DEM North Sea

The Digitalisering Ecologische Monitoring (DEM) project aims to provide an impulse for the development of new techniques, sensors, and gathering of ecological data on the functioning of the North Sea ecosystem. The ecological data will mostly be gathered through the deployment of 17 different sensors at various locations on the Dutch Continental Shelf (DCS) of the North Sea. It is foreseen to deploy these sensors on string buoys and ecology buoys, which will be located at predefined locations. Originally, it was foreseen to place buoys at locations Terschelling 135, Noordwijk 10, Walcheren 20 and Duitse Bocht. After comparing different scenarios and gathering advice from involved experts, Rijkswaterstaat opts for continuous measurements at two locations: Terschelling 135 and Noordwijk 10. The collected data are ultimately intended to be used for the calibration and validation of models and for ecosystem analyses of the North Sea. In the first half of 2025, Deltares was asked by Rijkswaterstaat to provide a general overview of how the different parameters can ultimately find their way into the above-mentioned applications. The results of this precursor study can be found in the Deltares report by Hendriks, Blauw and Stolte (2025). The work described in this report builds upon this earlier work and is divided into four work packages (WPs), each with their own set of questions. For these questions Rijkswaterstaat (RWS) wishes to receive insight into the desired (end) situation, as well as how project DEM relates to both Dutch and international best practices. For each WP, we have summarized the main take-away messages below: 1. Advice on data collection The originally foreseen locations for the buoys (Terschelling 135, Noordwijk 10, Walcheren 20 and Duitse Bocht) all lie in distinctly different hydrodynamic and ecological settings. After analysing existing measurement data, we provided advice on the ideal height for each of the four instrument sets at the currently foreseen locations Terschelling135 and Noordwijk10. Stratification strength, pycnocline depth, light extinction and gradients near the seabed – especially relevant for suspended sediment and oxygen – are important to consider for placing the sensors in such a way that they provide meaningful data. Additionally, we examined the required calibration and validation steps for the STAF, ADCP, FCM, HSR and PAR instruments (for an overview of these terms please see Section 0). These steps should be performed pre- and post-deployment. As calibration, validation and QC/QA (Quality Control and Assurance) are three crucial steps in the pipeline of a successful monitoring system, they must be undertaken with care and precision to ensure highest possible accuracy of data records and reduction of uncertainties. Furthermore, we advise to leverage MWTL measurements taken at Terschelling 135 and Noordwijk 10 for reference measurements of the different instruments. 2. Advice on data processing, management and usage We advised on workflows to go from raw to usable data and specifically looked at five instruments: STAF, ADCP, FCM, HSR and PAR. Each of the considered instruments has its own specific workflow how to get from raw to usable data. The level of automation and availability of accessible scripts also varies considerably for the different instruments. Best practices to be aware of are: (1) Developing and maintaining scripts are two specialized tasks, and both require the right skills and infrastructure. This is especially the case for the suite of specialized instruments that will be installed on the DEM buoys. (2) It is preferable to build on open-source software/toolkits. However, before choosing a repository, it would be good to check under which license it is distributed and whether it is actively maintained. (3) Apart from automated QC procedures, we advise to include a visual inspection by the expert group (or similar specialists) as part of the quality control protocol, especially in the buoy testing phase. 3. Formation and implementation of expert group An expert group has been formed, which will advise the DEM project team on content-related matters. For this expert group, we have developed an implementation plan. We can discern between three main phases for project DEM, and the role of the expert group evolves throughout these phases: 2025: Preparatory phase 2026: Design, Build and Test phase 2027-2028: Operational phase 4. Compliance with JERICO The DEM buoy network will be one of many observation activities in the North Sea. The DEM data are most useful if their observation strategy is well aligned with these other activities. To achieve this, collaboration and alignment activities are needed both at the national and international level. We aim to integrate the DEM buoys in the international JERICO research infrastructure. Within the DEM project we plan to develop the national research infrastructure for coastal observations and collaborate and align DEM activities during the further development of the European JERICO research infrastructure. Overall, substantial progress has been made within project DEM in 2025 and the collaboration between Rijkswaterstaat and Deltares took place in good harmony. We look forward to 2026, when we expect to continue our work on the different topics within the framework of SITO-PS.