Plate 7.2.1. Grab sample at AWAC deployment location within the proposed East Anglia THREE site 83.


Fugro EMU (2013a) collected multibeam backscatter data and side scan sonar images across the East Anglia THREE site, and combined this with the zone-wide particle size data to interpret sea bed sediment distribution. The sea bed is homogeneous and is characterised by mainly sand with some muddy sand. This is supported by the types of bedforms (sand waves, megaripples, sand ridges) that are present across the East Anglia THREE site. The areas of muddy sand are in deeper areas and correlate with locations where the surface sediments are a thin veneer and the underlying muddy Brown Bank Formation is close to sea bed. At these locations bedforms are absent.


84. As part of the zone-wide survey, a total of 47 samples were also collected within the offshore cable corridor. The median particle size (d50) and percentages of mud, sand and gravel are available from these datasets. A follow-up benthic survey within the offshore cable corridor was also undertaken in April and May 2013, from which a further 39 sea bed sediment samples were collected (Fugro EMU 2013c). Detailed particle size analysis is also available for these further 39 samples.


85.


The 47 samples collected during the zone-wide survey show that the predominant sea bed sediment along the cable route is sand (Table 7.2.5). The proportion of sand ranges from 57% to 99%, with the majority of samples (43 no.) containing greater than 83% sand. The gravel content varies from zero to 14% in 43 samples, with the other four containing between 18% and 41% of gravel. All samples contain less than 5% mud with the majority (44 no.) containing less than 3%. The d50 along the offshore cable corridor ranges from 0.30mm to 0.50mm (medium sand) with a single sample with a d50 of 0.77m (coarse sand) (Table 7.2.5).


Preliminary Environmental Information May 2014


East Anglia THREE Offshore Windfarm


Appendix 7.2 Page 24


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