Experimental Investigation of Wave Attenuation through Model and Live Vegetation

Abstract

Wetland vegetation can attenuate storm surge and waves and thus play an important role in coastal protection. In this study, laboratory experiments were used to quantify wave attenuation as a function of vegetation type, density, and height, as well as wave conditions. Wave attenuation characteristics were investigated under regular and irregular waves for rigid and flexible model vegetation in addition to live Spartina alterniflora and Juncus roemerianus, two common coastal species. Vegetation densities were 156–623 stems/m2 for model vegetation, 405–545 stems/m2 for S. alterniflora, and 2,857 stems/m2 for J. roemerianus. Bulk drag coefficients (CD) of the vegetation species were calibrated based on wave gauge data and video images, and regression equations were derived for the drag coefficient as a function of Keulegan-Carpenter number (KC). CD did not depend significantly on the relative vegetation height with respect to water depth for rigid vegetation models in the emergent and submerged conditions tested here. In general, drag coefficients were higher for live vegetation species than for rigid and flexible vegetation models. The results also showed that vertical variation of plant density strongly influenced the drag coefficient.