Impact
Key design parameters forming the worst case scenario 31,000,000m3 of sediment.
The maximum realistic speed of cable installation is likely to be approximately 450/hr.
Rationale
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: Re-mobilisation of contaminated sediments
Impact 4: Underwater noise and vibration
Operation
Impact 1: Permanent Habitat Loss
The maximum possible sea bed footprint of the project including scour protection. The scour assessment Appendix 7.3 shows that the maximum scour holes would be smaller than the maximum area of scour protection as specified in Chapter 5 Description of the Development. The size of footprint is based on the following:
1. 60m gravity base foundations and scour protection calculated as 25,500m2 per foundation (see Chapter 7 Marine Geology, Oceanography and physical processes Table 7.4). Therefore for 106 foundations (see Rationale column) the maximum area of disturbance would be 2.71km2. 2. The gravity base foundation and scour protection footprint for two
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
The scenario described gives rise to the greatest area of permanent sea bed habitat loss. Areas impacted by scour would be changed irreversibly and would therefore count as habitat loss, however it has been shown in Chapter 7 Marine Geology, Oceanography and Physical Processes that the area taken by scour protection is likely to be larger than the areas which would experience scour apart from in water depths less than 15m.
It is expected that any requirement for cable protection
Chapter 10 Benthic Ecology Page 11
As Above Installation of 2 monopiles at a time using hammer energies of up to 3,500KJ
The worst case would involve the maximum amount of suspended sediment released into the water column. This is calculated in the row above.
The greatest impact to underwater noise, which may affect benthic species, would be from installation of monopile foundations. The hammer energies used relate directly to the amount of underwater noise produced.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104