Coral atoll islands, common in (sub)tropical oceans, consist of low‐lying accumulations of carbonate sediment produced by fringing coral reef systems and are of great socio‐economic and ecological importance. Previous studies have predicted that many atoll islands will become uninhabitable before the end of this century due to sea level rise exacerbating wave‐driven flooding. However, the assumption that such islands are morphologically static has been challenged by observations and modeling that show the potential for overwashing and sediment deposition to maintain island freeboard. Reliable long‐term predictions of island change and future flood risk, essential for adaptation planning, are, however, lacking. Here, we adopt a novel, efficient approach for modeling the long‐term island response and illustrate the morphological response of an atoll island to future sea level rise and the effect of various adaptation measures. We demonstrate that wave‐driven sediment deposition increases island (beach) crest freeboard. We find that the assumption of static island morphology leads to a significant increase in the predicted frequency of future island flooding compared to morphodynamically active islands. Reef adaptation measures were shown to modify the inshore wave energy, influencing the equilibrium island crest height and therefore the long‐term morphological response of the island, while beach restoration mainly delays the island's response. Accounting for long‐term natural island dynamics, including the morphodynamic feedback from adaptation measures, offers more realistic projections of future flood risk compared to current static island model predictions. These local projections of island response can serve as decision support tools for climate adaptation.

The emerging global wave energy industry has the potential to contribute to the world’s energy needs, but careful consideration of potential impacts to coastal processes in the form of an impact assessment is required for each new wave energy site. Methods for conducting a coastal processes impact assessment for wave energy arrays vary considerably in the scientific literature, particularly with respect to characterising the energy absorption of a wave energy converter (WEC) array in a wave model. In this paper, modelling methods used in the scientific literature to study wave farm impacts on coastal processes are reviewed, with the aim of determining modelling guidance for impact assessments. Effects on wave climate, beach morphology, and the surfing resource for coastal water users are considered. A novel parameterisation for the WEC array transmission coefficient is presented that, for the first time, uses the permitted power rating of the wave farm, which is usually well defined at the impact assessment stage, to estimate the maximum likely absorption of a permitted WEC array. A coastal processes impact assessment case study from a wave farm in south-west Ireland is used to illustrate the application of the reviewed methods, and demonstrates that using the new ‘rated power transmission coefficient’ rather than a WEC-derived transmission coefficient or complete energy absorption scenario can make the difference between significant and non-significant levels of coastal impacts being predicted.