Swale export cable installation

We started works to connect the onshore substation at Cleve Hill to the two offshore substations at the wind farm site in 2011.  In total we laid four export cables.  The first cable was installed at the end of 2011, the second installed in early 2012 and the remaining two cables were installed later that year.

The installation of each export cable started in The Swale – as this is a busy area for sailing and shipping activities we worked closely with sea users and the local community to make sure that disruption to planned activities in The Swale was minimised.

In advance of the export cable being installed the route had to be cleared of debris. This was done by a vessel dragging a grapnel hook (a modified anchor which penetrates the seabed) along the seabed. This work was completed in 2011.

Cable installation sequence

The installation of each cable started in the inter-tidal area of The Swale.

• The cable laying vessel (CLV) was moored in The Swale, approximately 1.5-1.8km offshore.
• A winch, installed at the onshore substation site, pulled the cable from the CLV through ductwork already installed under the sea wall.
• The cable was then floated over the mudflats using a buoyancy system.
• Trenches were dug into the mudflats using amphibious excavators. The cables were laid in the trenches and the trenches backfilled.  A displacement burial tool, aboard a small vessel, was used to bury the cable.
• From approximately 2.5km out to the offshore substations the cables were laid and buried simultaneously using a plough deployed on the seabed.

Sea Users Local Liaison Committee (SULLC)

A local liaison group was established with sea users which met on a montly basis. We provided updates and communications, and worked with the SULLC to mitigate the impacts of the cable laying activity on users of The Swale.

Graveney Local Liaison Committee (LLC)

Updates on cable laying activities were given to the LLC which met on a monthly basis. The approved Traffic Management Plan (TMP) remained in force throughout the export cable installation.