7.6.2.6 Impact 6: Morphological and sediment transport effects due to cable protection measures for inter-array cables
356. As a worst case scenario it has been assumed that up to 10% of the inter-array cables cannot be buried and must instead be surface-laid and protected in some manner.
357. Cable protection may take the form of concrete mattresses, fronded concrete mattresses, rock dumping, bridging or positioning of gravel bags.
358. The effects that such works may have on marine geology, oceanography and physical processes primarily relate to the potential for interruption of sediment transport processes and the footprint they present on the sea bed.
359. In areas of active sediment transport, any linear protrusion on the sea bed may interrupt bedload sediment transport processes during the operational phase of the proposed project. There is unlikely to be any significant effect on suspended sediment processes since armoured cables or cable protection works would only extend a relatively short distance (up to a maximum of 1m) above the sea bed, except for in areas where the cable crosses other sub-marine infrastructure (e.g. pipelines and cables) where it may extend to a height of up to 4m.
360. The presence and asymmetry of sand waves across around 50% of the sea bed within the East Anglia THREE site indicates that some bedload sediment transport exists, with a net direction towards the north or northeast. There are also sand ridges, megaripples and sand ribbons present.
361. Protrusions from the sea bed are unlikely to significantly affect the migration of sand waves, since their heights would in most areas exceed the height of cable protection works. There may be localised interruptions to bedload transport in other areas, but the gross patterns of bedload transport across the East Anglia THREE site would not be affected significantly.
362. The presence of cable protection works on the sea bed would represent the worst case in terms of a direct ‘loss’ of sea bed area, but this footprint is likely to be lower than that of the foundations (and associated scour hole or scour protection works) within the East Anglia THREE site.
7.6.2.6.1 Assessment of effect magnitude and/or impact significance 363. Taking the aforementioned considerations into account, the worst case changes to the sea bed morphology and sediment transport due to cable protection measures for inter-array cables are likely to have the following magnitudes of effect (Table 7.33):
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm Chapter 7 Marine Geology, Oceanography and Physical Processes Page 71
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