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Table 3. Physical Processes Assessment Methods for East Anglia THREE and FOUR Phase


Potential Impact


Construction and Decommissioning


Changes in suspended sediment concentrations as a result of GBS sea bed preparation activities and drilling for jacket installation.


WCS Details


GBS: 1 foundation installed/day (tbc).


Dredging of surface sediment (to be characterised by grab samples) and disposal by barge (surface release) in close proximity to each foundation.


Jacket: 1 jacket installed/48hrs (tbc). Drill release of sub- surface sediments (to be characterised by boreholes) per jacket. 100% disaggregation into component particle sizes assumed (not considering cohesion and clastic properties).


Proposed Assessment Method Expert-based assessment.


This qualitative assessment will draw from the results of previous Zonal Cumulative Impact Assessment (in the ZEA) and detailed modelling previously undertaken for the East Anglia ONE project (in its ES) and be informed by relevant project-specific survey data from the East Anglia THREE and East Anglia FOUR projects.


Justification


Modelling for East Anglia ONE shows no significant effect from construction or decommissioning activities for that project. Physical conditions and WCS details are similar between East Anglia ONE and both East Anglia THREE and East Anglia FOUR.


Tidal ellipses across the zone show no significant potential for interaction, even within several consecutive tidal cycles, between East Anglia THREE or East Anglia FOUR and sensitive seabed and shoreline receptors.


Sediment characteristics indicate only a very small proportion of fine sediment content and therefore sediment plumes are expected to be limited and sediment will fall to the seabed in relatively close proximity to its point of release into the water column.


Consultation with regulators (Cefas and Natural England) on 10th September 2013 has identified no significant concerns from these construction/decommissioning activities for East Anglia THREE and East Anglia FOUR in relation to potential effects on fisheries or benthic ecology.


Phys_Proc_background Sept 2013


East Anglia THREE & East Anglia FOUR Page 15


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