97.
Given the localised and temporary nature of the activities, a negligible impact is predicted on water quality as a result of the proposed landfall works.
8.6.2 Potential Impacts during Operation
8.6.2.1 Impact 1: Deterioration in water quality due to re-suspension of sediments associated with scouring.
98.
The localised changes in the tidal and wave regimes around each foundation structure are likely to result in localised scour of the sea bed. Therefore there is the potential for increased suspended sediment concentrations to impact on marine water and sediment quality. Under a worst case scenario, no scour protection would be used.
99.
In order to undertake an assessment of the potential increase in suspended sediment concentrations as a result of scour around the base of foundations, scour assessments were undertaken (see Chapter 7Marine Geology, Oceanography and Physical Processes and Appendix 7.3 for full details). In summary, the worst case scour volumes are predicted to be considerably less than the worst case volumes of sediment potentially released following sea bed preparation activities and therefore the magnitude of effect would be less.
100. Additionally, given the sediment types prevalent across the East Anglia THREE site, most of the small quantities of sediment released due to scour processes would rapidly settle within a few hundred metres of each foundation. The situation would be similar but with a lower magnitude of effect around any areas of cable protection.
101. Based on this information, the magnitude of effect is assessed as negligible due to the temporary and localised nature of increase in suspended sediment concentrations but also due to the likelihood that any change would be within the limits of natural variation. Overall, therefore an impact of negligible significance is expected.
8.6.2.2 Impact 2: Change in sediment and water quality as a result of the release of hazardous materials, specifically accidental spillages and discharges of grey water.
102. Accidental spillage of lubricants, oils or chemicals during the operational phase may occur directly from wind turbines themselves or from vessels present on site during maintenance activities. In addition to the control measures required under the MARPOL Convention Regulations, standard good practice would be applied as in the East Anglia THREE.
103. As the magnitude of the effect is difficult to assess, the assessment in this instance is considered in terms of the risk of a spill or other accidental pollution event occurring.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 8 Marine Water and Sediment Quality Page 31
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