•
Changes to Composition of Demersal Spawning Grounds.
GBS Foundation Preparation and Installation 87. As reported in Chapter 7 Marine Geology, Oceanography and Physical Processes, measurements of suspended particulate matter (SPM) within the proposed East Anglia THREE site as part of the metocean survey showed naturally occurring concentrations of 3 - 13.5mg/l throughout the winter of 2012/13. As expected, suspended sediment concentrations increase considerably closer to the coast, with levels up to 170mg/l recorded in the vicinity of Great Yarmouth (ABPmer 2012).
88.
For the installation of GBS foundations the worst case scenario involves excavation of the sea bed to level an area of sand waves up to 5m in height, with a maximum volume of excavation of 26, 000m3 per foundation.
89. 90.
Impacts of foundation installation on sediment suspension and re deposition are discussed in chapter 7 Marine Geology, Oceanography and physical processes.
Considering the relatively short duration and limited spatial extent of the effect, the magnitude of any impacts is assessed as low.
Drilling Operations 91. During the installation of monopile foundations drilling maybe necessary if ground conditions are found to be unfavourable. The disposal of drill cuttings would result in increased SSCs where operations are being undertaken.
92.
The worst case scenario assumes that a 12m diameter monopile foundation would be drilled from the sea bed surface to a depth of 60m below the sea bed surface, releasing 3,524m3 of sediment into the water column.
93. 94.
Impacts of the disposal of drill arisings are discussed in Chapter 7 Marine Geology, Oceanography and Physical Processes.
Considering the relatively short duration and restricted spatial extent of the effect, the magnitude of any impacts is assessed as low.
Inter-Array and Export Cable Installation 95.
Inter-array cable installation, has the potential to disturb sediments from the sea bed to shallow depths of up to 5m. The magnitude of effect that could be caused is assessed in Chapter 7 Marine Geology, Oceanography and Physical Processes. The magnitude would be considerably lower than that created by the installation of foundations as the overall sediment release volumes would be lower and confined to near the sea bed (rather than higher in the water column) along the alignment of the
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 11 Fish and Shellfish Page 48
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