Large-Scale Modelling of Hydro- and Morphodynamics Associated with Reef Platform and Island Systems

Hydro- and morphodynamic processes associated with reef platform and island systems are complex and challenging to measure under the energetic conditions that are commonly associated with significant island change. Numerical models of reef platform hydrodynamics are well developed and widely applied to predict the impact of sea-level rise (SLR) on future flood risk and island habitability. Morphodynamic modelling of atoll island response to SLR is much less well developed, partly due to a lack of suitable observational hydrodynamic and morphological data of island overwash required for developing a robust modelling capability. Hence, such modelling is largely based on uncalibrated models. Here, we describe a large-scale experiment in the Delta Flume where a 1:3 scale reef platform and island system was constructed out of concrete and sand, and subjected to a range of sea-level and wave conditions. It was found that the cross-platform changes in the hydrodynamics (wave energy dissipation, low-frequency wave energy, wave setup, wave runup) were represented very well by the 1D XBeach-NH model. During physical model simulations with SLR, the island was found to more or less keep pace with the rising sea level through overwash-induced deposition.