Typhoon Morakot Induced Waves and Surges with an Integrally Coupled Tide-Surge-Wave Finite Element Model

Abstract

A coupled system of unstructured-mesh SWAN and ADCIRC, running on the same unstructured mesh, has beenapplied to simulate storm surges and waves during typhoon Morakot in August 2009. Emphasis is placed on theeffect of wave-tidal current interaction on storm surges and wind waves. Two advantages of this system are that thephysics of wave-circulation interactions can be satisfactorily resolved, and a large domain covering a deep ocean andshallow shelf can be dealt with seamlessly, requiring no mesh nesting. Wave refraction and directional spreadinginduced a wave-current effect, which was confirmed by the cross correlation between the observed significant waveperiods and the wave-current angle. The results from the application of the system show that waves resulting from atyphoon can be reasonably simulated in a coastal area. The effect of coupling wave heights and wave periods isfound to be approximately 5% and 10%, respectively. Spectral characteristics such as directional spreading andrefraction support the influence of tidal current effects on wind waves. This coupled system is a good starting pointfor operational wave-tide-surge forecasting and can be easily extended to regional sites of interest without asignificant increase in the computational burden. The system currently uses a set of depth-integrated equations thatsimplifies the vertical structure of the current, radiation stress, surface stress and bottom boundary layer.