Implementation and comparison of the recent three-dimensional radiation stress theory and vortex-force formalism in an unstructured-grid coastal circulation model

Given the importance of wave-current interaction in estuarine and coastal dynamics, it is crucial to revisit impacts of surface gravity waves on three-dimensional (3D) nearshore circulation. This work investigates wave-induced circulation in three typical coastal systems including an idealized inlet and planar and natural barred beaches, by implementing the recent 3D radiation stress (RS) theory and vortex-force (VF) formalism to an unstructured-grid Finite-Volume Community Ocean Model (FVCOM). In the idealized inlet case, 3D RS generated appreciable currents near barriers and lateral boundaries while VF forced strong flows via breaking and roller-induced accelerations in front of the inlet. Both simulations indicate vertically varying wave-induced circulation that decreases markedly. In the planar beach with obliquely incident waves, both methods successfully produced surface onshore and bottom undertow, as well as the wave breaking and roller-induced longshore currents. Nevertheless, 3D RS generated unrealistic offshore currents close to the shoreline. The coupled models were validated against observations in the natural barred beach, and results indicate that the 3D RS model agrees slightly better with the observed longshore currents while 3D VF captures the vertical shear of the onshore-offshore flows reasonably. Further investigations suggest that both methods produce the wave breaking-induced surface onshore and bottom undertow successfully, yet they are located further offshore resulting from the 3D RS-induced unrealistic offshore currents. Successful implementations of the paired wave-current theories to the unstructured model would be fundamental and beneficial to the coastal ocean modeling community.