Effect of a seagrass (Posidonia oceanica) meadow on wave propagation

We demonstrate the utility of using the equivalent bottom roughness for calculating the friction factor and the drag coefficient of a seagrass meadow for conditions in which the meadow height is small compared to the water depth. Wave attenuation induced by the seagrass Posidonia oceanica is evaluated using field data from bottom-mounted acoustic doppler velocimeters (ADVs). Using the data from one storm event, the equivalent bottom roughness is calculated for the meadow as k(s) similar to 0.40 m. This equivalent roughness is used to predict the wave friction factor f(w), the drag coefficient on the plant, CD, and ultimately the wave attenuation for other storms. Root mean squared wave height (H-rms) is reduced by around 50% for incident waves of 1.1 m propagating over similar to 1000 m of a meadow of P. oceanica with shoot density of similar to 600 shoots m(-2).