Beach Works and Bringing the Windfarm Cable to Shore

Beach Works and Bringing the Windfarm Cable to Shore

The cable connecting part of the Walney Offshore Windfarm to land was delivered to Cleveleys on 8 May 2011. It runs along the beach from the seafront, right out to the windfarm at sea.

​Works began at the beach on North/Rossall Promenade in mid March 2011 in preparation for the arrival of the submarine cable. The cables in the highway were previously installed by a landfall team. They end in a joint bay on Thornton Gate, just where it turns the corner from North Promenade.

A separate offshore team were responsible for installing the cable to low water mark. This article describes the bit in the middle, the landfall interface, and how it was managed.

Beach Works and Bringing the Cable to Shore

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The project team had originally intended to drill from the beach to the excavation pit at Thornton Gate. For a variety of reasons, this plan was changed to an open-cut method where the ducts were laid in a trench across the road. It was possible to auger-bore under the actual walls themselves, to minimise disturbance in the area. Most of the technical reasons for this change were to do with future-proofing the safety of the cable. Particularly if any work is done in the future to rebuild this bit of the sea defences.

Working on the Beach

To carry out work in the tidal area of the beach, a long, narrow cofferdam was built. A cofferdam is a an enclosure built in the water to allow the enclosed area to be pumped out. This creates a dry area for work to be carried out.

Sheet piling at Rossall Beach to build the cofferdam for the cable to the windfarm
Sheet piling begins at Rossall Beach to build the cofferdam for the cable to the windfarm

In case you’re wondering how they get those long lengths of metal piles  to line up accurately, here’s a clip of how it’s done!

Positioning piles ready for installation, at Rossall Beach Cleveleys

Then they’re vibrated down into the beach with the piling rig, which you can see in the next photo –

Sheet piling at Rossall Beach to build the cofferdam for the cable to the windfarm

The cofferdam extended from the low re-curve sea wall, quite someway out into the beach.

Looking into the cofferdam at Rossall Beach, built to allow the cable from the windfarm to be connected to land
Looking into the cofferdam at Rossall Beach, built to allow the cable from the windfarm to be connected to land

Spanning the Sea Wall

One lane of traffic was closed at a time while a concrete cased steel pipe was fitted from the excavation pit at Thornton Gate. It goes under the sea walls and promenade, down the beach to where the new design finishes. The cable is protected by the concrete casing so there’s no possibility of disturbing it in years to come. You can see the steel pipe in this photo –

Steel pipe being installed in the cofferdam
Steel pipe being installed in the cofferdam

When the work was finished, all of the lengths of steel making up the cofferdam were removed from the beach. All except the central few which are joined to the block of concrete with the steel pipe going through them. You can see them in the photo above. They were installed at a low level, but you can sometimes see the top of them when the beach drops to its lowest levels after bad weather. Look on the beach opposite the end of Thornton Gate.

Remains of the end of the cofferdam at Rossall Beach Cleveleys
Remains of the end of the cofferdam at Rossall Beach Cleveleys

Crossing the Beach

Plastic cable ducts were next pulled back through the steel pipe all the way to Thornton Gate. They form a continuous sealed duct for the cable to be pulled through. The ducts extend from the seaward end of the steel pipe, buried deep in the beach, right out to low water mark.

All of the preparatory work had to be done before the cable could be pulled to land from the windfarm. Of course another, huge piece of work was being done meanwhile out at sea, to install the turbines themselves.

Installation of the cable in the beach is a fascinating process for anyone lucky enough to see it. It’s not every day that you see a great big ship parked on your beach! The Stemat Spirit cable laying barge was first seen just offshore in the afternoon of Saturday 7 May 2011.

The Stemat Spirit cable barge at anchor offshore, the day before the cable pull operation
The Stemat Spirit cable barge at anchor offshore, the day before the cable pull operation

Arrival of the cable barge on Cleveleys beach

The ship anchored on the high tide in the early hours of Sunday morning of 8 May 2011. At very low tide it was left sat on the beach. At about 9am on Sunday, the crew was mobilised and the process of pulling the cable from the huge spool on board the barge began.

Here are some photos of the works.

The cable barge lined up with the marker buoys. See how close it came to shore.
The cable barge lined up with the markers. See how close it came to shore.
The Stemat Spirit cable barge beached on shore, with the cable pulling in operation
The Stemat Spirit cable barge beached on shore

The High Voltage Electricity Cable

A plough attached to the barge had already carved a 2m deep trench into the seabed. The high voltage cable was unrolled off huge spools on the back of the ship and dropped into the trench to be covered in sand.

The marine cable is one piece from the windfarm to land. It’s an armoured, high voltage 132kv power cable, complete with a 48 core fibre optic cable which provides communication to the windfarm.

Launching the cable off the ship into the ducting
Launching the cable off the ship into the ducting
Launching the cable from the ship into the ducting
Launching the cable from the ship into the ducting
The Stemat Spirit cable barge beached on shore
The Stemat Spirit cable barge beached on shore. The digger is pulling the cable into the ducting.
The Stemat Spirit cable barge beached on shore, with the cable pulling in operation
The Stemat Spirit cable barge beached on shore, with the cable pulling in operation. See the drum of black and yellow cable on the boat.

Here’s a video showing some of the process. Although it was only 2011 it was shot on a compact camera, before the days of smartphones. The quality of the film isn’t very good!

Pulling the cable for the Walney Offshore windfarm off the cable barge at Cleveleys

Joining the Windfarm Cable to Land

During the previous months, a cable had already been laid in the highway. It runs from the joint bay at Thornton Gate, across the tramway and Amounderness Way to Fleetwood Road North. From there it goes along Trunnah Road to Hillhouse Industrial Estate. It delivers the electricity through a brand new substation and into the National Grid at Stanah.

The next task on cable laying day was to get the cable which was pulled off the barge to meet the cable which had been laid in the road.

Where the landfall and beach cables for the windfarm meet, at the joint bay on Thornton Gate
Where the landfall and beach cables for the windfarm meet, at the joint bay on Thornton Gate

Actually joining the two cables together is quite a technical and specialist piece of work. That was carried out a few weeks later by a team of electrical engineers who are specially trained in this work.

Finally, at the end of a long and tiring but successful day, the Stemat Spirit cable laying barge sailed off into the sunset

Stemat Spirit cable laying barge sailing away at the end of the day
Stemat Spirit cable laying barge sailing away at the end of the day

Find out More

Visit Fylde Coast worked with DONG Energy throughout the duration of this project. We provided updates and information for the public and residents along the route in a portal on the Visit Cleveleys website. In addition there were letter drops, public meetings and more.

Most of it hasn’t been updated as we’ve upgraded the website from version to version, so some of it may be askew. But you’re very welcome to have a look if you’re interested. There’s much more in this section about the Walney Offshore Windfarm.

While you’re here…

Have a look at the homepage of the Visit Cleveleys website for more of the latest updates.

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