Effect of fallen posidonia oceanica seagrass leaves on wave energy at sandy beaches

Posidonia Oceanica (PO) is an endemic marine vegetation for the Mediterranean Sea. In an experimental study, conducted in the Eastern Mediterranean, natural dead PO leaves are measured to reduce incident wave heights impacting the beach. Transmission coefficient (K_t) was found to vary between 0.73-0.94 which is equivalent to a wave height decay of 6-27%. The results show that the free-floating dead PO leaves in their natural environment dissipate incoming wave energy and have a capacity to protect the beach against erosion. Further analysis in separate frequency bands show that short waves (with periods less than 4.4 s) are more sensitive to PO leaves in terms of energy dissipation. The transmission coefficient for short waves as calculated using the high frequency part of the wave spectrum, delivered a maximum transmission coefficient of 0.5 corresponding to 50% wave height decay due to PO leaves.2D model was established with an open-source software and calibration of the model was done with data without PO leaves. Vegetation parameters are incorporated to the calibrated model and wave decays are calculated by changing drag coefficients and second calibration of the model is done with vegetation with mean-root-square error of 4 mm which is 2 % of the observed wave heights. Free parameter selected for calibration was drag coefficient (CD) and kept fixed throughout the analysis since the Reynold's number was in the range of 4-9.103 . Finally, an empirical, wave length depended wave decay formula is derived.