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north-northeast in the south of the Zone. A general north-south reduction in maximum observed wave heights occurs across the Zone. On the northern boundary, a 1 in 50 year return period event has a significant wave height in excess of 8m whereas on the southern boundary a corresponding event has a significant wave height below 6.5m.


11. Across the majority of the Zone, water depths are likely to be sufficient to limit the effect of wave action on seabed sediments, apart from during exceptionally stormy seas or over shallower areas.


12.


Closer to shore, however, water depths reduce and wave effects become more important. At shallow water locations off the East Anglian coast, waves are dominated by short period wind-waves and generally reveal a predominant wave direction from the east. Along the shore itself the wave energy varies significantly and in places is heavily influenced by the sheltering effect of nearshore banks.


13. 5. 14.


Climate projections indicate that wave heights in the southern North Sea will only increase by between 0 and 0.05m by 2100.


Sediment regime


The geology within the Zone generally consists of geologically recent superficial sand deposits overlying a series of Quaternary sands and clays. The depth of surficial sediment across the Zone varies from <1m across most of the site to greater than 20m in the sandwave fields and on the sandbanks, especially to the north of the Zone.


15.


The grab samples collected across the Zone correspond well with existing BGS seabed sediment data and reveal that across 90% of the Zone the Holocene sediments consist of either sand, slightly gravelly sand or gravelly sand. Remaining areas are primarily characterised by sandy gravel, although there are localised pockets of muddy sand and (slightly) gravelly muddy sand present. However, over 85% of the grabs contained less than 5% mud-sized material. The median grain size from over 75% of the samples was within the medium sand range (250 – 500 microns). Between 80-100% of the gravel sized fraction comprises biogenic material (e.g. shells and shell fragments). Some boulders are scattered across the seabed within the Zone.


Phys_Proc_background Sept 2013


East Anglia THREE & East Anglia FOUR Page 29


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