The impact of offshore wind farms on the marine environment goes far beyond their own location.
Offshore wind turbines extract energy from the wind and thus influence the wind speed at the sea surface. This has implications for the mixing of the water as well as its current speed. These are well-known effects that are traced back to the wind turbines. However, the piles of the wind turbines also influence the marine environment far beyond their own location, as Hereon researchers have now shown with regional ocean models.
The piles therefore pose a great resistance to the ocean current and thus disrupt the natural flow of the water. As a result, they cause turbulence that changes the mixing of the water, meaning the distribution of temperature and salts between the surface and bottom layers. This can in turn affect the distribution of nutrients between the water layers and thus primary production. Another effect of the turbulence is a reduced current speed downstream, that is, in the direction of the tidal current, which is decisive for sediment transport. At ten per cent, the changes caused this way are still in the same range as annual fluctuations that occur naturally in ocean dynamics.
“We see that the impacts of local turbulence effects extend far beyond the boundaries of the wind farms. Now we need to find out how these effects interact with the impacts of wind decrease and what consequences this entails for the ecosystem,” says Nils Christiansen, lead author of the study and scientist at the Institute of Coastal Systems – Analysis and Modeling. (Source: Hereon News)
Read the complete Hereon News:
==> Larger than expected
Christiansen, N., Carpenter, J.R., Daewel, U., Suzuki, N., & Schrum, C. (2023): The large-scale impact of anthropogenic mixing by offshore wind turbine foundations in the shallow North Sea. Front. Mar. Sci., 10:1178330, doi:10.3389/fmars.2023.1178330
Abstract:
Structure drag from offshore wind turbines and its physical impacts on the marine environment of the German Bight are investigated in this study. The flow past vertical cylinders, such as wind turbine foundations, and associated turbulent mixing has long been studied, but questions remain about anticipated regional implications of offshore wind infrastructure on physical and biogeochemical conditions. Here, we present two existing modeling approaches for simulating wind turbine foundation effects in regional ocean models and discuss the problematic use of very high resolution in hydrostatic modeling. By implementing a low-resolution structure drag parameterization in an unstructured-grid model, we demonstrate the impacts of monopile drag on hydrodynamic conditions, validated against recent in-situ measurements. Although the anthropogenic mixing is confined at wind farm sites, our simulations show that structure-induced mixing affects much larger, regional scales. The additional turbulence production emerges as the driving mechanism behind the monopile impacts, leading to changes in both the current velocities and stratification, with magnitudes of about 10%, similar in magnitude to regional annual and interannual variabilities. This study provides new insights into the hydrodynamic impact of offshore wind farms at their current development levels and emphasizes the need for further research in view of potential restructuring of the future coastal environment.