation, a coupling framework was developed that enables continuous exchange of bed levels, wave heights, and water levels between three process-based models: Delft3D Flexible Mesh, SWAN, and the enhanced AeoLiS model. The framework was applied to the Sand Engine mega-nourishment in the Netherlands, accurately reproducing observed marine-driven longshore erosion (4.1 Mm3) and aeolian deposition patterns. The simulation results enable the quantification of interactions between domains. Aeolian extraction of sediment from the shared sediment budget reduces marine-driven longshore dispersion by 2%. Meanwhile, marine-driven morphodynamics cause variations in foredune growth; up to 24% lower dune growth in sheltered areas and 7% higher growth along accretive beaches in the fifth year. As these morphological deviations accumulate over time, the effect of these cross-domain interactions intensifies over time. This study demonstrates the feasibility of coupling models at scales relevant to coastal management—spanning multiple kilometres over five years.

Understanding coastal evolution requires more than quantifying morphological changes; it demands insight into how sediment moves through the system. To address this need, a Lagrangian particle-tracking approach was developed that accounts for morphodynamic-driven burial. This extends Lagrangian analysis beyond traditional timescales to multi-year periods. Applied to the Sand Engine simulation, the simulated pathways reveal movement patterns impossible to detect through conventional Eulerian approaches. We analysed both the dispersion of nourished sediment and the origin of accumulated sediment at the Sand Engine's flanks. During initial stages, nourished sediment dispersal is severely restricted by rapid burial. The displacement of particles is reduced by an order of magnitude compared to displacement expected along undisturbed coastlines. Sediment accumulation south of the perturbation includes both direct supply from the nourishment (41%) and indirect contributions from updrift sources (59%). As the coastline perturbation diffuses over time, transport patterns gradually transition toward those of an undisturbed coast.
These result enable improved understanding of sediment movement between sources to sinks and thereby the causal relationships that drive coastal change. Rather than indirectly inferring connectivity from Eulerian morphological comparisons, sediment pathways explicitly visualize sediment movement between domains.

The practical utility of the developed tools was demonstrated by examining how specific design choices might influence dune evolution in both large-scale mega-nourishments and smaller beach nourishments. For the Sand Engine, the impact of multiple alternative design considerations on dune growth was explored. The simulations indicated that removing the artificial dune lake would increase dune growth by 42,000 m3 over 10 years, with effects extending 1,200 m alongshore. Reducing coarse sediment content enhanced dune growth by 65%, and lowering the crest elevation increased sediment availability through more frequent mixing. In a smaller-scale application, we explored using certain decisions in nourishment design to steer sediment supply as an abiotic condition for vegetation growth. Incorporating a lagoon in beach nourishment design restricted sediment supply toward the foredune, reducing total dune growth by 62%. Under the assumption that vegetation depends on sediment burial, vegetation growth was limited, maintaining wider blowout entrances. As a result, the simulated amount of backdune deposition was 23% higher for the scenario with lagoon. Particle tracking analysis revealed that the lagoon design more than doubled the contribution from nearshore sediment sources to backdune accumulation. These applications demonstrate how the developed tools can support the design of NBS aiming to achieve objectives across multiple domains.

This dissertation advances our ability to model coastal processes across domain boundaries, connecting the marine and aeolian environments that have traditionally been studied separately. The development from enhanced dune modelling to coupled nearshore-dune frameworks, advanced sediment pathway analysis, and practical design applications creates new possibilities for coastal management. While challenges remain in computational efficiency and process representation, these tools enable coastal engineers and managers to examine how interventions impact evolution across the nearshore-dune system. As coastal regions continue to face increasing pressures, the ability to connect domains in morphodynamic modelling provides a valuable tool for integrated coastal management. ... Read more

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. ... Read more

Traditionally, independent tools have been used to simulate wave- or wind-driven processes to simulate coastal morphology change. Coupled models that cross the land-sea division and integrate these collective processes can increase our knowledge on complex morphodynamic interactions and improve predictions of the foreshore, beach, and dune evolution. In this paper we present the initial development of a coupled modelling framework capable of numerically predicting the integrated development of coastal landforms, including both marine and aeolian processes, by using a generic model coupling approach that leverages the Basic Model Interface. The aim of this tool is to support the interdisciplinary design of Nature-based Solutions on varying spatiotemporal scales. As shown for the Marker Wadden case, the implemented model functionalities allow for the numerical description of the coast in an integrated manner and thus create opportunities for modeling coastal landform of the nearshore, beach, and dune that would not be possible with a discrete model approach. Specifically, by coupling two discrete numerical models, AeoLiS and XBeach, the aeolian and marine interaction resulted in a more realistic behavior of processes in the intertidal area. After coupling, bed levels compared better to the observations compared to the superpositioned results of both separate model components, which showed the added value and potential of coupled modelling. These findings have implications on the ability to predict spatio-temporal integrated coastal development – including these interacting aerodynamic, hydrodynamic, and ecological processes, which are essential in the interdisciplinary design of NbS. ... Read more

In order to improve the current aeolian modeling, a process-based model is developed by implementing biological and physical processes adapted from different existing models. The current version of the model is capable of simulating barchan and parabolic dunes and the initial stage of coastal dune formation: Embryo dunes. Potentially the model can be used to determine the influence of tidal ranges, storm frequencies, armoring, salinity and precipitation on dune building processes. This will result in a greater insight in the general behavior of coastal systems and on the other hand the model can also be used for engineering purposes. ... Read more