Table 10.2.Worst Case Assumptions Impact Construction
Impact 1: Temporary physical disturbance
The maximum area of disturbance during construction would be approximately 34.86km2 across the East Anglia THREE site and offshore cable corridor based on the following:
1. Sea bed disturbance for 60m gravity base foundations and scour protection calculated as 25,500m2 per foundation (see Chapter 7 Marine Geology, Oceanography and physical processes Table 7.4). Therefore for 106 foundations (see Rationale column) the maximum area of disturbance would be 2.68km2.
2. Sea bed disturbance for up to two meteorological masts and scour protection each 2,830m2 totalling a 0.01km2 area.
3. Jack up barge sea bed footprint for 180 foundations (based on a jack up barge footprint of 1,200m2and three movements per foundation) the maximum disturbance would be 0.65km2
4. Installation of up to 550km inter-array cables and 195km HVAC export cables between collector and converter stations. Therefore the maximum disturbed area (with worst case trench width of 10m and 5m spoil width either side of that) of 14.9km2.
Total maximumfootprint during construction within the East Anglia THREE site would therefore be
18.26.km2 (5.99% of the East Anglia THREE site).
5. Installation of up to 620km of HVDC export cable (with worst case width of 10m wide trench and a 5m spoil width either side of trench) would result in a maximum disturbed area of 12.4km2
Total footprint during construction within the offshore cable corridor would therefore be 12.4km2. (1.48% of the offshore cable corridor)
The overall total footprint of the proposed East Anglia THREE project is 30.66km2 (2.68% of the proposed East Anglia THREE project).
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
The largest wind turbines (12MW) would be installed on 60m diameter gravity base foundations and therefore the worst case would be 100 wind turbine foundations with their associated scour protection (a larger number (172) of the smaller (40m diameter) gravity base foundations and associated scour protection results in a smaller area of disturbance).
If scour protection is applied it is likely to be in the form of rock, concrete mattresses, sand-filled geotextile bags, or similar.
It has been assumed that the worst case for up to five foundations for converter and collector stations, and one accommodation platform would result in a similar amount of sea bed preparation as that for a wind turbine foundation.
Up to two meteorological masts may be installed using gravity base foundations.
Much of this calculated area would be only temporarily disturbed (i.e. anything related to cable installation). It is anticipated that a small proportion of it (the physical footprint of the proposed project) would represent permanent habitat loss. Operation Impact 1 assesses the impact of permanent habitat loss. An overlap would occur where there is a temporary physical disturbance (for example with sea bed preparation) with an area which then suffers permanent habitat loss through infrastructure being placed on that location. By assessing the two impacts (Construction
Chapter 10 Benthic Ecology Page 9
Key design parameters forming the worst case scenario Rationale
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