Final UXO (unexploded ordnance) investigations off the coast of Wijk aan Zee have been completed. No ammunition or explosives dating from WOII were found. This means that the export cable laying activities for the wind farms Hollandse Kust (noord) and (west Alpha) offshore connection can start.
This final part of a larger UXO investigation comprised the visual inspection of six (deeper) targets in the coastline. Fugro’s Sea Auk in combination with the WaveWalker1 work platform were mobilised especially for this job. The WaveWalker1 enabled the investigations in the tidal zone. The big advantage of the WaveWalker1 is that its legs are so far apart that when you dig up an object you are not bothered by the slope that forms during the work, says Project manager Koens. These last six targets were quite deep and an excavator could tip over at that slope. This platform can also move itself across the seabed.
Innovative technology
With the Sea Auk, another particularly innovative piece of technology was also applied. “This is a new tool for locating, releasing, identifying and clearing unexploded ordnance in shallow water,” said Koens. “With detection equipment, the tool, which is attached to the end of the crane on the platform, easily locates previously detected targets. Then the team on the platform gets an echo image of the object in the bottom via sonar.”
The Sea Auk also locates deeper targets like these using a magnetometer. Koens: “A water jet in combination with a powerful dredging pump then exposes the object. The team can then identify and inspect the find via the Sea Auk’s camera images.” If it is not a UXO, then the Sea Auk’s large stainless steel claw can bring the object to the surface.”
Finds
A remarkable find is a number of bars of presumably 18th century ‘Swedish steel’ with marks that are now being investigated further. Koens: “The selected finds have been reported in ARCHIS, preserved and presented to the provincial depot in Castricum. Last year, this explosives investigation already yielded two grenades, a 250 lb aerial bomb, an ammunition box, a piece of a mortar and parts of the German coastal defence line; the Atlantikwall. Photo: Chris Pennarts
