The Netherlands EcoScour – Eco-Friendly Scour Protection at the Borssele Offshore Wind Farm (Site V)

Photos
Left: Deployment of oyster broodstock structure in OWF Borssele V.
Right: Baskets filled with different substrates to test suitability for oyster larvae settlement in Lake Grevelingen.

Sea basin:	North Sea
Country:	The Netherlands
Coordinates:	51°43′N 3°00′E / 51.72°N 3°E
Target species:	European flat oysters
Implementation period:	2019 – ongoing
Implemented by:	Van Oord, Wageningen Marine Research, Waardenburg Ecology, Netherlands Institute for Sea Research, HZ University of Applied Sciences, Roem van Yerseke
Type of infrastructure:	NID scour protection in bottom fix offshore wind farm.
Funding:	Two Towers
About:	The Borssele Offshore Wind Farm (site V) is located 22 km away from the Dutch coast. Its purpose is to test innovative design technologies and comprises 2 wind turbines with a total installed capacity of 18 MW.

Objectives:

The project aims to enhance natural habitats in offshore wind farms, with a particular focus on the European flat oyster by developing and testing various eco-friendly scour protection designs and oyster reinstatement methods.

Short description:

In 2019 a pilot project was launched at the Borssele Offshore Wind Farm (Site V) in the Netherlands, designated as a testing site for innovative technologies, including methods for the enhancement of ecological components. Scour protection is usually installed at the base of offshore wind turbines to stabilise the foundations and protect the seabed against erosion. This project developed and studied different scour protection materials aimed at enhancing marine life within offshore wind farms. Materials such as granite, marble and concrete were tested to encourage the settlement of flat oyster (Ostrea edulis) spat in an oyster pond in Ireland, at nearshore areas in Ireland (Tralee Bay), and in the Netherlands (Lake Grevelingen). Additionally, broodstock structures were designed and placed on the scour protection in the Borssele wind farm Site V to establish local larvae production and initiate the oyster reef development. Spat on shell was also deployed in cages. The native oysters used in the project were sourced from a disease-free area in Ireland, and researchers ensured that no invasive species were present before introducing them to the test site. This methodology for procuring and placing oysters in scour protection has provided valuable insights for future oyster reef restoration projects.

Project results:

Monitoring of the experiments in the wind farm involved lifting structures from the sea, collecting samples on the vessel, and sending them to laboratories for detailed analysis. ROV footage was also captured during the lifting process. So far, vertical surfaces on broodstock structures have shown better oyster survival rate, while horizontal surfaces have experienced sedimentation. Squared heavy broodstock structures were considered less optimal due to their weight and the risks posed to installation vessels for their pointed edges. The next phase of the project will focus on using lighter and smoother structures. Adult broodstock was observed to grow and reproduce, and spat on shell has exhibited growth. The best settlement substrate for oyster larvae was granite (Ter Hofstede at al., 2024). Tests with different rock materials indicate that the use of a mixture of scour rock material could enhance the functional diversity of the benthic fauna (Kingma et al., 2024). The project monitoring is set to end in 2028, and the broodstock structures will then be decommissioned.

References:

Ter Hofstede R, S Witte, P Kamermans, L Tonk (2024), ‘Settlement success of European flat oyster (Ostrea edulis) on different types of hard substrate to support reef development in offshore wind farms’, Ecological Engineering Vol. 200, available here:
https://doi.org/10.1016/j.ecoleng.2024.107189

Kingma EM, ter Hofstede R, Kardinaal E, Bakker R, Bittner O, van der Weide B, Coolen JWP (2024) ‘Guardians of the Seabed: Nature inclusive design of scour protection in offshore windfarms enhances benthic diversity’. Journal of Sea Research 199:102502.
https://doi.org/10.1016/j.seares.2024.102502

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