Influence of Offshore Wind Farm Monopiles on Multi-Scale Hydrodynamics and Sediment Transport in a Wave-Current Environment

The rapid expansion of offshore wind energy infrastructure represents a major anthropogenic modification of coastal and marginal seas, yet the physical interactions between monopile foundations, hydrodynamics, and sediment transport remain insufficiently quantified. This study investigates the impact of monopile foundations at the Meerwind offshore wind farm (German Bight, North Sea) on local and regional coastal dynamics. Using a high-resolution coupled wave-current-sediment transport model, we analyze hydrodynamic and sediment processes with mesh refinement of ~2 m near the structures to capture turbulent wake effects.

Our results demonstrate that monopile arrays act as significant sinks for wave energy: monthly mean significant wave heights (Hs) and mid-depth velocities decrease by ~5%, while turbulent kinetic energy increases by up to 70% near the foundations. Dominant westerly wind-driven waves modulate tidal asymmetry on the leeward (eastern) side of the piles, generating asymmetric turbulent wakes and altering bottom shear stress patterns.

Reduced wave-induced bottom stress enhances localized sediment deposition, increasing surface suspended sediment concentration (SSC) while reducing near-bottom loads. On a regional scale, wave attenuation leads to a ~1% decrease in depth-averaged SSC over a 20 km east of the piles. In consequence, the presence of the wind farm reduces the net inflowing sediment flux by ~25% within a 5 km radius during March 2020, linked to a ~2 cm attenuation of Hs.

These findings highlight how large-scale offshore energy infrastructure can reorganize sediment budgets and coastal morphodynamics under changing human activities, providing critical insights for the sustainable management of multi-use ocean spaces. Further work, including additional wind farms and extended simulation periods, is planned to substantiate these initial findings and better quantify cumulative impacts, particularly in light of ongoing erosion challenges in the Wadden Sea under sea-level rise.