Abstract
Offshore wind farms (OWF), containing blades, turbines and their bases can interact with the atmosphere or with the surrounding water to form visually-observable features. In the atmosphere, clouds and fog may be formed or dispersed by the movement of spinning turbine blades. For the sea surface, decreases in surface roughness downwind of wind farms have been measured under certain conditions. This is due to a reduction in wind speeds in the lee of the farm. Also visible at the surface, elongated, optically-distinct plumes of turbid water have been observed close to monopiles and for some distance down-current of a wind farm. Turbid wakes can be seen at sea level, from aircraft, and from space and are most frequently observed around wind farms along the east coast of England. The increasing availability of high quality satellite images since 2013 has raised awareness of wind farm / environment interactions. Several scientific papers have been produced in recent years describing the interactions of monopiles with moving water, using numerical modelling and scaled-down flume tank experiments.
Understanding the nature of the monopile wakes, and whether they pose any disturbance to the marine environment, would help the OWF sector better gauge the necessity of monitoring activities. The formation and consequences of turbid wake formation is the subject of the investigations in this report. A combination of satellite remote sensing and fieldwork on the Thanet OWF were used to investigate the causes of turbid wakes. The concentration of suspended particulate matter (SPM) is the main control on water transparency in the southern North Sea, and it was hypothesised that changes in water colour due to monopile-current interactions would result in a higher concentration of sediments in the surface layer.