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