needed in the London Clay in the nearshore zone (See Chapter 7 Marine Geology, Oceanography and Physical Processes Impact 7.6.1.8). However, these effects would be highly localised and temporary in duration. The trenching into London Clay would likely result in clumps of material to be displaced and back-filled, rather than the material breaking down into its constituent silt and clay particles. It is therefore unlikely that significant changes in suspended sediment concentration would occur during these works. The back-filling of the trench would result in no noticeable change in coastal morphology after completion of the offshore cable installation at the landfall location and therefore the magnitude of the impact would be low.
202. The impact of increased suspended sediment and smothering would only be observed in the lower shore environment. The lower shore is described as ‘littoral coarse sediment’ (A2.1) using the EUNIS codes and
LS.LCS.Sh.Bar.Sh (Barren littoral shingle) using the MNCR scheme. This habitat is very common along North Sea coastlines and due to the barren nature the ecology which exists, this biotope is not considered sensitive to increased suspended sediment or smothering. Furthermore, it is considered likely that the environment at the landfall location would regularly receive greatly increased levels of suspended sediment and smothering through natural events including storms and so the existing environment would be well adapted to such events.
203. The sensitivity of the receptors to the impact of increased suspended sediment and smothering to species and habitats present at the landfall would be negligible. With the negligible sensitivity and low magnitude of effect the impact is considered to be of negligible significance at the landfall.
10.6.1.2.3 Receptors Across Both Offshore Cable Corridor and the East Anglia THREE site 204. S. spinulosa thrives in conditions of elevated turbidity, which it uses to build the tubes within which it lives. Reefs are tolerant of short-term smothering but in the long-term sediment deposition may result in reduced growth and impaired feeding ability (OSPAR 2010). However, a study carried out by Last et al. (2011) found that S. spinulosa reef is tolerant of burial for up to 32 days and continues to build tubes while buried. Further evidence compiled by Marine Aggregate Levy Sustainability Fund (MALSF) found that there were no adverse effect due to increased suspended sediment to S. spinulosa reefs found within close proximity to active aggregate dredging sites (Pearce et al. 2011b).
205. These results indicate that increased suspended sediment and smothering would not have a detrimental impact on S. spinulosa reef and as a result a low magnitude of sensitivity is assigned. With the embedded mitigation designed to avoid interaction
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 1 Introduction Page 68
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