288. The small increase in offshore cable corridor width along parts of the inshore sections for the proposed East Anglia THREE project when compared against that previously assessed for the proposed East Anglia ONE project does not alter the findings of the previous assessments when applied to the proposed East Anglia THREE project. This is because the increase in sea bed area within the offshore cable corridor is small along the inshore section and the total area of sea bed affected remains an insignificant proportion of the total area of the SPA. Furthermore, the Outer Thames Estuary SPA citation states that the SPA consists of a range of mobile sediments and therefore natural changes in sea bed level would be expected to exceed the predicted effects on a frequent basis.
289. The overall impact of offshore cable installation activities under a worst case scenario on bed level changes for the identified morphological receptor groups is considered to be no impact, except for the ‘Suffolk Natura 2000’ site (in particular parts of the Outer Thames Estuary SPA located within it) which is assessed to experience an impact of negligible significance.
290. In many parts of the offshore cable corridor there would not be the need for release of such volumes of sediment as considered under this worst case scenario, and optimisation of the offshore cable route selection within the corridor, depth and installation methods during detailed design would ensure that impacts are minimised.
291. The effects on sea bed level also 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.
7.6.1.7 Impact 7: Indentations on the sea bed due to installation vessels 292. There is potential for certain vessels used during the installation of the windfarm and offshore cable infrastructure to directly impact the sea bed. This applies for those vessels that utilise jack-up legs or a number of anchors to hold station and to provide stability for a working platform. Where legs or anchors (and associated chains) have been inserted into the sea bed and then removed, there is potential for an indentation proportional to the dimensions of the object to remain. The worst case is considered to correspond to the use of jack-up vessels since the depressions would be greater than the anchor scars.
293. A single jack-up barge leg would have a footprint of 50 to 200m2 and a jack-up vessel would have up to 6 legs. Each leg could penetrate 0.5 to 15m into the sea bed and may be cylindrical, triangular, truss leg or lattice.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm Chapter 7 Marine Geology, Oceanography and Physical Processes Page 58
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