The aim of the CREST project is to investigate how reef restoration modifies wave-driven flooding of coral islands under varying sea-levels. This will be done through a series of unique laboratory experiments carried out in the Delta Flume, which is one of the largest wave flumes currently available worldwide. The dimensions of the wave flume will allow the schematization of a coral island at near prototype scale. The island and its (un)restored reef platform will only be scaled down by a geometric factor of 3 (see sketch of the experimental setup fig. 1A). This is about 10 times closer to reality than experiments on reef hydrodynamics done in the past, considerably limiting scale effects. This will not only allow for the first large-scale laboratory quantification of the efficiency of reef restoration as a protection against coastal hazards but will also provide an invaluable dataset for process understanding and prediction tool development.

Coral reef islands are often characterized by maximum elevations of only a few meters above mean sea-level making them extremely vulnerable to coastal flooding. These territories will become even more vulnerable in the future due to sea level rise which is projected to occur at a higher rate in the tropics, increasing the severity and frequency of wave-driven flooding events. Studies have demonstrated it is this increase in the frequency of wave-driven flooding which will first render these islands uninhabitable because of the salinization of the freshwater aquifers they induce. There is thus an urgent need for developing strategies to mitigate wave-induced flooding.

In the first months the focus will be on finalizing the design and planning of the experiments. Because CREST is designed to be highly complementary to the ARISE project, this activity will be carried out in close collaboration with the ARISE team from the University of Plymouth. By doing so, we ensure that the mutual benefits for both projects, and thus for all project partners, are maximised. In this period, the definition of the waves and water level conditions will be finalized for the hydrodynamic runs with and without restoration. The reef structures used to represent the restoration will also be designed. Numerical tests will also be conducted to estimate wave conditions across the reef and provide input for the design of the structures and positioning of the restoration areas on the reef platform.
The experiments themselves will be carried out in the spring of 2024. Two TU Delft MSc students will be recruited and involved in the entire process (Activities 1 and 2). One of these students will be hosted (and primarily supervised) by Deltares, the other one by TUDelft, but all CREST partners will advise the students during the project.

In this project we will conduct the first-ever large-scale experiment investigating the impact of coral reef restoration on wave transformation process across a coral reef platform enabling evaluation of their effectiveness in reducing island flooding. This contrasts with only a handful of earlier small-scale physical experiments where the complex flows associated with 3D coral reef structures cannot be properly simulated. Detailed wave and flow measurements will provide unprecedented insights into wave/reef structure interactions, and as such contribute to the development of engineering guidelines for the deployment of artificial reef structures. The project will furthermore provide an invaluable dataset for numerical model development, contributing to the development of improved forecasting tools for reef-lined coasts and enabling practitioners to analyse future flooding scenarios and optimize the urgently needed risk reduction measures.
A key technical challenge of this project will be the design of a representative coral reef canopy in the lab. Rather than attempting to represent the full structural complexity of a given coral canopy, we will focus on ensuring that the key parameters determining the flow within the canopy, and thus the wave response to the interaction with these elements, are representative of a chosen site. This will be made possible thanks to the use of 3D printing via the collaboration with the startup Coastruction

Product 1: Laboratory dataset including hydrodynamic data with and without reef restoration.
Product 2: MSc theses. The MSc theses will contain a description of the experimental
setup and the first results of the data analysis and modeling.

Accessibility: The data will be made publicly available within a year after the end of the project. This will be
done on the 4TU.ResearchData repository (https://data.4tu.nl/) or an equivalent platform dedicated to
open research data. An accompanying open access data paper will furthermore be published at that
moment. In the meantime, a detailed description of the experiments, analyses and results will be available
in the MSc theses (See Product 2). Before the data is publicly available, the data will be made available to
the project partners upon request.

Press releases will be issued during lab measurements, as well publications on TKI and TU Delft websites during
and after the experiments. These publications will be further advertised on LinkedIn.

Het consortium zal een samenwerkingsovereenkomst sluiten die aan de eisen van de regeling tegemoet komt.