Surface wave attenuation by vegetation with the stem, root and canopy

Abstract

To experimentally study the performance of the stem, root and canopy on wave attenuation by vegetation, a total of 112 laboratory experiments were conducted with seven vegetation models, four vegetation densities, five wave heights and four water depths. Wave period was assumed constant, limiting the understanding of wave attenuation phenomena by vegetation. Frictional energy losses from sidewall and bottom were measured and removed by comparing with non-vegetated tests. Experimental results show that wave attenuation by vegetation with stems, roots and canopies varied with wave conditions due to vertically non-uniform physical vegetation properties. The root significantly impacted wave dissipation when the relative root height was greater than 0.167. Higher wave attenuation occurred when the still water level was located at the canopy geometrical centroid. The transmission coefficients of vegetation of the stem, root and canopy ranged from 0.21 to 0.83. An empirical formula for predicting transmission coefficients of vegetation with stems, roots and canopies was obtained based on experimental data. The wave energy dissipated by vegetation was estimated in terms of drag coefficients calculated by analytical models of Dalrymple et al. (1984) and Kobayashi et al. (1993). A semi-empirical analytical equation was proposed on the basis of experimental data for predicting wave attenuation by vegetation of the stem, root and canopy.