Influence of particle size and density, and channel velocity on the deposition patterns around a circular patch of model emergent vegetation

Abstract

This laboratory study examined the influence of particle size and density, and channel velocity on the spatial deposition pattern around an emergent (extending through the entire water depth), circular patch of model vegetation located at the center of a channel. Three flow conditions and three particles of different size and density were considered. Across all particle and velocity conditions, three basic deposition patterns were observed: (1) high deposition in the patch wake and low deposition in the zones adjacent to the patch; (2) high deposition in both the wake and adjacent zones; and (3) low deposition in both the wake and adjacent zones. The observed deposition pattern correlated with the ratio of channel shear velocity (u Ã Þ to critical shear velocity (u Ãc Þ: Specifically, for u à =u Ãc < 0:7 or u à =u Ãc > 3, the deposition was high (or low, respectively) over the entire channel with little difference between the wake and adjacent regions. In contrast, for 0:7 < u à =u Ãc < 3 divergence in net deposition between the wake and the adjacent zones occurred, with higher net deposition in the wake and lower net deposition in the adjacent zones. The peak divergence was observed at u à =u Ãc 51:6. The deposition patterns were more closely correlated with the ratio u à =u Ãc than with w s =u à (with w s the particle settling velocity), suggesting that the spatial variation in net deposition was driven by resuspension (associated with u Ãc ) and not settling (associated with w s ).

Investigating the turbulent flow characteristics in an open channel with staggered vegetation patches

“…Different positions at 1 D upstream and downstream of the circular vegetation patch were selected to investigate the flow properties (as shown in Figure a,c). This type of experimental setup has also been used by many researchers upstream and downstream of individual vegetation elements (Anjum, Ghani, Pasha, Latif, et al, ; Liu, Diplas, Hodges, & Fairbanks, ) as well as at some distance directly before and after circular patches of vegetation (Meire et al, ; Shi, Jiang, & Nepf, ). A flow rate of 0.009 m 3 /s was adopted in all the experiments.…”

Wake structure and sediment deposition behind models of submerged vegetation with and without flexible leaves

“…The adjustment of flow around finite patches of vegetation influences the spatial distribution of sediment deposition and erosion (Rominger et al 2010;Gurnell et al, 2012, Jones et al 2012. For example, net deposition is enhanced in the wake downstream of a finite patch; erosion is observed at the lateral edge of a patch; and within the patch, both deposition and erosion are observed (Bouma et al, 2007;Tanaka and Yagisawa, 2010;Schulz et al 2003;Follett et al 2012;Shi et al 2016, Liu andNepf 2016). By producing a nutrient-rich substrate, regions of enhanced fine-particle deposition around patches of vegetation can drive patterns of future growth (Kondziolka and Nepf, 2014;Gurnell, 2014;Lima et al 2015).…”

Flexural Rigidity and Shoot Reconfiguration Determine Wake Length Behind Saltmarsh Vegetation Patches

“…Therefore, under many velocity conditions, wake sedimentation may not be distinguishable from deposition on the bare unvegetated bed. This phenomenon was studied by Shi et al (2016), who found both sediment and flow controls on preferential wake deposition. Determining a threshold condition for preferential wake deposition is key to comparing predicted wake deposition extents with field data.…”

“…Vegetation represents a porous blockage, which extracts energy from the flow as it crosses the patch, causing a wake to form behind, characterized by low bleed velocities and reduced turbulent kinetic energy (Nepf, ; Nicolle & Eames, ). Here, enhanced deposition may occur (e.g., Figure ), depending upon local sediment and flow conditions (Chen et al, ; Shi et al, ; Zong & Nepf, ). Where the flow reattaches, turbulent kinetic energy is higher, and vortex shedding may occur, which limits sediment deposition (Chen et al, ; Zong & Nepf, ).…”