East Anglia THREE project and therefore there is potential for cumulative impacts to arise during the construction and decommissioning stages. Given the phased construction of offshore cable installation (including landfall works) for each of these projects, it is unlikely that there would be overlap in export cable installation between the proposed East Anglia THREE and East Anglia ONE projects however, the possibility of overlap between the installation of the East Anglia THREE and East Anglia FOUR offshore export cables exists. Given the significance of impact assessed in construction impacts 5 and 6 (sections 7.6.1.5 and 7.6.1.6) it is not considered that cumulative impact of two projects constructing in this area at the same time would be greater than negligible.
408. In order to assess the potential for effects arising cumulatively between the installation of the offshore export cable for the proposed East Anglia THREE project and marine aggregate dredging activities in adjacent areas of sea bed, reference has been made to the EIA for the proposed East Anglia ONE project. This EIA was supported by numerical modelling, using Delft3D plume modelling software, of the potential for interactions of sediment plumes arising from offshore cable installation with those arising from marine aggregate dredging sites (and indeed other sea bed activities) located within one spring tidal excursion distance from the East Anglia ONE offshore cable corridor. The modelling showed that some interaction could potentially occur between dredging plumes and plumes from cable installation and that the spatial extent of the combined plume is slightly greater than for the plumes originating from the offshore export cable installation only. Whilst maximum plume concentrations would be no greater under the cumulative scenario, a larger geographical area might experience increases in suspended sediment concentrations of more than 40mg/l than for the offshore export cable installation only scenario. Following cessation of cable burial and aggregate dredging activities, a few hundred metres away from the immediate release locations maximum theoretical bed level changes of up to 2mm were observed, with maximum levels of around 0.8mm at greater distances.
409. Given that the landfall and inshore sections of the East Anglia THREE offshore cable corridor are exactly coincident with those assessed for the East Anglia ONE offshore cable corridor, and elsewhere to the western edge of the East Anglia Zone the East Anglia THREE offshore cable corridor encompasses that for East Anglia ONE, it is also considered the potential cumulative impacts between offshore cable installation and nearby marine aggregate dredging activities would be negligible.
410. The cumulative impact assessment findings presented above are consistent with the findings of the earlier ZEA in relation to marine geology, oceanography and physical
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm Chapter 7 Marine Geology, Oceanography and Physical Processes Page 79
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