Flume experiments on wind induced flow in static water bodies in the presence of protruding vegetation

Abstract

The problem of wind-induced flow in inland waters is drawing significant research attention given its relevance to a plethora of applications in wetlands including treatment designs, pollution reduction, and biogeochemical cycling. The present work addresses the role of wind induced turbulence and waves within an otherwise static water body in the presence of rigid and flexible emergent vegetation through flume experimentation and time series analysis. Because no prior example of Particle Imaging Velocimetry (PIV) experiments involving air-water and flexible oscillating components have been found in the literature, a spectral analysis framework is needed and proposed here to guide the analysis involving noise, wave and turbulence separation. The experiments reveal that wave and turbulence effects are simultaneously produced at the airwater interface and the nature of their coexistence is found to vary with different flow parameters including water level, mean wind speed, vegetation density and its flexibility. For deep water levels, signature of fine-scaled inertial turbulence is found at deeper layers of the water system. The wave action appears stronger close to the air-water interface and damped by the turbulence deeper inside the water system. As expected, wave action is found to be dominated in a certain frequency range driven by the wind forcing, while it is also diffused to lower frequencies by means of (wind-induced) oscillations in vegetation. Regarding the mean water velocity, existence of a counter-current flow and its switching to fully forward flow in the direction of the wind under certain combinations of flow parameters were studied. The relative importance of wave and turbulence to the overall energy, degree of anisotropy in the turbulent energy components, and turbulent momentum transport at different depths from the air-water interface and flow combinations were then quantified. The flume experiments reported here differ from previous laboratory studies in the related literature involving vegetation in the sense that the wave forcing is only present on the water surface contrary to a full-body excitation by tidal wave simulators and thus important in advancing the knowledge regarding a wider range of water resource problems.

Wind‐driven water motions in wetlands with emergent vegetation

“…This density is on the lower end of naturally occurring vegetation density, based on a literature survey of wetland plants similar to Tule and Typha [Poindexter, 2014]. Expressing the density as frontal area per area of wetland footprint, we calculate a nondimensional density of 0.15, which is about half that of the ''sparse'' case studied by [Banerjee et al, 2015].…”

“…Only Banerjee et al . [] has discussed this issue, describing (among other things) the interacting dynamics of waves, turbulence, and water depth.…”

“…How these processes change in the presence of vegetation has received little attention to date. Only Banerjee et al [2015] has discussed this issue, describing (among other things) the interacting dynamics of waves, turbulence, and water depth.…”

Effect of the Number of Leaves in Submerged Aquatic Plants on Stream Flow Dynamics

“…Dodds and Biggs [16] developed a model unifying attenuation by periphyton and macrophytes using the biomass density as the independent variable, which explained 80% of the variation in attenuation. In addition, the conditions of the river bed and the external environment also have some impact on the flow [17][18][19]. Devi and Kumar [18] investigated the characteristics of turbulent flow in a vegetative channel with seepage and found that seepage increased the maximum Reynold's stress and turbulence intensity.…”

Revisiting Kelvin Helmholtz Instabilities and von Kármán Vortices in Canopy Turbulence

“…So we use an energy filtering criterion based on a Lorentz curve analysis as presented in Banerjee et al (2015). The energy 5 filtering criterion follows the same philosophy employed in POD analysis, that most of the energy of a physical process is contained by the top few wave numbers (the velocity time series at every grid point are Fourier transformed to find the energy associated with every wavenumber.…”