142. Specific investigations have also been made at the landfall of the offshore cable corridor for East Anglia THREE to characterise the shoreline (ABPmer 2012c) and the changes in sea bed and shoreline over time (ABPmer 2013).
143. To inform the proposed East Anglia THREE project, further metocean, geophysical and grab sample surveys have been undertaken. These surveys are summarised in the earlier Table 7.10.
7.5.2 Bathymetry and Morphology 144. Water depths within the East Anglia THREE site vary from a maximum depth of 49m below LAT across the western part of the project site to a minimum depth of 25m below LAT on the crest of a sand ridge in the centre of the project site (Figure 7.2).
145. The bathymetry is dominated by a series of three north-south oriented sand ridges with widths of 2 to 3km and heights of up to 17m above the surrounding sea bed. Smaller bedforms, including sand waves (greater than 2m high), megaripples (less than 2m high) and sand ribbons, are present throughout the East Anglia THREE site.
146. Asymmetric sand waves occur across approximately 50% of the sea bed of the East Anglia THREE site. Where they are present along the tops of the sand ridges, their crests are oriented predominantly northwest to southeast. In deeper locations, the crests are oriented more west to east. The sand waves have wavelengths of 200 to 300m and heights of 2 to 7m and their flanks are generally covered by megaripples.
147. Megaripples are common throughout the site. They have typical wavelengths of 5 to 20m and heights of 0.3 to 2m, and their crests are oriented west to east.
148. Sand ribbons are occasional bedforms aligned south-southwest to north-northeast. They have widths of 20 to 100m and heights of about 0.5 to 1.5m and may be covered in megaripples or occasional sand waves. Sand ribbons form in areas where tidal currents are strong. They are located across the deeper parts of the East Anglia THREE site where sand is less abundant.
149. Example images from the geophysical survey of the sand ridges, sand waves, megaripples and sand ribbons can be seen in Appendix 7.2 Diagram 7.2.1.
7.5.3 Geology 150. The geology of the East Anglia THREE site comprises three geological formations; in ascending order (older to younger) these are the Pleistocene Yarmouth Roads Formation comprising 0 to 100m thick riverine sands and channel infills, overlain by the 5 to 10m thick mud of the Pleistocene Brown Bank Formation, topped by 0 to 20m of Holocene sand.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm Chapter 7 Marine Geology, Oceanography and Physical Processes Page 33
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