Assessing the performance of a coupled wave–current model in coral reef systems

• The coupled model reproduces wave spectra, significant wave heights, setup, and currents across complex reef–lagoon topography. • Tidal level is the dominant driver of wave-height fluctuations over the reef flat. • Including tidal currents improves simulated wave-height accuracy by 42 % and contributes 10–23 % of the total variability. • Model performance declines shoreward, highlighting the need for improved low-frequency energy and reflection parameterizations over coral reefs. Numerical simulation using wave–current coupled models is a key approach to investigate the propagation of irregular waves over coral reefs. In this study, a three-dimensional coupled model, developed within a discontinuous Galerkin hydrodynamic framework and a phase-averaged wave module, is applied to evaluate its performance at both laboratory and field scales. In the laboratory reef–lagoon–channel system, the model accurately reproduces wave spectra, significant wave heights, setup, and currents, with high accuracy from the fore reef to the mid-reef flat and slightly reduced performance in the back reef and lagoon. Field applications at the southeastern coast of Hainan Island, China, show that the model effectively captures water levels and wave heights over a continuous five-day period. Compared with measurements, tidal level variation is the primary driver of the simulated wave-height fluctuations over the reef flat, while including tidal currents further improves accuracy by about 42% on average. Tidal level and currents together account for 32–76% of total wave-height variations, with tidal elevation dominating (14–58%) and current effects ranging from 10 to 23%. Near the reef edge, tidal level and current influences are comparable, whereas the tidal level effect becomes up to sixfold stronger shoreward. The combined laboratory and field results suggest that nonstationary wave and tide boundary conditions are more favorable for accurately reproducing wave heights, setup, and currents in the coupled model. Further adding and refining low-frequency wave energy transfer and wave reflection parameterizations will be essential to improve the performance over coral reef coasts.