Abstract
Vegetation plays a pivotal role in fluvial and coastal flows, affecting their structure and turbulence, thus having a strong impact on the processes of transport and diffusion of nutrients and sediments, as well as on ecosystems and habitats. In the present experimental study, the attenuation of regular waves propagating in a channel through flexible vegetation is investigated. Specifically, artificial plants mimicking Spartina maritima are considered. Different plant densities and arrangements are tested, as well as different submergence ratios. Measurements of wave characteristics by six wave gauges, distributed all along the vegetated stretch, allow us to estimate the wave energy dissipation. The flow resistance opposed by vegetation is inferred by considering that drag and dissipation coefficients are strictly related. The submergence ratio and the stem density, rather than the wave characteristics, affect the drag coefficient the most. A comparison with the results obtained in the case when the same vegetation is placed in a uniform flow is also shown. It confirms that the drag coefficient for the canopy is lower than for an isolated cylinder, even if the reduction is not affected by the stem density, underlining that flow unsteadiness might be crucial in the process of dissipation.
Highlights
Coastal wetlands and saltmarshes are fundamental for sustaining ecosystems and preserving coasts from erosion and flooding due to storm surge and waves [1,2,3]
Circles denote the experimental data, dashed line are the modeled wave attenuation either with (a) the exponential model given by Equation (6); or (b) the hyperbolic model given by Equation (4)
The present work investigated the resistance to flow of flexible vegetation in waves and in uniform flow conditions
Summary
Coastal wetlands and saltmarshes are fundamental for sustaining ecosystems and preserving coasts from erosion and flooding due to storm surge and waves [1,2,3]. Vegetation attenuates the action of waves, slows down the flow, and promotes diffusion and deposition processes [6,7,8,9,10]. It (i) enhances particle removal and water quality [11,12,13]; (ii) positively affects the hydrochory and nautochory of seeds and organic matter [14,15,16,17]; (iii) reduces sediment erosion and resuspension, while enhancing sediment deposition [18,19,20]; and (iv) creates preferred paths for tracers’.
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