Effects of wave-current interaction on the Pearl River Estuary during Typhoon Hato

The response of the Pearl River Estuary (PRE) to Typhoon Hato (2017) and the effects of wave-current interaction (WCI) are evaluated by a three-dimensional wave-current coupling hydrodynamic model (COAWST). Typhoon Hato is one of the strongest tropical cyclones in over 7 decades: it struck southern China and caused immense destruction. Our model results show that the maximum storm surge near the western shore of the PRE increased by 20%-30% due to WCI effects. Moreover, both the tidally averaged surface and bottom currents flowed landward with the energy input from the strong winds and waves during the event. The storm triggered a notable landward salt flux and strong vertical mixing in the middle and lower PRE. The Stokes drift and wave forces played important roles in coastal storm surge and landward water transport, but the waves had a limited effect on enhancing mixing during the storm. Moreover, no evident changes were identified by the effect of surface wave roughness and WCI-enhanced bottom stress in the PRE. For the momentum balance, the local momentum balance was among the pressure gradient force, the Coriolis force and bottom stress before the storm, whereas both pressure gradient force and bottom stress were greatly enhanced with waves, resulting in a main balance among the surface stress, wave forces and pressure gradient force during the storm. After the typhoon, the PRE experienced a recovery with the recovery time varying from hours for water level to a week for river plume structure. This research highlights that the WCI effects are important in both storm surge and water transport.