Natural adaptation of atoll islands to sea-level rise offering opportunities for ongoing human occupation (ARISE)

A small team ( Professor Gerd Masselink and Dr Tim Scott ) visited Fongafale, Tuvalu, in March 2025 to do a reconnaissance for a larger field trip in October. They were welcomed by PhD research student Lamese Saamu, who looked after the logistics. Ten atoll islands were visited and seven pressure sensors were installed on the reef platform to start collecting a long-term dataset on inshore waves and water levels. Gerd also gave a talk to the Tuvaluan Lands Department.

The Funafuti islands seem to fall into two categories: small, sandy and rather mobile islands along the less exposed western side of the atoll; and gravelly and relatively static, geologically controlled islands along the more exposed southern and eastern rides of the atoll. Compared to the Maldivian atoll islands, the islands in Funafuti have rich bird life, suggesting that there are no rats on the islands. At the same time, there seems to be much less coral and seagrass in Funafuti.

In April 2025, the ARISE project team attended the Coastal Dynamics Conference held in Aveiro, Portugal, where a series of research projects were presented focusing on coral reef and atoll system dynamics. Topics included coral rubble mobility, nearshore circulation patterns, groundwater dynamics, large-scale hydro- and morphodynamic modelling, wave setup and runup processes, and island typologies for future coastal adaptation strategies.

As part of the conference programme, PhD research student Sam Rose was awarded one of the three best paper awards for the presentation "Measurements of Wave Runup on an Atoll Island Using LiDAR". The ARISE team's strong presence at the conference reinforced the importance of advancing understanding of reef island environments in the context of climate change and sea-level rise.

A subset of instruments remained deployed after the large 2024 field campaign to build a long-term dataset. These sensors were retrieved and redeployed for another year. UAV flights and multibeam surveys were carried out to complete the full digital elevation model. Additionally, ADCP surveys were conducted in the main channel between the islands of Fioyaree and Dighelaabadhoo to get a handle on the tidal currents.

Marine science students from the University of Plymouth were part of the January field trip as part of their degree programme. Thus, research was combined with educational activities to enhance their understanding of coastal processes on atoll islands. Before returning to the UK, Gerd Masselink presented a talk, reporting on the 1 July 2022 island flooding event, to the Maldives National University.

During this campaign, all the instruments deployed over the spring 2024 field trip were recovered. These data are being utilised for various analyses, including tidal fluctuations, sediment transport, groundwater hydrodynamics, wave dynamics and current patterns, and will be fundamental for numerical model development, calibration and validation.

The results from this campaign play a critical component of WP4 stage and serve as baseline datasets for the island. Preliminary outcomes include the development of a detailed digital elevation model and an extensive archived hydrodynamic data set. Results will be presented in April 2025 at the Coastal Dynamics Conference in Aveiro, Portugal. The data will form the basis for much further analysis over 2025 and 2026.

From July to September 2024, extensive physical modelling was conducted in the Delta Flume in the Netherlands, representing WP1 of the ARISE project. A 1:3 scale model of an atoll island with reef platform was constructed and this system was subjected to a range of wave and water level conditions, specifically to investigate how atoll islands respond to sea-level rise.

The tests show that to some degree islands can keep up with rising sea level by increasing their elevation due to overwash-induced sedimentation. As part of the test programme, and in collaboration with Dr Marion Tissier (Technical University Delft) and a Dutch start-up (CoastStruction), the efficiency of artificial reef structures placed on the reef platform, in reducing wave energy at the island shore was also investigated.