Numerical Investigation of Irregular Waves and Induced Currents in the Modaomen, Pearl River Estuary

The Modaomen Estuary has evolved from a runoff-dominated to runoff-and-wave-dominated estuary; thus, waves have become an important dynamic force. However, the nearshore irregular waves and wave-induced currents in the Modaomen Estuary have not been well studied. For the first time, a coupled wave-current model was developed in which the wave properties were calculated by the hyperbolic mild-slope equation, and the flow motion was simulated using a depth-averaged shallow water equation that was modified by introducing wave radiation stresses. The computational capability of this model was well calibrated by laboratory data from published references. Subsequently, the validated model was employed to analyze the wave height distributions, flow field characteristics and residual current under irregular waves, as well as to determine the differences in the above results with the scenarios under pure wave or pure tide. The results showed that the irregular wave heights reach 0.75 m near the sand bar and its surrounding shoals, reach 0.7 m in the main channel, and are approximately 0.3 m in the wave shadow area behind the Sisha shoal, which is more powerful than that under regular waves. The effect of waves on the current at the maximum ebb tide is greater than that at the maximum flood tide, especially in the estuarine shoal zone. Compared with the current velocity under pure tide, the residual current velocity is larger, and the vortex scale and the sediment transport route are all prominent under the combined wave and tide.