On 12 March, SeaTerra detonated the last buoyant mine found at the Trianel Windpark Borkum II (TWB II) site as part of an unexploded ordnance (UXO) campaign that had been running over the recent months, thus marking the completion of the project.
As part of the required UXO survey and target investigation, SeaTerra identified eleven major UXO targets, including seven buoyant mines, two ground mines, one depth charge and one bomb.
The ordnance targets were not transportable, so the company’s explosives specialists and ordnance divers had to demolish them in situ. All demolitions were thoroughly prepared and designed in close cooperation with the responsible regulators, and marine mammals protected by scaring devices and a “Big Bubble Curtain” to minimise noise, SeaTerra pointed out.
Prior to the ordnance clearance works, the company performed comprehensive geophysical surveys across 427 hectares of the seabed, covering wind turbine locations, infield cable routes and anchor areas. The surveys had been carried out with high-resolution magnetometers utilising array systems (ROTV) or remote operated vehicles (ROV). Subsequent data interpretation led to the identification of hundreds of anomalies, of which SeaTerra identified 288 as potentially dangerous objects, which were then investigated and cleared with the help of remote-controlled devices (ROV, airlift), cranes and ordnance divers.
For the UXO campaign at TWB II, SeaTerra used the vessels Mimer (ROTV survey), Vos Star (ROV survey and target investigation) and Olympic Challenger (target investigation).
The construction of TWB II is expected to start soon at the project site approximately 40 kilometres north of the island of Borkum, within the German sector of the North Sea. The wind farm’s 32 Senvion 6.2M152 turbines are scheduled to be connected to the grid by the end of 2019.