Coupling of Hydrodynamic and Wave Models: Case Study for Hurricane Floyd (1999) Hindcast

This paper demonstrates a practical application of coupling a hydrodynamic model with a wave model for the calculation of storm tide elevations in the St. Johns River (Northeastern Florida). Hurricane Floyd (1999) is chosen as the storm of interest due to its track which paralleled the northeast coast of Florida without making a direct landfall on the St. Johns River. The advanced circulation (ADCIRC) numerical code is applied as the hydrodynamic model for the computation of two-dimensional circulation resulting from astronomic tides and meteorologically induced storm surge. The simulating waves nearshore (SWAN) numerical code is applied as the wave model for the computation of wind-induced waves. Two model implementations are considered in order to investigate the effect of short wave contributions on the overall storm tide water level: (1) a one-way coupling procedure that transfers gradient of wave radiation stresses from SWAN to ADCIRC; and (2) a two-way coupling procedure that builds on the former to include feedback of water levels and currents from ADCIRC to SWAN. Simulated storm tide elevations are compared to historical National Ocean Service data to result in two major conclusions: (1) wind-induced waves play a significant role in the storm tide (contributing 10-15% of the peak water level), namely with respect to the transfer of momentum from the dissipation of short waves to the long-wave motion of the storm surge; and (2) a local-scale hydrodynamic model requires the application of a hydrograph boundary condition in order to account for the remote effects of the storm surge response.