A £625m project to connect the energy systems of the UK and Belgium has unearthed more than a dozen bombs and mines dating back a century to when the continent was racked by war.
Detailed underwater surveys by National Grid, undertaken this year ahead of the laying of the 80-mile interconnector, have detected 19 pieces of unexploded ordnance from the first and second world wars along the seabed on the planned route.
The finds highlight the unique challenge of running a power cable in one of the world’s busiest shipping lanes, with a history of such intense warfare.
“It’s mines normally, sometimes bombs dropped from aircraft, some are from the first world war. You find mines that are attached to the seabed still, mines that are floating around,” said Mike Elmer, the project director for Nemo Link.
The firm and its Belgian partner have had to call in the Royal Navy, and the Belgian and French navies, to explode the bombs and sea mines – usually a much safer option than removing them.
The ordnance is clustered nearest the UK and Belgian shores, mostly found in seas 10-15 metres deep, meaning navy divers have to navigate murky waters to attach explosives and detonate the unexploded bombs. In some cases, remotely operated vehicles (ROVs) have also been deployed to explode the ordnance.
The largest find was a huge, two-tonne bomb believed to have been dropped by the US airforce, and probably used to destroy concrete bunkers. It was detonated by the Belgian navy earlier in July. The last few pieces of unexploded ordnance are all in Belgian waters.
Petty Officer Scotty Eaton, a Royal Navy diver who tackled one of the sea mines recently, said that a four-strong team would first send a diver down to confirm the ordnance, before alerting the coastguard to establish a shipping cordon.
PE8 explosives are then attached to the bomb or mine, with the detonation initiated from the surface. “The biggest challenge we found ... was the tides, they are unpredictable,” Eaton said. Rising tides increased the risk of a diver becoming entangled in their guide line and the detonating cord.
Other discoveries in the underwater mapping, undertaken by vessels trailing hi-tech sensors through the water, include a cannon, cannonballs, and an anchor.
While the interconnector route has remained largely unchanged by the finds, it was rerouted after pieces of an aircraft wing were found, thought to be from the second world war. As a potential war grave, a 100-metre exclusion zone was ordered.
Elmer said the biggest threat to potentially delaying the project had come not from bombs, but a 14th-century ship found in French waters.
“It’s off the route, fortunately, because that would have delayed [the project]. That’s being treated by the French government as archaeology, and as soon as they designate as archaeology, a 100-metre exclusion zone is put through the whole thing,” he said.
After works started in October 2015, Nemo Link is now around halfway through construction, and due to be operational in January 2019. It will come onshore near Sandwich in Kent, and Zeebrugge in Belgium.
There are four such UK interconnectors at present. At least a further eight, including the one to Belgium, are being laid along the seabed or through the Channel Tunnel in one case, to exchange power between the UK, Ireland, Denmark and Norway.
As Britain generates a growing share of electricity from intermittent sources such as windfarms and solar panels, the cables have become increasingly important, providing around 7% of power. They also help dampen down peaks in wholesale prices.
One thinktank recently warned that Brexit could put new projects at risk, with a knock-on effect on energy bills. “Electricity interconnection with the EU meets 7% of UK’s electricity needs and keeps consumer energy bills down,” the Green Alliance said.
Elmer said that even with the UK leaving the EU, the case for greater interconnection is as important. “Brexit is a complication, it would be foolish to deny it. But we still need to trade power,” he said.