Wave attenuation in stands of common reed(Phragmites australis) and its consequences on sediment resuspension

Abstract: Common reed is found in near-shore areas of many European lakes, where it forms dense stands. As waves are influenced by obstacles along the wave path, water and sediment motions caused by waves are affected by these stands. This study aims to evaluate the effect of common reed stands on waves, evaluate the effect of common reed stands on wave induced sediment resuspension, test a model for wave attenuation by vegetation and discuss extensive common reed stands consequences to sediment induced turbidity in lakes. In order to evaluate the effects of common reed stands on waves, a field experiment was conducted in the common reed stands of a southern Swedish lake. The water surface displacement was measured simultaneously both within and outside these stands. According to the wave measurements, the significant wave height decreases within stands of common reed, while the average period seems to increase. Based on the applied analysis of the wave measurements, it was impossible tell whether or not stands of common reed reduce the resuspension potential of wave regimes. This was not due to the wave measurements, but to a flaw in the analysis of the wave measurements. Visual observations indicated however that stands of common reed reduce wave breaking and thereby sediment resuspension. The model was adjusted to the prevailing wave regime with the drag coefficient and the drag coefficient seems to be dependent on Reynolds number.