Testing innovations to enhance nature-inclusive design of offshore wind farms

The Joint-Industry Project (JIP) SPREE (Scour Protection for Ecological Enhancement), funded by TKI Offshore Energy, is a comparative study of armour stone and Engineered Reef Units (ERUS) for scour protection, cable crossings and CPS stabilisation.

A consortium of 12 partners collaborated on the project, including Deltares, Wageningen Marine Research, and Inspire Environmental, a Ventera Group. Innovators such as Reefy, BAM, Holcim, Coastruction, and Geowall contributed technologies and units for testing. Boskalis supported insights into practical installation aspects and LCAs, while RWE, Vattenfall, and TenneT provided insights from an operational perspective.

The SPREE project partners worked together to better understand:

• the technical feasibility of using ERUS as scour and secondary protection for offshore wind farms;
• the potential of ERUS to provide marine habitat and other ecosystem functions in a sustainable manner due to their design, material composition and production method.

Between 2024 - 2025 the SPREE partners investigated the potential use of ERUS as functional protection units through physical testing of their installation and hydraulic stability.

We’re validating whether these ERUSs can function not just as add-ons, but as integrated protective elements. The goal is to assess their performance under hydrodynamic forces and explore their potential to replace conventional materials in coastal infrastructure. This multidisciplinary approach allows us to tackle key questions from various angles

Ioanna Saxoni, researcher and advisor at Deltares

Ioanna Saxoni, researcher and advisor at Deltares explained: “We’re validating whether these ERUSs can function not just as add-ons, but as integrated protective elements. The goal is to assess their performance under hydrodynamic forces and explore their potential to replace conventional materials in coastal infrastructure. This multidisciplinary approach allows us to tackle key questions from various angles,” Saxoni notes. “Ultimately, we aim to offer design recommendations that enable engineers to work with reef units from the start, rather than relying solely on rock-based solutions.”

Hydraulic stability testing of ERUS

The project was structured into four work packages, focussing on: stability, investigating installation feasibility using existing market equipment, life cycle assessments including carbon emissions, and ecological performance.

In work packages 1 and 2 Deltares led the hydraulic stability testing of ERUS in its Atlantic Basin and Scheldt Flume facilities using scale models of the different ERUS designs. The objective is to learn whether the ERUS elements can function as stand-alone protective elements, in the same way as armour stone is currently used or as part of such protective designs, e.g. the top layer of a scour protection. The Deltares team of engineers was supported by colleagues from the consortium partners to conduct this test series.

In total, three test campaigns were conducted, assessing how ERUS compared to conventional armour rock material in terms of their hydraulic stability. The different innovators’ ERUS and armour rock models were used in scaled down layers of scour protection, CPS stabilisation and cable protection around four monopiles in the Deltares test basin.

During the different tests the team alternated design aspects and hydrodynamic conditions for storm conditions representative of storm conditions occurring every 50 to 100 years in the North Sea and the western North Atlantic. Using the resulting measurements, the team was able to assess the deformation occurring and whether or not ERUS could perform as functional protection elements.

The team also assessed the falling behavior of ERUS elements individually and as a group when released into the water column. Together with insights provided by Boskalis, the project thus was able to analyse the feasibility of installing ERUS with conventional fall-pipe vessel installation methods.

Assessing the environmental impact of ERUS

In work package 3, the JIP-SPREE team conducted an LCA (Life Cycle Assessment) to assess the environmental impact of ERUS based on the ‘Milieu Kosten Indicator’ (MKI) and specifically with regards to CO2 emissions. This environmental cost indicator is a single-score indicator that expresses the environmental impact of a product or project in monetary terms (e.g. Euros).

By analysing the required inputs and processes along the different life cycle stages for the two products, the MKI facilitates learning how ERUS compares to armour rock in terms of their environmental impact, especially their CO2 emissions. It further helps to identify optimisation potential for ERUS in terms of environmental impact as their design is further developed to higher technology readiness levels (TRL).

Evaluating nature-inclusive design aspects

Work package 4 was led by Wageningen Marine Research (WMR). In this work package the consortium partners evaluated the nature-inclusive design aspects of ERUS and armour rock by consulting experts for specific taxonomic groups present in the North Sea and western North Atlantic. The evaluation compared different design aspects of ERUS and armour rock in terms of their impact on ecosystem functions (e.g. habitat creation or offering refuge). This evaluation produced location-specific insights into ecosystem enhancement possibilities of ERUS and armour rock.

The work package also engaged experts and stakeholders during an online workshop to generate insights into questions of decommissioning. Specifically, the partners and stakeholders looked into the implications of decommissioning ERUS based on their impact on ecosystem functions. These insights may influence decommissioning policy decision making as well as future research and monitoring of the ecological impact of ERUS.

Ultimately, we aim to offer design recommendations that enable engineers to work with reef units from the start, rather than relying solely on rock-based solutions.

Ioanna Saxoni, researcher and advisor at Deltares

The project results will be shared in a public report by the end of 2025.

Video

Would you like to know more about the JIP-SPREE project? Have a look at this video which provides a short summary and some visual impressions of the work the consortium did.