Review of Cabling Techniques and Environmental Effects Applicable
Review of Cabling Techniques and Environmental Effects Applicable
Review of Cabling Techniques and Environmental Effects Applicable
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5.2.2 POTENTIALLY SIGNIFICANT EFFECTS<br />
Seabed disturbance<br />
Potential impacts <strong>and</strong> mitigration measures<br />
Some weeks prior to the installation <strong>of</strong> the cables, a cable burial assessment<br />
survey can be carried out (see previous Section 3.10). Disturbance to the seabed,<br />
leading to an alteration <strong>of</strong> habitat <strong>and</strong> associated species will occur during the<br />
burial assessment survey <strong>and</strong> during cable burial operations. Such impacts are<br />
likely to be limited to an area 2-3m either side <strong>of</strong> the cable, depending upon the<br />
size <strong>of</strong> the installation device used. In general, the range <strong>of</strong> installation devices<br />
available would have similar impact footprints, especially those that are tracked<br />
or have skids in contact with the seabed. Recovery <strong>of</strong> the seabed is, to some<br />
degree, dependent on the substrate that is left following installation.<br />
Certain techniques will aid recovery by infilling the trench following cable<br />
placement. In respect to this potential impact, the action <strong>of</strong> a narrow blade<br />
conventional plough is expected to fulfil this criterion more than any other<br />
method <strong>of</strong> installation. With a narrow blade conventional plough, a wedge <strong>of</strong> soil<br />
is lifted, the cable placed at the base <strong>of</strong> the trench <strong>and</strong> then the displaced soil<br />
wedge is allowed to backfill naturally. Any other excavation method will disturb<br />
the sediment <strong>and</strong> not allow layers <strong>of</strong> sediment to be reinstated in the same<br />
sequence in their natural state. For example, mechanical cutter or jetting systems<br />
have aggressive cutting mechanisms which are used to cut open trenches.<br />
Certain installation devices require the use <strong>of</strong> a vessel that utilises an anchor<br />
array to stabilise the cable laying vessel which would slightly increase the area<br />
<strong>of</strong> disturbance (see Section 3.9.1). As the vessel needs to move as the cable is<br />
laid, anchors are repositioned, increasing the area <strong>of</strong> potential impact.<br />
Where cable crossing (see Section 3.8.6) is necessary there would be a<br />
requirement for the placement <strong>of</strong> cable protection measures such as concrete<br />
mattresses, which would cover a larger area, in the order <strong>of</strong> 150m 2 for each cable<br />
crossing. The exact area would depend on the specified requirements from the<br />
existing cable owner.<br />
Installation <strong>of</strong> cables close to turbine foundations using either ploughs or<br />
remotely controlled tracked vehicles will always result in a short section <strong>of</strong> cable<br />
close to the J-tube exit points not being buried as a consequence <strong>of</strong> limitations<br />
in the cable burial procedure. A common solution for these short lengths <strong>of</strong><br />
exposed cable (typically 10m to 15m) is to use either over covering concrete,<br />
frond mattresses or rock dumping. Rock dumping can be problematic, especially<br />
in <strong>and</strong> around sensitive habitats, as careful placement would be required in<br />
order to avoid unnecessary damage to habitats <strong>and</strong> species. Burial under the<br />
dumped rock would involve a permanent loss <strong>of</strong> habitat where the placement<br />
occurs. These rocks, similarly to all surfaces in contact with the sea, would be<br />
readily colonised by a range <strong>of</strong> fouling species, <strong>and</strong> may act to cause localised<br />
increases in biodiversity. However, artificial increases in biodiversity through the<br />
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