The Rotterdam Reef pilot used a layered design and flexible monitoring approach to test how well ReefBlocks perform both structurally and ecologically. After baseline surveys in December 2022, the 25-meter reef was installed in March 2023. The blocks were designed with textured surfaces to support species settlement, internal tunnels to improve water flow and shelter, and an overall layout that mimics natural reef shapes.  

Monitoring was carried out for 2 years, with 9 visits using a range of methods. In order to assess the stability and integrity of the structures, the following techniques were used as part of the monitoring program: aerial and underwater drone footage, GPS tracking with total station, and visual surveys. This data is supplemented with annual soil soundings performed by Rijkswaterstaat and post construction bathymetry surveys of Boskalis. The ecological monitoring program aimed to identify species that settle on and around the structure (epifauna), and mobile species that use the structure as permanent or temporal habitat. In order to map mobile species, eDNA samples were taken from both the structure and nearby areas, executed both with manual sampling and with an automatic sampler for 24h. The growth of epifauna and slow-moving organisms (crabs, urchins) was mainly assessed by analyzing camera footage with a focus on succession, growth, and species diversity. Each method was applied at different intervals based on seasonal needs, site conditions, and specific goals, following a flexible monitoring approach.  

Monitoring was adjusted seasonally based on conditions and goals. All results were compared with baseline data from 2022 to understand how biodiversity developed and how the structure held up in the dynamic environment of the Nieuwe Waterweg. 

• Early alignment on roles and expectations was helpful, and for future projects we recommend even more detailed coordination at the start -especially when it comes to linking field activities and partner involvement.
• The flexibility built into the project allowed us to adapt when needed, but clear milestones and regular communication were essential to keeping everything aligned.
• The value of monitoring is greatly improved with an extensive T=0 measurement. A zero measurement has been taken prior to installation of the structure but it deserves recommendation to expand on these measurements to have a better understanding of the results.
• The ReefBlocks remain in place as part of Rijkswaterstaat’s infrastructure, ensuring continued functionality after the pilot phase.
• A logical next step is to apply this nature-inclusive design in larger infrastructure projects, especially where ecological restoration and coastal protection can go hand in hand.
• Reefy is also part of the Joint Industry Project SPREE, which focuses on developing alternatives to scour protection in offshore wind. While The Rotterdam Reef pilot is a separate initiative, the same ReefBlock technology has been tested extensively in offshore conditions, including experiments at Deltares in 2020, 2023, and 2024.