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262. These effects on sea bed level are considered highly unlikely to have the potential to impact directly upon the identified receptor groups for marine geology, oceanography and physical processes. This is because the magnitude of effects is lower than those associated with foundation installation and there is a large separation distance (well beyond one tidal ellipse) which does not support the existence of a pathway between the source and receptor.


263. The overall impact of inter-array cable installation activities under a worst case scenario on bed level changes for identified morphological receptor groups is regarded as no impact.


264. In many parts of the East Anglia THREE site there would not be the need for release of such volumes of sediment as considered under this worst case scenario and optimisation of inter-array alignment, depth and installation methods during detailed design would ensure that impacts are minimised.


265. The effects on sea bed level also have the potential to impact upon other receptors and therefore the assessment of impact significance is addressed within relevant chapters of the PEIR, taking into consideration the tidal ellipses presented in Figure 7.4, which represent the potential pathways between the source and receptor.


7.6.1.5 Impact 5: Changes in suspended sediment concentrations during offshore HVDC export cable installation


266. The detail of the offshore export cabling is dependent upon the final project design, but present estimates are that the maximum total length of each export cable could be up to 155km in length with up to four cables being installed providing a total maximum length of 620km of export cable. The worst case cable laying technique is considered to be jetting. The offshore cable corridor is fully coincident with that of the proposed East Anglia FOUR project and the furthest inshore section and landfall is coincident with that previously assessed for the proposed East Anglia ONE project.


267. The installation of the offshore cabling has the potential to disturb the sea bed down to a sediment thickness of up to 5m, either directly through the installation method chosen, or through sea bed levelling of any large sand waves that may be present along the offshore cable corridor prior to cable installation. The release of sediment from both of these construction phase activities, with the release points being along the offshore cable corridor, has been considered here.


268. The assessment of changes in suspended sediment concentrations during offshore cable installation has been considered separately from those for the inter-array


Preliminary Environmental Information May 2014


East Anglia THREE Offshore Windfarm Chapter 7 Marine Geology, Oceanography and Physical Processes Page 53


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