The biomechanics of salt marsh vegetation applied to wave and surge attenuation

Abstract

The Northern coast of the Gulf of Mexico is threatened by storm surge and waves from tropical storms. It has been long known that marsh vegetation attenuates storm surge and waves and is vital for sustaining marsh edges. However, little is known about the relationship between plant properties and the amount of storm surge and wave reduction the plants provide. In order to better understand the stiffness properties and physical dimensions of saltmarsh vegetation, which are directly related to their ability to attenuate waves and storm surge, this study has been conducted. Stiffness of salt marsh vegetation was determined through direct bending and through board drop testing at several locations along the Southeast Louisiana Gulf Coast from August 13, 2009 to September 15, 2011. Biomechanical properties of salt marshes, including plant dimension and bending stiffness modulus, were measured on coastal marshlands on the Southeast gulf coast of Louisiana, and are correlated with plant total height, stem height, stem diameter, plant stem density, and seasonal variations and botanical behavior. Two methods were employed, including direct stem bending and indirect board drop tests. The dataset is analyzed in depth to develop empirical equations of plant stiffness and compared with those found in the literature based on vegetation on river floodplains. These wave and surge measurements along with vegetation data are applicable to calibrating wave models that incorporate the reduction of energy due to wetland vegetation. The mitigation of wave energy and storm surge is critical to the survival of Louisiana’s wetlands and coastline. Salt marsh vegetation has the ability to mitigate the potential damage caused by storm surges and large waves. This study will improve our understanding of the role of vegetation in attenuating waves and storm surge and the accuracy of the parameterization of the vegetation effects in the-state-of-the-art wave models. The successful quantification of wave and surge attenuation by salt marshes will be a positive contribution to Louisiana’s hurricane protection and coastal restoration efforts.