Process-based numerical modeling of reef island morphodynamics has significant potential to enhance our understanding atoll island vulnerability and adaptation to future sea-level rise (SLR). However, limitations associated with traditional numerical models and a lack of available benchmarking data have prevented detailed morphodynamic modeling in reef environments, to date. Here, we apply XBeach-G (non-hydrostatic) to represent sediment transport and morpho-dynamic change on a gravel Motu in Tuvalu. Scaled physical modeling experiments were used to comprehensively analyse model behavior and sensitivity to grain size, ground water conductivity and Nielsen’s phase angle, with multiple combinations producing a close match with wave flume results. XBeach-G was then used to explore island morphological adjustment to SLR, highlighting the complexity and potential associated with representing decadal-scale change in a phase-resoling model. Outputs suggest that island crests can accrete vertically at a similar magnitude to SLR if a near-equilibrium morphology is maintained.
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