Table 7.3 Worst Case Assumptions for Foundation Footprint Foundation Type


Water Depth (m)


Gravity base structure <35


Jacket* (dimensions are distances between leg centres based on a square footprint)


Suction caisson Monopile


35 – 45 45 – 55 <35


35 – 45 45 – 55 Up to 50 <35


35 – 45 30.


50 (basal diameter) 55 (basal diameter) 60 (basal diameter) 35x35


37.5x37.5 40x40


30 (diameter) 7.5 (diameter) 12 (diameter)


Foundation Dimensions (m)


Foundation Footprint (m2)


1,963 2,375 2,827 1,225 1,406 1,600 706 44


113 * Jackets would have 3 or 4 legs and be founded on either pin piles or suction buckets.


In respect of sediment disturbance effects, these can be considered separately for the construction phase, the operation phase and the decommissioning phase.


31. During the construction phase, it is probable that there would be a need for some sea bed preparation associated with all foundation types. This has potential to disturb sediments at or near the surface of the sea bed (down to relatively shallow depths below the sea bed), hereafter called near-surface sediments.


32.


The greatest quantities of near-surface sediment disturbance due to sea bed preparation activities during construction would be associated with conical gravity base structures. Conservative average dredging volumes associated with conical gravity base structures of the maximum diameter for both the 7MW and 12MW wind turbines are provided in Table 7.4. To ensure a conservative approach to the assessment of effects, it has been assumed that these values apply everywhere across the East Anglia THREE site, but in reality the foundation diameters would vary according to water depth.


Preliminary Environmental Information May 2014


East Anglia THREE Offshore Windfarm Chapter 7 Marine Geology, Oceanography and Physical Processes Page 8


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