“TenneT is responsible for transporting offshore-generated power to the shore. We manage the offshore grid connections which connect the offshore platforms via cables to the substations on land. If we discover unexploded bombs on our cable route, we either go around them or remove them. The question is: what happens when we go back to carry out repairs? Could the objects along our cable route move? Waves can mobilise and move an object, but this depends on the size of the waves, the depth, weight and size of the object. We developed a numerical model we want to validate in experiments together with Deltares in their flume tank. We have to know how big the risk is and how to eliminate any risk to our people.”

“There are no data about this in the Netherlands, but according to publications here in Germany there are at least 1.6 million tonnes of unexploded ordnances at the bottom of the German sector of the North Sea and the Baltic Sea.”

“I’ve never heard of any fatal incidents in the history of offshore oil and gas platforms, renewable energy installations or communication cables. A few times fishing vessels have accidentally pulled unexploded bombs up onto their deck. It’s a big problem for the environment, but the risk is extremely small for TenneT. Most bombs are clustered in known dump sites, and we intentionally avoid those. The majority of objects we come across are rubbish like bicycles or containers. People have only recently started to consider this risk, since more work is being done at sea due to the construction of offshore wind farms.”

“We asked Deltares to build three concrete and steel models of bombs. I don’t think Deltares would be happy if we put a real bomb in their flume. We generate waves, making them bigger and bigger until the object starts to move. Meanwhile we measure the water velocity and height of the waves, the position of the objects, and whether they’re moving. We need scientific proof for our models and risk assessments instead of just guesses.”