TenneT Starts Project to Diversify Sea Life around Cable Intersections

Dutch transmission system operator TenneT has, in cooperation with Van Oord, started a pilot project designed to improve biodiversity at cable intersections in the North Sea.

The project will see different types of stone deposited at cable intersections to investigate which application best stimulates biodiversity.

The stones will be deposited at twelve sites where the recently laid undersea cable for future wind farms intersects existing oil and gas pipelines.

TenneT is currently working on the high voltage connection for the Hollandse Kust (zuid) wind region. A total of four 220 kV cables will be laid from two transformer platforms, Alpha and Beta, to the Maasvlakte. The first two undersea cables were laid in the last months.

At crossings with the 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.

Saskia Jaarsma, Head Offshore Developments and Large Projects Offshore at TenneT, 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.”

The stones were loaded onto Van Oord’s Bravenes subsea rock installation vessel in Vlissingen on 14 October and will be placed at the cable intersections over the coming weeks.

”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,” said Jaarsma.

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. If so, this would create even larger cavities between the stones, which would make it even more attractive for sea life to nest there,” Jaarsma said.

The Netherlands plans to have 9.6 GW of installed offshore wind capacity by 2030. TenneT, as the Dutch transmission system operator, is responsible for the high voltage connections for offshore wind farms.

The TSO aims to apply nature-reinforcing measures on all future offshore grid projects.