Sandwaves and megaripples at Race Bank (UK) Offshore Wind Farm

Larsen, S. and Roulund, A. and Brooks, A. and Chaffey, A. (2016) Sandwaves and megaripples at Race Bank (UK) Offshore Wind Farm. In: ICSE 2016 (8th International Conference on Scour and Erosion), 12-15 September 2016, Oxford, UK.

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Abstract

The Race Bank Offshore Windfarm is part of the UK Round 2 extension. The windfarm comprises 91 6.3 MW turbines and two substations with total installed power of 573 MW. Construction work is scheduled for 2016/17. The windfarm is located in UK waters in the southern part of the North Sea about 30 km north of the Norfolk coastline and 30 km east of Lincolnshire. The Race Bank site has a diverse morphology located on large sandbanks with mobile sandwaves and megaripples and intersected by deeper featureless swales where clay soil formations are found close to or at the sea floor. The morphological complexity of the site was recognised early in the project development and numerous bathymetric surveys have been undertaken to help quantify sandwave migration rates and expected seabed variability. Morphological seabed assessments have been conducted by ABPmer throughout the project development. In the detailed design phase the ABPmer assessments have been combined with in-house DONG Energy analysis to provide design seabed levels and anticipated ranges of natural seabed changes within the lifetime of the windfarm. The paper presents an overall morphological characterisation of the windfarm site and provides examples of the very diverse seabed morphology encountered. When quantified, the morphological diversity can be absorbed in the monopile foundation design and cable installation contractors can select appropriate installation tools. The paper thus comes with a recommendation to ensure that bathymetric surveys in morphological active sites are carried out early and repeatedly during the project development stages.

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