169. Closer to shore, along the offshore cable corridor, water depths reduce and wave effects become more important in governing sediment transport. At shallow water locations off the East Anglian coast, waves are a combination of short period wind- generated waves, which generally reveal a predominant wave direction from the east, and longer-period swell waves. Both wave types can be influential in mobilising sediment. Along the East Anglian shore itself the wave energy varies significantly and in places is heavily influenced by the sheltering effect of nearshore sandbanks.
7.5.6.1 Climate Change 170. Climate projections indicate that wave heights in the southern North Sea will increase by up to 0.05m by 2100.
7.5.7 Sediment Regime
7.5.7.1 Surface Sediments 171. The sea bed across the East Anglia THREE site is characterised predominantly by sand, with some muddy sand. This is supported by the types of bedforms (sand waves, megaripples, sand ridges) that are present. The areas of muddy sand are in deeper areas and correlate with locations where the surficial sediments are a thin veneer and the underlying muddy Brown Bank Formation is close to sea bed. At these locations bedforms are absent.
172. The median sediment grain size (d50) of a series of grab samples ranges from 0.21 to 0.36mm (medium sand) with a single sample containing a d50 of 0.07mm (very fine sand).
173. The sea bed across the offshore cable corridor is predominantly sand. The median sediment grain size (d50) of a series of grab samples mostly ranges from 0.23 to 0.50mm (medium sand) with a small number of samples with a d50 in the coarse sand or very fine sand classes.
7.5.7.2 Bedload Transport Pathways 174. Sediment transport pathways across the East Anglia Zone have been extensively investigated in previous studies (e.g. HR Wallingford et al. 2002) and through analysis of the orientation of bedforms.
175. Within the East Anglia THREE site, the steeper slopes of the sand waves face to the north or northeast indicating a migration direction, and hence sediment transport, to the north or northeast.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm Chapter 7 Marine Geology, Oceanography and Physical Processes Page 36
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