Scour Estimation at Offshore Wind Farms: Notes from Europe and Implications for the Eastern United States

Recently, the planning for offshore wind farms (OWFs) has begun in earnest along the United States Atlantic outer continental shelf (OCS). However, the vast majority of all OWFs constructed to date are located along coastal Europe. These OWFs employ fixed-foundation turbine structures, consisting of monopile or jacket foundations supporting the turbine itself. Just as bridges contend with foundation scour where the structure meets the riverbed, so too must fixed-foundation turbine structures contend with scour at the seabed. These scour patterns are complex and carry both local and farther-field impacts. The empirical techniques that have been utilized over the past decade to quantify foundation scour at turbine foundations are tailored for the shallow, high-velocity environments typical of the European coastline. Many of the OWFs installed in this region are situated in shallow waters less than 20 meters deep, where seafloor sediment dynamics are driven by both currents and waves. Scour estimation for these structures relies on the magnitude of the Keulegan-Carpenter number to characterize the erosive impacts of lee-wake vortices caused by waves in addition to the horseshoe vortices caused by currents. Along the US Atlantic OCS, waters tend to be deeper and currents calmer than at coastal European sites, reducing the effect of wave energy on the seafloor sediment transport regime. In this presentation, we review the analytical methods used to estimate local scour for foundation structures at OWFs in Europe. Then, we present an approach to estimate local scour tailored to Atlantic OCS using long-term time series of hydrodynamic and wave datasets.