Location: Watershed Physical Processes ResearchTitle: Analysis of vegetation effect on waves using a vertical 2-D RANS model) Author
Submitted to: Journal of Coastal Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/19/2012
Publication Date: 3/1/2013
Citation: Wu, W., Zhang, M., Ozeren, Y., Wren, D.G. 2013. Analysis of vegetation effect on waves using a vertical 2-D RANS model. Journal of Coastal Research. 29(2):383-397. Interpretive Summary: Hurricanes and tropical storms often cause severe damage and loss of life in coastal areas. It is widely recognized that wetlands along coastal fringes reduce storm surge and waves. Yet, the potential role and primary mechanisms of wave mitigation by wetland vegetation are not fully understood. Knowledge of the reduction in wave height and energy as the waves encounter obstacles such as marsh grasses is essential for assessing the ability of vegetation to limit wave damage. It is also important for coastal marsh restoration design, where the width of the restored or established marsh may be based how the waves will be reduced as they cross the marsh. The goal of this paper is to demonstrate the use of a computer model to describe the attenuation of waves as they pass through marsh grasses. The computer model was developed and validated with consideration of recent experimental results on wave/grass interaction obtained in the wave flume at the National Sedimentation Laboratory. The computer model will allow the experimental results to be extended into a predictive capacity that will be useful for future projects in marsh restoration and creation as will as in predicting the inland penetration of waves impacted coastal marsh areas.
Technical Abstract: A vertical two-dimensional (2-D) model has been applied in the simulation of wave propagation through vegetated water bodies. The model is based on an existing model SOLA-VOF which solves the Reynolds-Averaged Navier-Stokes (RANS) equations with the finite difference method on a staggered rectangular grid and uses the volume of fluid method to capture the free surface. The model is enhanced in this study by adding the drag and inertia forces in the momentum equations to account for the vegetation effects, implementing the sub-grid scale model for turbulence closure, and incorporating wave maker, sponge layer and bottom friction in boundary conditions. The model was first validated using measurement data collected from the literature, and then applied to simulate wave propagation in flumes covered by rigid and flexible model and live vegetation. The considered live vegetation species are Spartina alterniflora (smooth cord grass) and Juncus roemerianus (needlegrass rush), which are commonly distributed on coastlines. The model is able to reproduce wave attenuation through the vegetation zone observed in the experiments. The drag coefficients are calibrated in the vertical 2-D RANS model and also the analytical model based on the wave energy equation and linear wave theory, and the calibrated values in the two models are reasonably close.