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323. There is a strong evidence base which demonstrates that the changes in the wave regime due to the presence of foundation structures, even under a worst case of the largest diameter gravity base structures (Table 7.3), are both relatively small in magnitude (typically <10% of baseline wave heights in close proximity to each wind turbine, reducing with greater distance from each wind turbine) and relatively localised in spatial extent (extending as a shadow zone typically up to several tens of kilometres from the site along the axis of wave approach, but with low magnitudes (only a few %) of change across this wider area). This is confirmed by a review of modelling studies from around 30 wind farms in the UK and European waters (Seagreen 2012), existing guidance documents (ETSU 2000; ETSU 2002; COWRIE 2009), published research (Ohl et al. 2001) and post-installation monitoring (Cefas 2005).


324. This is further supported by previous numerical modelling of changes in the wave regime under return period events of 1 in 0.1 year, 1 in 1 year and 1 in 10 years, associated with the proposed East Anglia ONE project (ABPmer 2012b). This wave modelling incorporated a worst case of 240 gravity base structures with a basal diameter of 50m. The results were:


 Maximum percentage reductions in baseline wave height occur within or along the boundary of the East Anglia ONE site.


  


During 1 in 10 year storm events, the percentage reductions in wave heights may be up to approximately 20% within the East Anglia ONE site.


At a distance of approximately 40km from the East Anglia ONE site, maximum percentage reductions in wave height are typically less than about 2%.


Regardless of return period or direction of the incoming wave conditions, the presence of an array of foundations within the East Anglia ONE site does not cause a measureable change in wave characteristics at the coast.





Due to proximity of the East Anglia ONE site to the ‘non designated sandbanks’ receptor group and also the Galloper Offshore Windfarm site, wave height reductions of up to about 5% were observed under the largest storm events considered at these locations.


325. The worst case included in the previous wave modelling for the proposed East Anglia ONE project considered 240 gravity base structures with a basal diameter of 50m. Given the water depths experienced across the East Anglia THREE site, the likely envelope of wind turbine numbers and foundation sizes is presented in Table 7.28.


Preliminary Environmental Information May 2014


East Anglia THREE Offshore Windfarm Chapter 7 Marine Geology, Oceanography and Physical Processes Page 64


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