Abstract
Abstract. Vegetation in wetlands is a large-scale nature-based resource providing a myriad of services for human beings and the environment, such as dissipating incoming wave energy and protecting coastal areas. For understanding wave height attenuation by vegetation, there are two main traditional calibration approaches to the drag effect acting on the vegetation. One of them is based on the rule that wave height decays through the vegetated area by a reciprocal function and another by an exponential function. In both functions, the local wave height reduces with distance from the beginning of the vegetation depending on damping factors. These two damping factors, which are usually obtained from calibration by measured local wave height, are linked to the drag coefficient and measurable parameters, respectively. So the drag coefficient that quantifies the effect of the vegetation can be calculated by different methods, followed by connecting this coefficient to hydraulic parameters to make it predictable. In this study, two relations between these two damping factors and methods to calculate the drag coefficient have been investigated by 99 laboratory experiments. Finally, relations between the drag coefficient and relevant hydraulic parameters were analyzed. The results show that emergent conditions of the vegetation should be considered when studying the drag coefficient; traditional methods which had overlooked this condition cannot perform well when the vegetation was emerged. The new method based on the relation between these two damping factors performed as well as the well-recognized method for emerged and submerged vegetation. Additionally, the Keulegan–Carpenter number can be a suitable hydraulic parameter to predict the drag coefficient and only the experimental setup, especially the densities of the vegetation, can affect the prediction equations.
Highlights
To meet the current wave prevention requirements, it is practical to construct ecological safety barriers with wetland vegetation based on natural conditions
Wave height along the vegetated area is a significant index for wave attenuation by vegetation
Wave attenuation by vegetation in wetlands is a large-scale nature-based solution providing a myriad of services for human beings
Summary
To meet the current wave prevention requirements, it is practical to construct ecological safety barriers with wetland vegetation based on natural conditions. It is necessary to better understand the mechanism of wave attenuation to promote the efficiency of the nature-based solution. The drag force is closely related to the drag coefficient CD which quantifies the drag or resistance of vegetation in water (Chen et al, 2018). This coefficient is one of the most uncertain parameters in the complicated interaction
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