CHARACTERIZING THE RELATIVE VELOCITY OF SEAGRASS BLADES UNDER OSCILLATORY FLOW CONDITIONS IN THE SANTA ROSA SOUND, FLORIDA

Various factors contributing to the ability of seagrass to attenuate waves and currents have been identified in the literature, but the roles of plant-induced reflection and movement remain poorly understood. To quantify how seagrass blade movement affects wave attenuation, an investigation was conducted in northwest Florida. The goals of this localized study were to quantify the wave attenuating properties of a seagrass bed under normal forcing conditions, measure the oscillatory flow velocity at the top and directly above a seagrass canopy while measuring the velocity of individual seagrass blades, and calculate the relative velocity of seagrass blades under oscillatory flow conditions and the applied force of these blades upon the water. A linear array of five RBR wave and tide recorders were deployed across a combined Thalassia testudinum and Halodule wrightii seagrass bed, with the resulting decay in wave height expressed as an exponential drag coefficient. Two Nortek velocimeters placed above the seagrass canopy measured flow velocities while a digital video recorder captured movement of individual seagrass blades. Frame by frame analysis of the video facilitated the quantification of seagrass movement under oscillatory flow. The relative velocity of the seagrass blades were calculated as the difference in water velocity and blade velocity. Along with the drag coefficient, relative velocity was then used to calculate plant induced horizontal force per unit volume.