TenneT and Van Oord start research into biodiversity improvement at cable intersections in the North Sea

© TenneT / Van Oord

TenneT will conduct research in collaboration with Van Oord to improve biodiversity at cable intersections in the North Sea. In a pilot project, different types of stone are deposited at cable crossings at twelve locations to investigate which application stimulates biodiversity.

The offshore connection for the Hollandse Kust (zuid) wind farm is the first area to be used as a testing ground. Van Oord recently installed the first two 220 kV subsea cables for the Hollandse Kust Zuid Alpha high-voltage connection for TenneT. At crossings with existing oil and gas pipelines, the cables rise above the sea bed. Here, 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: “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.”

TenneT expects that the calciferous stones will lend themselves well to various benthic species to nest in, so that in time ‘natural reefs’ can arise.

On October 14, the stones were loaded on board Van Oords’ stone dumping vessel Bravenes in Vlissingen. The activities will take place in the coming weeks. In 2021, Van Oord will install the second grid cable connection for Hollandse Kust (zuid) Beta. This connection will involve another six cable intersections.

Jaarsma: “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.”

TenneT aims to apply and monitor nature-reinforcing measures in all its offshore grid projects. TenneT will use the findings of this pilot to assess which measures improve biodiversity.

Earlier this week Van Oord also reported it is taking the next step in another project that involves research into improvement of biodiversity related to offshore wind farms.