2013, HR Wallingford, Greater Gabbard Offshore Wind Farm Limited, Post-Installation Scour Assessment

Description

SSE Offshore Wind Generation requested HR Wallingford to perform a scour review based on the 2013 inter-array cable survey data at the Greater Gabbard Offshore Wind Farm (OWF). The survey data was assessed at every turbine location to provide descriptive scour parameters and to provide a baseline description for future asset management.
The Greater Gabbard offshore wind farm site is located about 23 km (14 miles) off the Suffolk coast and comprises 140 turbines near the Inner Gabbard and Galloper sandbanks, making it currently one of the largest offshore wind farms (OWF) in the world. As part of the existing licence agreement with the Marine Management Organisation, SSE is required to perform yearly (for up to three years) high-resolution swath-bathymetry surveys of the OWF cable route in order to assess the extent of any changes in morphology relative to the pre-construction baseline survey.
HR Wallingford has previously investigated whether apparent magnitude of seabed movements observed in the 2013 survey data had a physical basis or were attributable to inaccuracies and errors in surveying and/or GPS positioning. The results of this study demonstrated that the 2013 survey data was subject to a total vertical uncertainty of ±0.35 m. The total vertical uncertainty (TVU) is defined by the International Hydrographic Organisation (2008) as that component of the total propagated uncertainty (TPU) in the vertical dimension, where TPU is the result of uncertainty propagation, when all contributing measurement uncertainties, both random and systematic, have been included in the propagation. The report presented analysis of bed level movements across the wind farm array cable routes. The current report evaluates the foundation scour development using the same data.