Last month RYA reported on the rock placements or rock berms that were put in place to protect the export cables from the Kentish Flats and London Array wind farms at the point at which they cross.
Throughout UK waters cable crossings are becoming more likely, and already more frequent, as offshore energy installations continue to be deployed off coasts. Every energy development has an export cable, or sometimes several, to carry the energy generated ashore.
Impact on navigational safety
Where export cables cross each other in deeper water, they don’t tend to pose a risk to boaters. However, where cables cross in shallower water, the second cable (or set of cables) to be laid often cannot be buried because there are already cables buried beneath them.
Instead, they are laid on the surface of the seabed and protected by rock berms or “mattressing” (flexible concrete slabs). It is this cable protection that in shallow waters can reduce underwater clearance and therefore pose a risk to navigational safety.
Kentish Flats/London Array export cable crossings
The RYA raised the issue of the reduced underwater clearance at the Kentish Flats/London Array export cable crossings at a recent meeting of NOREL – the offshore renewable energy forum. This is because, as a result of the rock berm, underwater clearance has been reduced to less than a metre where the cables cross. The RYA was not aware that the cables would have rock protection until they received a notice.
It would seem that the Marine Management Organisation, Trinity House and the Maritime and Coastguard Agency, were also unaware that the developers were placing a rock berm in this area ‘ and are investigating how all this happened ‘sight unseen’.
Particularly as it seemed that the original London Array Limited applications had stated that the cables would be trenched.
The RYA held a separate meeting with Trinity House regarding the four yellow marking buoys marking the location of the rock berms .
RYA asked that the southernmost yellow special mark be replaced with a South Cardinal buoy as a further aid to navigation for boaters in that area.
Trinity House has since instructed London Array Limited to action this. Trinity House is further negotiating with London Array Limited to establish a mark at the BritNed/London Array cable crossing.
RYA is also making representations to the ‘Examining Authority’ for Kentish Flats Extension (KF2) at the hearings scheduled for May 31st regarding a further cable crossing in the area for the KF2 export cables to shore.
[mappress]
Offshore WIND staff, June 01, 2012; Image: rya