Experimental wave attenuation study over flexible plants on a submerged slope

Abstract

Using plants is a kind of environmentally-friendly coastal protection to attenuate wave energy. In this paper, a set of experiments were conducted to investigate the wave attenuation performance using flexible grasses on a submerged slope, and the wave attenuation coefficient for these experiments was calculated for different still water depths, slope and grass configurations. It was found that the slope plays a significant role in wave attenuation. The wave attenuation coefficient increases with increasing relative row number and relative density. For a small relative row number, the two configurations from the slope top to its toe and from the slope toe to its top performed equally to a large extent. For a medium relative row number, the configuration from the slope toe to its top performed more poorly than that from the slope top to its toe; however, it performed better than that from the slope top to its toe for a high relative row number. With a single row of grasses close to the slope top from the slope toe, the wave attenuation coefficient shows double peaks. With increasing grass rows or still water depth, the grass location corresponding to the maximum wave attenuation coefficient is close to the slope top. The dimensional analysis and the least square method were used to derive an empirical equation of the wave attenuation coefficient considering the effect of relative density, the slope, the relative row number and the relative location of the middle row, and the equation was validated to experimental data.