197. Also, 250m minimum outer protection buffer areas at each side of the corridor are required.
5.4.11.9 Export and interconnection cables: disturbance and displacement. 198. It has been estimated the cable installation process could create a maximum trench width of up to 10m, in order to achieve 5m deep burial of cables.
199. There would be material displaced by the presence of the cable, however this would be minimised as the trench would be backfilled with its own material.
200. Some material may be displaced before cable-laying if rocks need to be moved from the route corridor or if the sea bed needs to be levelled by dredging in areas with high and steep sand waves.
5.4.11.10 Export and interconnection cables: jointing infrastructure
201. The jointing of sub-sea cables offshore would require a significant good weather time window. Typically the jointing can take between one and ten days after both cable ends are secured on-board the jointing vessel. Additional time is needed to recover the cables pre-jointing and rebury the cable post-jointing.
5.4.11.11 Export and interconnection cables: cable and pipelines crossings.
202. There are several existing cables and a pipeline within the offshore cable corridor (see Chapter 18 Infrastructure and Other Users for details). Each crossing requires a cable crossing agreement signed between the owners.
203. Where the offshore cable is required to cross an obstacle such as an existing gas pipeline or communications cables, the additional protection elements may be employed to protect the obstacle being crossed. Once protection is in place it would not be possible to bury the cable being laid leaving it more susceptible to external damage. To mitigate this further protection would be required.
204. For a typical pipeline or cable crossing a concrete mattress would be employed with typical dimensions of 6m long by 3m wide by 0.3mhigh. The number of mattresses required would depend on the size, type and vertical position of the asset to be crossed, the number of cables crossing and the separation of the cables that can be achieved at the point of the crossing. An alternative may be a bespoke designed concrete bridge which is installed over the existing pipeline or cable with the offshore export cable being installed perpendicular, over the bridge. A substitute to concrete mattresses may involve rock filter bags laid over the existing obstacle.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 5 Description of the Development Page 46
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