Numerical simulations of breaking wave propagation through the vegetation on a slope based on a drag coefficient prediction model

Coastal vegetation plays a key role in wave attenuation on sloping beaches. However, accurately predicting the vegetation-related drag coefficient (C-D) under breaking waves on slopes remains a challenge. In this study, the Reynolds-averaged Navier-Stokes equations were modified by incorporating a vegetation resistance term to consider the vegetation-induced momentum loss. The stabilized k-omega shear stress transport turbulence model was improved by introducing the vegetation-induced turbulence generation and dissipation terms. The numerical model was validated by two laboratory experiments. Based on experimental wave height data, the C-D was determined via a calibration method. The numerical results were found to be highly sensitive to the C-D. The calibrated C-D achieved excellent agreement with experimental data (RMSE < 0.2). In addition, the calibrated C-D showed a high correlation (R-2 = 0.85) with the Iribarren number xi. Finally, a C-D prediction formula expressed by the combination of Reynolds number and xi was proposed via regression analysis, and its performance was evaluated by two additional cases. The limitations and applicability of the C-D prediction formula were also discussed. The proposed numerical model and C-D prediction formula have the potential to be useful for the numerical simulation of wave interactions with vegetation on slopes.