Impact
Impact 2: Smothering due to increased suspended sediment
Key design parameters forming the worst case scenario
As per details in construction impact 2 (above) for increased suspended sediment concentration and sediment deposition (although predicted to be much less in reality – see comment under rationale).
Rationale
Any impacts produced during decommissioning would be less than those described during the construction phase (Construction impact 1) due to absence of sea bed preparation, which is the main source of increased suspended sediment concentration during the construction phase.
Impact 3: Re-mobilisation of contaminated sediments
Impact 4: Underwater noise and vibration
As per details in construction impact 3 (above) for re-mobilisation of contaminated sediments (although predicted to be much less in reality.
Noise created by the removal of foundations using cutting machinery See text in the row above
The removal of monopiles or piles for jacket foundations to 1- 2m below sea bed level is likely to involve the use of cutting machinery. This is would create underwater noise and vibration which is likely to be substantially less than that created during the installation of monopiles
Impact 5: Loss of habitats and species colonising hard structures
As per details in operation impact 5 above. It is assumed that all colonised hard substrate would be removed see Chapter 5 Description of the development.
Assumed that all project infrastructure above sea bed level would be removed during decommissioning, resulting in the loss of colonised substrate.
Note: that there would be up to two cables to interconnect the proposed East Anglia THREE and East Anglia ONE projects. The cables would either be two cables, subject to detailed design and future technology developments. Each would be up to 90km in length. The locations where these interconnections join the East Anglia ONE electrical infrastructure would be identified following detailed electrical design and would be dependent upon the location of the East Anglia ONE converter stations. These cables have not been assessed as part of the worst case and once interconnection cable routeing has been determined they will be added into the assessment.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 10 Benthic Ecology Page 16
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