Assessing the impacts of offshore wind turbines on suspended sediments concentration in northern China coastal waters on the basis of Sentinel-1/2

The disturbance by offshore wind turbines on water, brings strong vertical mixing of substances in the water, which not only impacts the aquatic ecosystem but also threatens the stability of pile foundations for offshore wind turbines. The suspended sediment concentration (SSC) serves as a reliable index for monitoring the effects of wind turbines on water mass. This study utilizes Sentinel-1 SAR satellite images to identify offshore wind turbines and to monitor the evolution of wind farms in northern China coastal waters, while Sentinel-2 optical satellite is used to monitor the Scaled Index of Suspended Sediments Wake (SI-SSW) caused by wind turbines. The results derived from Sentinel-1 images show that the total area of offshore wind farms increased to about 6300 km² by 15 times over the past decade, with an increase in the total number of offshore wind turbines from 322 in 2016 to 3840 in 2024 and an expansion in distribution towards deep sea. The results from Sentinel-2 optical imagery show that the affected area by one single wind turbine indicated by the SSC and the SI-SSW ranged from 0.3 km² to 1.5 km², which means about 5800 km² of water was affected by wind farms in the northern China coastal waters. The SSC, due to resuspension, could be elevated by more than 20% in the wind turbine wakes. In this work, the effects of tidal patterns, water depth, and the volume of the turbine's foundation on the wakes are also explored. The proposed methods and the findings would provide supports on assessing the impacts of offshore wind farms and the related decision-making.