S. Faraji Gargari ¹*, S. de Vries² , D. Karssenberg ¹, G. Ruessink ¹

¹ Utrecht University, Netherlands; ² Delft University of Technology, Netherlands

^* Corresponding author: s.farajigargari@uu.nl

Introduction

Coastal dunes act as natural barriers against storm surges, providing essential protection to inland areas. Understanding their formation and evolution is important for developing effective hazard management strategies to protect the mainland. Their morphology is primarily shaped by wind-driven sediment transport, involving a complex two-way interaction between wind flow and the evolving dune surface, which arises from sediment transport. Computational fluid dynamics (CFD) simulations have been widely used to model wind flow over coastal dunes (Gargari et al., 2025), and numerical methods are commonly applied to simulate sediment transport (van Westen et al., 2024). A coupled modeling approach that integrates wind flow and sediment transport is required to better understand dune dynamics.

Objective and Methods

Wind flow and bed level elevations in coastal dunes vary on different scales. This poses challenges when modelling the non-linear feedback relations between varying bed level elevations as a function of varying wind flow and vice versa. Therefore, a numerical investigation of the coupled interactions between wind flow, sediment transport, and morphological change is required. In this study we couple a detailed wind flow (OpenFOAM) model to a sediment transport and morphological change model (AeoLiS). AeoLiS, a numerical package for simulating wind flow and sediment transport, has been successfully applied to model the morphological evolution of coastal dunes over time. However, AeoLiS employs a simplified wind-flow model rather than directly solving the equations governing fluid mechanics, which may reduce accuracy, particularly in cases with complex bed morphology. OpenFOAM, in contrast, provides highly accurate numerical simulations of wind flow by solving the three-dimensional Navier–Stokes equations. However, it does not include a robust sediment transport solver. To address these limitations, this study presents a coupled OpenFOAM–AeoLiS framework that combines the high-fidelity wind-flow simulation capabilities of OpenFOAM with the sediment transport and morphological evolution modeling of AeoLiS. Figure 1 shows the flowchart of the model.

Results

The developed OpenFOAM–AeoLiS model was applied to simulate wind flow and bed morphology changes over time for a pilot case study dune in Egmond aan Zee (Schwarz et al., 2021, Schwarz et al., 2020). Figure 2 shows the dune profile along with the wall shear stress (τ/ρ) distribution computed over the dune. In the presentation, dune profile erosion and sedimentation resulting from the imposed shear stress will be presented.  Future work will focus on validating the coupled model against field measurements to evaluate its predictive performance in real-world applications.

Fig. 1. Flowchart of coupled AeoLiS–OpenFOAM model. Fig. 2. Left: Computed wall shear stress (τ/ρ [m²/s²]) over the dune. Right: Egmond dune profile.

References

Gargari, Saeb Faraji, Derek Karssenberg, and Gerben Ruessink. "The influence of foredune geometry on wind flow quantified from computational fluid dynamics simulations." Aeolian Research 74 (2025): 101001. https://doi.org/10.1016/j.aeolia.2025.101001.

Schwarz, C., C. Van Starrenburg, J. Donker, and G. Ruessink. "Measured data for wind and sand transport across a vegetated foredune slope". Zenodo. 2020. https://zenodo.org/records/4270358.

Schwarz, C., C. Van Starrenburg, J. Donker, and G. Ruessink. "Wind and sand transport across a vegetated foredune slope." Journal of Geophysical Research: Earth Surface 126, no. 1 (2021): e2020JF005732.  https://doi.org/10.1029/2020JF005732.

van Westen, Bart, Sierd de Vries, Nicholas Cohn, Christa van IJzendoorn, Glenn Strypsteen, and Caroline Hallin. "AeoLiS: Numerical modelling of coastal dunes and aeolian landform development for real-world applications." Environmental Modelling & Software 179 (2024): 106093. https://doi.org/10.1016/j.envsoft.2024.106093.