Scour variability across offshore wind farms (OWFs): identifying 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 (OWESs) 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 in relative scour depth (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 dataset is considered, results indicate that the relative water depth (h/D), the relative median grain size (d50/D), the Keulegan–Carpenter number (KC99), and the sediment mobility parameter MOB (θ99/θcr) are the most important influencing factors for the variability in relative scour depth. Other parameters investigated, such as pile Reynolds number (Re99), flow intensity (U/Ucr)99, and Froude number (Fr99), 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 ≤ d50 < 200 µm) and medium sands (200 ≤ d50 < 630 µm), with larger relative scour depth occurring at shallower relative water depths. Findings from this study provide new insights into scour behaviour 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.