Wind farm engineers to drill below cliffs and rivers
- Credit: Supplied by Vattenfall
Energy giant Vattenfall will use a remote controlled drill that will snake its way underground below the fields and cliffs at Happisburgh for one kilometre to a position off the Norfolk shore.
The piece of kit known as a Horizontal Directional Drilling (HDD) rig is a key part of the Swedish firm’s plans to link up to 360 turbines in North Sea wind farms called Vanguard and Boreas to onshore cabling, running to a substation at Necton, near Swaffham.
But although the firm believes its work will not affect Happisburgh’s cliffs - which are eroding at a relatively fast rate - some village residents remain sceptical.
Andrew Hardcastle, the firm's senior project engineer, said they would start by drilling a hole with a narrow diameter and then increase its width.
Mr Hardcastle said: “You start with a very small hole and then you open it up in a stable and controlled manner.
“It’s a technology that was originally pioneered in oil and gas, and we’ll use the same for key features along the route like the River Wensum and River Bure.”
Concerns and questions
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Dave Mole, Happisburgh Parish Council chairman, said that while they understood that scientists and engineers had devised the plans, there were still concerns.
Mr Mole said: “It’s a technical matter and we’re very much in the hands of experts. Our beach is quite delicate and sensitive and we don’t want to make the situation any worse.
“The underground soil is a mixture of clay and sand, and when they push this thing through, it might disrupt those pockets of clay and sand.
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“People have got reservations about it. We just hope it’s successful.”
Mr Mole called on Vattenfall to work with the village to reduce the ongoing erosion there, possibly by contributing to new sea defences.
Malcolm Kerby, from Happisburgh's Coastal Concern Action Group, said he was not worried about the effect of the drilling.
He said: “From my understanding they’re going to drill down and then horizontally, so they’re not going to disturb the cliff at all. I’ve got far greater concerns with the effects of climate change and rising sea levels.”
But Mr Kerby said the wind farms - which will have a planned lifespan of 25 years - would eventually feel the effects of erosion.
How the connection would be made
The drilling will be done from a field around 520m south-east of Happisburgh Lighthouse, where a temporary ‘landfall compound’ will be set up.
Once the hole is drilled a protective pipe, or duct, will be inserted, followed by cabling. After emerging at the seaward end of the duct the cabling will go underneath the seafloor all the way to the wind farms, 47km from the Norfolk coast at their nearest point.
It should take around 20 weeks to install the duct with works scheduled for 2024/25, and another 16 weeks to lay the cable, in two phases in 2026/27.
Vattenfall has said during the first and final weeks of the duct works there would be about three HGVs per hour arriving at the site, and just under one HGV every three hours during the other 18 weeks.
The company carried out some bore hole drilling and offshore surveys last year, but is not planning any further onshore works until 2023.
Catrin Jones, Vattenfall’s stakeholder engagement officer, said they had been working with Felthorpe-based drone firm HexCam carrying out photographic and topological surveys to build a detailed picture of the coastline and how it was retreating due to erosion.
The cabling onshore
Once on land the cabling will run 60km underground to a new substation at Necton.
Ms Jones said only sections of around 150m would be dug up at any one time. She said some sections of hedgerows would have to be removed for the works, but replacement trees would be planted once the cable was in the ground.
She said: “We’re not going to have a massive open trench going across Norfolk because we know that would be disruptive.
“We’re using a ducting technique that minimises the time you’ve got an open trench.
"We’re really aware of how precious hedgerows are and that they’re an important part of the landscape in Norfolk. we’re avoiding hedges with mature trees.”
Although Boreas and Vanguard would share the same cable corridor, a third planned offshore wind farm called Hornsea Three would require another corridor from Weybourne to Swardeston south of Norwich.
Critics have said more cable trenches could follow if further wind farms were built, and called instead for a platform to be built offshore that would link all the stations together before transmitting the power via a single cable corridor across land to the National Grid.
But Vattenfall and Orsted, the firm behind Hornsea Three, have dismissed the idea - known as an Offshore Ring Main or Modular Offshore Grid - as unviable.
Vanguard was approved in July last year, but a judicial review into the decision was later ordered by the High Court, which has not yet been resolved.
The Planning Inspectorate is due to rule on Boreas by April 12.
Vattenfall said Vanguard and Boreas together would be able to power 3.9 million homes.