Scour variability across offshore wind farms (OWFs): Understanding site-specific scour drivers as a step towards assessing potential impacts on the marine environment

Abstract. The development of offshore wind farms (OWFs) is critical to meeting renewable energy targets, but predicting scour around offshore wind energy structures (OWES) and the associated potential impacts on marine ecosystems remains a challenge. Using high-resolution bathymetry data, this study analyses field-measured scour depths at 460 monopiles at nine British OWFs. The analysis reveals a large spatial variability of relative scour depths (𝑆/𝐷) between OWF sites, but also within individual wind farms. Principal component analysis (PCA) is used to identify significant drivers of this variability. When the entire data set is considered, results indicate that median grain size (𝐷₅₀), relative water depths (ℎ/𝐷), and the significant wave height (𝐻_𝑠,99) are the most important influencing factors for the variability of scour depths. Other parameters investigated, such as Froude number (𝐹𝑟), pile Reynolds number (𝑅𝑒), flow intensity (𝑈_𝑐,99/𝑈_𝑐𝑟), and current velocity (𝑈_𝑐,99), were found to have a less clear influence. Further sediment-specific analysis shows that relative water depth (ℎ/𝐷) is a particularly relevant driver of scour at sites with fine (63 to 200 𝜇𝑚) and medium sands (200 to 630 𝜇𝑚), with larger scour depths occurring in shallower water depths. Findings from this study provide new insights into scour behavior across a range of spatial and environmental scales and lay a foundation for the transferability of scour prediction frameworks to new OWF sites. In the future, findings and datasets from this study are suggested to be used to estimate scour-induced sediment transport and thereby to provide a step towards the assessment of potential impacts of OWF expansion scenarios in the marine environment. By addressing the broader implications for regional sediment dynamics, this research contributes to the sustainable development of offshore wind energy.