On the attraction of marine dunes to OWF fixed foundations

Marine dunes, also known as sand waves, are found worldwide, particularly in shallow shelf seas where marine renewable energy projects are often located. Due to their size and mobility, it is crucial for such projects to simulate dune migration and understand interactions with wind turbine foundations. This study builds upon a validated large-scale openTELEMAC model of the Dunkirk coastal area, which combines 3D hydrodynamics with a depth-averaged sediment transport approach. To evaluate the influence of wind turbine fixed foundations on dune migration, we conducted two-year numerical experiments under two contrasting scenarios: with and without foundations, thereby enabling a direct comparison with the natural baseline. The results indicate that the monopiles act as morphodynamic magnets, altering dune propagation with changes of up to a factor of 4 in their lee. We call the underlying mechanism the ‘wake effect’, where reduced flow velocity and sediment transport down-current of the monopile lead to increased migration rates when dunes approach the foundation and decreased (or reversed) rates when moving away. The results also highlight the cumulative effect of monopiles on sediment transport in a scenario with 46 wind turbines, emphasising the need for careful turbine placement to mitigate impacts on the dune field.