Turbulence and Bed Load Transport in Channels With Randomly Distributed Emergent Patches of Model Vegetation

Abstract

Laboratory experiments explored the impact of vegetation patchiness on channel-averaged turbulence and sediment transport. Stems were clustered into 16 randomly distributed circular patches of decreasing diameter. For the same channel velocity, the sediment transport increased with total stem number but decreased as stems were clustered into smaller patch diameters, occupying a smaller fraction of the bed area. The channel-averaged turbulence, which also declined with increased clustering, was shown to be a good predictor for sediment transport at the channel scale. Previous models for uniform vegetation were adapted to predict both the channel-averaged turbulence and sediment transport as a function of the total number of stems and degree of clustering, represented by the fraction of bed covered by patches. This provides a way for numerical modelers to represent the impact of subgrid-scale vegetation patchiness on sediment transport.

Quantifying Seasonal Seagrass Effects on Flow and Sediment Dynamics in a Back‐Barrier Bay

“…However, this uniform vegetation approach may not be able to reproduce some heterogeneous patterns observed within seagrass meadows associated with spatial gradients in seagrass density, such as spatially variable accretion rates (Ganthy et al., 2013). Moreover, our model grid size (∼70 m) was too coarse to resolve seagrass patchiness (usually on a scale of several meters), which has been shown to impact the distributions of bed shear stress and sediment transport rates, and consequent light environments for seagrass growth (Carr et al., 2016; Shan et al., 2020).…”

Turbulence Dictates Bedload Transport in Vegetated Channels Without Dependence on Stem Diameter and Arrangement

“…In a random array, two lateral transects provided an accurate estimate of E U and 〈 t E k〉. Specifically, the velocity statistics converged to a constant value after averaging two complete transects chosen randomly along the array (see supporting information in Shan et al, 2020). Along each transect, two locations whose time-mean streamwise velocity and TKE were closest to the transect mean were selected for a vertical profile.…”

Influence of submerged flexible vegetation on turbulence in an open-channel flow

“…Natural rivers and lakes are complex three-dimensional (3-D) ecosystems with different types of vegetation at different levels. The existence of vegetation can not only slow down the flow velocity and stabilise the riverbed, but also play an important ecological role purifying the water, beautifying the environment and providing the habitat for invertebrates, fish and other aquatic organisms (Nepf 2012;Shan et al 2020). Therefore, it is of great significance to study the flow-vegetation interaction for analysing the turbulence structure and material transport from the perspective of protecting the aquatic ecological environment.…”

“…The direct simulation method is more convenient to study the physical mechanism of the flow-vegetation interaction (Stoesser et al 2009;Maza, Lara & Losada 2015;Boothroyd et al 2016;Wolski & Tymiński 2020), and mass and momentum transport (Mayaud, Wiggs & Bailey 2016;Kim, Kimura & Park 2018;Liu et al 2018). Presently, most of these models are 3-D rigid vegetation models, in which rigid cylinders were used to simulate the effects of plants on the flow (Stoesser, Kim & Diplas 2010;Huai, Xue & Qian 2015;Etminan, Lowe & Ghisalberti 2017). Neary et al (2012) established a numerical model of rigid emergent plants based on the large-eddy simulation (LES) method to study the influence of the stems of emergent plants on the turbulence characteristics and sediment transport.…”