Numerical modelling of airflow and sediment transport patterns over Aeolian coastal sand dunes: Effects of dune slope and wind direction

This study explores the influence of incident wind angles and dune slope on near-bed wind flow and sediment transport patterns over dunes, using a three-dimensional Computational Fluid Dynamics model in OpenFOAM. The Bagnold sediment transport formula, adjusted for slope effects, alongside the Exner equation, is employed to simulate sediment transport and morphological changes. The Full-scale dune profile modelling, representative of the Hondsbossche Dunes in the Netherlands, uncovers three distinct flow regimes, showing the significant dependence of sediment transport on both wind direction and slope inclination. The study highlights that sedimentation accumulation around the toe of an unvegetated dune is most substantial for a slope inclination of 20° and wind flowing normal towards the dune. While more oblique winds, typical for the Netherlands, result in decreased and less slope-dependent sediment deposition at the dune toe. The findings indicate that in the absence of vegetation, the dune slope is vulnerable to considerable erosion under a variety of wind conditions. Incorporating vegetation into the model significantly reduces erosion on the slope, resulting in most of the sediment being deposited at the dune toe and only a minor amount just beyond the crest. This finding is consistent with the sedimentation patterns at the Hondsbossche Dunes, revealing the vital role of vegetation in dune stability. Notably, on steeper slopes, exceeding an inclination of approximately 50°, vegetation does not markedly alter sedimentation at the dune toe compared to the dunes without vegetation.