Effects of Posidonia oceanica seagrass meadows on storm waves

Recent research indicated that submerged vegetation located at the sea bottom cause wave attenuation. The ratio of wave attenuation highly depends on the type of vegetation as the morphological and physical features of vegetation determine the water column occupied by the vegetation that would in turn lead to wave attenuation. Therefore, it is hard to agree on a single wave attenuation ratio that covers every species. The aim of this study is to find out wave attenuation and wave energy dissipation ratios specifically for Posidonia oceanica. Posidonia oceanica, known to occupy a high water column, is an endemic seagrass species that exists in the Mediterranean Sea. For attaining this purpose, experiments were conducted in a pilot wave flume located at the Hydraulics Laboratory of Istanbul Technical University. 1:10 scaled Posidonia oceanica models were manufactured and artificial seagrass meadow were established on a sandy sloping bottom. Wave heights identified in the vegetated and unvegetated areas were then compared. It is determined that vegetation attenuates wave height and dissipates wave energy. Ratio of wave height under the vegetated and unvegetated conditions varied between 0.78 and 0.94, and it is observed that wave energy dissipation by vegetation varies between 11- 40%. In addition, vegetation affects wave height even more as it approaches to the shoreline.