Dutch-German grid operator TenneT has started a pilot to improve biodiversity at cable intersections for offshore wind farms in the North Sea.
TenneT is working on the project with offshore contractor Van Oord.
The pilot will involve depositing different types of stone at cable intersections to investigate which application best stimulates biodiversity.
TenneT said it aims to apply and monitor nature-reinforcing measures in all its offshore grid projects. TenneT will use the findings of this pilot, which features 12 sites, to assess which measures improve biodiversity.
In the North Sea, TenneT is working on the high voltage connection for the Hollandse Kust (zuid) wind region.
Four 220 kV cables will be laid from two transformer platforms (Alpha and Beta) to the Maasvlakte.
The first two undersea cables were laid recently. At crossings with existing oil and gas pipeline, the cables rise above the seabed.
At these sites, a granite top layer is deposited on top of the cable to protect it.
TenneT offshore developments head Saskia Jaarsma said: “TenneT is starting a pilot in which, in close cooperation with Van Oord, it will replace the granite top layer at three cable intersections with a calciferous stone originating from a marble quarry.
“The small calciferous stones will be applied to a total of three of the six intersections.
“This will enable us to assess the difference in the type of sea life that will emerge at these intersections in comparison to the intersections without small calciferous stones.”
On 14 October, the stones were loaded onto Van Oord’s Bravenes subsea rock installation vessel in Vlissingen and will be placed at the cable intersections over the coming weeks.
Jaarsma added: “Our expectation is that the calciferous stones will ensure that various benthic species will find it easier to nest here and that a different habitat will emerge at these sites.
“Over the years, ‘artificial reefs’ can emerge at these sites in the North Sea, where plants and small creatures can settle.”
In 2021, Van Oord will install the second grid cable connection for Hollandse Kust (zuid) Beta. This connection will involve another six cable intersections.
Prior to the installation of this connection, TenneT wants to investigate whether it is feasible to fully remove the existing protective top layer of granite.
Jaarsma said: “If so, this would create even larger cavities between the stones, which would make it even more attractive for sea life to nest there.”