Quantification of turbid wakes in offshore wind farms using satellite remote sensing
Enora Maëlanne Lecordier, Pierre Gernez, Krysia Mazik, Katharine York, Rodney Forster
Abstract
The offshore wind (OSW) industry is expanding globally, particularly in areas of shallow water such as the North Sea. The environmental impacts of large-scale offshore development are not yet well understood. Satellite remote sensing has shown an increase in suspended particulate matter (SPM) concentration in the wake of wind turbines' foundations due to turbulence in the current flow when encountering the structures. High-resolution Sentinel-2 and Landsat-8/9 satellite observations were used to quantify sediment concentration in the wakes at a range of sites across the southern North Sea. The sites studied had different water depths as well as different types of foundations, and different hydrodynamic conditions, allowing a variety of forcing factors to be related to observed sediment wake intensity. A Random Forest model was built to predict the increase in the amount of suspended sediment observed in wakes downstream of a foundation. Foundation types of large diameter such as gravity-based and monopile produced more intense wakes than jacket foundations. Also, sediment wake intensity followed a seasonal pattern, where the highest SPM concentration was observed during spring. The main factors driving sediment wake intensity are the synergy of wind and hydrodynamic forces alongside the concentration of suspended sediment already present in the area. When turbid wakes are present, increased surface sediment concentration inside and downstream of OSW farms is likely to reduce underwater light availability. This study showed that sediment concentration within turbid wakes can be quantified and predicted by employing the knowledge of the structure's construction type and environmental conditions.