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Impact


Worst case parameter for assessment


years with a maximum of two sea bed preparations for foundations per day.


The maximum cable installations within the offshore cable corridor includes the installation of up to 620km of HVDC export cable, which would result in the disturbance of up to 31,000,000m3 of sediment.


The maximum realistic speed of cable installation is likely to be approximately 450/hr


Rationale


be more widely dispersed by tidal currents. However the volumes involved are far smaller than sea bed preparation for gravity base foundations (Chapter 7 Marine Geology, Oceanography and physical processes Table 7.5) and therefore overall it is considered that installation of gravity base foundations are the worst case scenario for re-suspension of sediments.


The sediment disturbance during cable installation takes a very conservative approach assuming that all cable trenches would measure 5m depth by 10m width as those are the maximum possible dimensions (Chapter 5 Description of the Development). In reality, trenches would be V shaped and therefore less sediment would be disturbed.


Impact 3: Underwater noise Spatial worst case Monopiles:


1. Up to two concurrent piling events 12m diameter piles 3,500kJ hammer


Temporal worst case Jackets:


2. No concurrent piling 172  7MW devises, and 8 offshore platforms, 1,800kJ hammer


3. Duration of pile driving within construction period is two years. 4. Total piling time 1,032 hours jackets and 408 hours and 36 minutes monopoles


5. Maximum distance between piling events is 33.2km. 6. Maximum number of concurrent piling events is two. 7. Maximum of two vessel movements per day. 8. Max number of vessel movements= 5,700


Installation of monopile foundations for wind turbines/met masts and tubular jackets and piles for the accommodation/electrical platforms would result in the greatest associated noise impact ranges. Alternative infrastructure options (eg. tubular jackets and piles for wind turbines) would result in a smaller noise impact range but would also involve a greater number of piling events over a longer period of time. The worst case scenario considers that the maximum noise range disturbance from construction noise (i.e. maximum spatial effects) has a greater effect on fish and shellfish than the effect of temporal disturbance (i.e. maximum duration)


Preliminary Environmental Information May 2014


East Anglia THREE Offshore Windfarm


Chapter 11 Fish and Shellfish Page 14


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