The effect of an emergent vegetation (i.e. Phragmistes Australis) on wave attenuation and wave kinematics

Abstract

Coastal vegetation acts as a natural barrier at many coastal zones, protecting the landside against wave effects and coastal erosion. It is known that coastal vegetation affects wave properties, and studies regarding this topic have been made in a wide variety, mostly focusing on wave attenuation. In this study, laboratory experiments have been conducted in a wave basin to inspect the effect of an emergent vegetation on wave attenuation, wave transformation and wave kinematics. A blank area is present along the reed field, which enables energy transformation during wave propagation. Three different regular waves have been sent to a natural reed field, and wave heights and kinematics have been measured around the structure. The results indicate that crest-parallel energy transmission takes place as the waves propagate along the reed field, which is boosted at the end of the reed, and the transmission becomes faster on waves with higher wave steepness. Measured water particle velocities have been evaluated to obtain the steady-cyclic and fluctuation components, by which, turbulence intensities in front and at the wake of the reed field have been evaluated. The results indicate that turbulence intensity increases at the mid-depth at the wake of the structure, becoming higher with increasing wave steepness. Thus, one may conclude that energy dissipation takes further place after the end of the reed field due to turbulence.