given water depth. In practice, the volumes of sediment released would be lower than the worst case at many wind turbine locations because the detailed design process would optimise the foundation type and installation method to the site conditions.
250. The effects on sea bed level have the potential to impact upon other receptors and therefore the assessment of impact significance is addressed within relevant chapters of the PEIR, taking into consideration the tidal ellipses presented in Figure 7.4, which represent the potential pathways between the source and receptor.
7.6.1.3 Impact 3: Changes in suspended sediment concentrations during inter-array cable installation
251. The detail of the inter-array cabling is dependent upon the final project design, but present estimates are that the total length of inter-array cables for the project may be in the range up to 550km and the worst case cable laying technique is considered to be jetting.
252. The installation of the inter-array cabling has the potential to disturb the sea bed down to a sediment thickness of up to 5m, either directly through the installation method chosen, or through sea bed levelling of any large sand waves that may be present along the route of any inter-array cables prior to cable installation.
253. The types and magnitudes of effects that could be caused have previously been assessed within an industry best practice document on cabling techniques (BERR 2008). This document has been used alongside expert-based judgement and analysis of site conditions to inform the assessments presented below.
7.6.1.3.1 Assessment of effect magnitude and/or impact significance 254. It is anticipated using expert-based assessment that the changes in suspended sediment concentration due to inter-array cable installation would be lower than those arising from the disturbance of sea bed surface and near-bed sediments during foundation installation activities including sea bed preparation.
255. This is because the overall sediment release volumes would be low and confined to near the sea bed (rather than higher in the water column) along the alignment of the inter-array cables, and the rate at which the sediment is released into the water column from the jetting process would be relatively slow.
256. Using this basis, the worst case changes in suspended sediment concentrations due to inter-array cable installation are likely to have the following magnitudes of effect (Table 7.19):
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm Chapter 7 Marine Geology, Oceanography and Physical Processes Page 51
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