Development and validation of a three-dimensional, wave-current coupled model on unstructured meshes

Abstract

Using unstructured meshes provides great flexibility for modeling the flow in complex geomorphology of tidal creeks, barriers and islands, with refined grid resolution in regions of interest and not elsewhere. In this paper, an unstructured three-dimensional fully coupled wave-current model is developed. Firstly, a parallel, unstructured wave module is developed. Variations in wave properties are governed by a wave energy equation that includes wave-current interactions and dissipation representative of wave breaking. Then, the existing Finite-Volume Coastal Ocean Model (FVCOM) is modified to couple with the wave module. The couple procedure includes depth dependent wave radiation stress terms, Stokes drift, vertical transfer of wave-generated pressure transfer to the mean momentum equation, wave dissipation as a source term in the turbulence kinetic energy equation, and mean current advection and refraction of wave energy. Several applications are presented to evaluate the developed model. In particular the wind and wave-induced storm surge generated by Hurricane Katrina is investigated. The obtained results have been compared to the in situ measurements with respect to the wave heights and water level elevations revealing good accuracy of the model in reproduction of the investigated events. In a comparison to water level measurements at Dauphin Island, inclusion of the wave induced water level setup reduced the normalized root mean square error from 0.301 to 0.257 m and increased the correlation coefficient from 0.860 to 0.929. Several runs were carried out to analyze the effects of waves. The experiments show that among the processes that represent wave effects, radiation stress and wave-induced surface stress are more important than wave-induced bottom stress in affecting the water level. The Hurricane Katrina simulations showed the importance of the inclusion of the wave effects for the hindcast of the water levels during the storm surge.