Mean and turbulent velocity fields near rigid and flexible plants and the implications for deposition

Abstract

[1] The transport of fine sediment and organic matter plays an important role in the nutrient dynamics of shallow aquatic systems, and the fate of these particles is closely linked to vegetation. We describe the mean and turbulent flow near circular patches of synthetic vegetation and examine how the spatial distribution of flow is connected to the spatial distribution of suspended sediment deposition. Patches of rigid, emergent, and flexible, submerged vegetation were considered, with two different stem densities. For the rigid emergent vegetation, flow adjustment was primarily two-dimensional, with flow deflected in the horizontal plane. Horizontal shear layers produced a von Kármán vortex street. Flow through the patch shifted the vortex street downstream, resulting in a region directly downstream of the patch in which both the mean and turbulent velocities were diminished. Net deposition was enhanced within this region. In contrast, for the flexible, submerged vegetation, flow adjustment was three-dimensional, with shear layers formed in the vertical and horizontal planes. Because of strong vertical circulation, turbulent kinetic energy was elevated directly downstream of the patch. Consistent with this, deposition was not enhanced at any point in the wake. This comparison suggests that morphological feedbacks differ between submerged and emergent vegetation.

Multiple Stable States and Catastrophic Shifts in Coastal Wetlands: Progress, Challenges, and Opportunities in Validating Theory Using Remote Sensing and Other Methods

“…The role of vegetation has been investigated in laboratory experiments and is now receiving greater attention in field studies. Laboratory investigations of irregular obstacles, such as dispersed vegetation patches, have shown how they cause complicated disturbances that can spread into the patches, with irregular effects on inter-and intra-patch sedimentation [184][185][186]. The observation of such results in experiments with both channelized and sheet water flows is particularly relevant to the spatially variable flow conditions of freshwater marshes and deltas.…”

Resistance and reconfiguration of natural flexible submerged vegetation in hydrodynamic river modelling

“…These mutual plant-flow interactions have important effects on the hydraulic, ecological and geomorphic functioning of lowland rivers [7][8][9] and it is therefore crucial to implement plant-flow interactions in hydrodynamic models. Plant-flow interactions have been relatively well studied in recent years through numerical modelling [10,11], laboratory experiments [12][13][14][15] and field measurements [8,16]. Vegetation resistance can be quantified via empirical relationships or with Environ Fluid Mech hydrodynamic models.…”

“…Experiments with flexible vegetation patches have been executed by e.g. [12,[42][43][44]. Secondly, the morphology of the vegetation is traditionally represented by the stem diameter and number of stems per unit horizontal area.…”

Experimental Investigations of Scour Pools around Porous Obstructions

“…However, for h/h p = 1.6, flow is vertically deflected as well. If more flow is deflected over the obstructions, the acceleration of flow decreases at a contraction region [19]. This indicates that as the submergence ratio increases, the flow deflection in the horizontal plane decreases, and this implication is more pronounced because more flow is able to pass over the obstructions.…”