Field study on flow structures within aquatic vegetation under combined currents and small‐scale waves

Zhang, Yinghao; Lai, Xijun; Ma, Jingxu; Zhang, Qian; Yu, Ru; Yao, Xin; Deng, Huanguang

doi:10.1002/hyp.14121

Cited by 10 publications

(9 citation statements)

References 62 publications

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“…Flume studies are by definition unable to capture all the spatial scales that may be relevant for hydrodynamic processes in natural systems (Bouma et al, 2007). Field and large‐scale studies involving patches of real‐scale riparian vegetation remain scarce (Berends et al, 2020; Ji et al, 2016; Västilä et al, 2019; Zhang et al, 2021). Simulating vegetation with simplified rigid surrogates in physical and numerical models disregards the seasonality and flexibility‐induced flow modifications that may be relevant for understanding and modelling hydromorphological and ecological processes in natural systems (Caroppi et al, 2021).…”

Section: Introductionmentioning

confidence: 99%

Flow and wake characteristics associated with riparian vegetation patches: Results from field‐scale experiments

Caroppi

Västilä

Järvelä

et al. 2022

Hydrological Processes

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Riparian vegetation patches growing on river banks and floodplains influence in‐channel and overbank hydromorphological processes. The current knowledge on patch‐scale hydrodynamics is largely based on laboratory flume experiments with simplified vegetation. The aim of this study is to provide new understanding of the flow and wake characteristics for real riparian vegetation patches based on field‐scale experiments with natural willows, in order to inform hydromorphological and ecological modelling. The focus was placed on the effects of foliage as the main driver of the seasonal changes in vegetation and on the influence of the flexibility‐induced reconfiguration on the flow in the wake and around the patches. The patch drag, defined by its flow blockage factor, was increased by 3.0–4.4 times by the presence of foliage and decreased by up to 60% because of the streamlining and reconfiguration of foliage with increasing flow velocity. Such large changes in the patch drag altered the flow and wake characteristics, affecting the onset of a patch‐scale vortex street. Seasonality and flexibility modified the patch sheltering effect, that is, the magnitude of velocity, turbulent kinetic energy, and bed shear stress reduction in the wake, relative to the background level. In the presence of foliage, mean flow velocity and bed shear stress in the wake were reduced on average by ~50% and ~70%, respectively. The sheltering effect was lower for the leafless conditions than for the foliated conditions. For the foliated cases, the spatial extents of the over‐depth and the near‐bed sheltered region were on average 1.5 and 1.8 times larger than in the corresponding leafless cases, respectively. Overall, seasonal changes in vegetation and flexibility‐induced mechanisms were identified as key controls for the flow associated with patches of riparian vegetation, with major implications on developing models for predicting hydromorphological processes and the potential to preserve and create habitats.

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Section: Introductionmentioning

confidence: 99%

Flow and wake characteristics associated with riparian vegetation patches: Results from field‐scale experiments

Caroppi

Västilä

Järvelä

et al. 2022

Hydrological Processes

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“…For example, researchers studied the impact of suspended sediment and sedimentation on turbulence and flow in mixing boxes (Huang et al., 2022), and analyzed the impacts of tidal flats geomorphology on tidal asymmetry and velocity skew in the Skagit Bay (Nidzieko & Ralston, 2012). Some other concerns, such as effects of vegetation (Schaefer and Nepf, 2022a, 2022b; Y. Zhang et al., 2021), artificial structures (Wu, 2010; W. Zhao, 2009; Zhou, 2019).…”

Section: Discussionmentioning

confidence: 99%

Positive Feedback Between the Tidal Flat Variations and Sediment Dynamics: An Example Study in the Macro‐Tidal Turbid Hangzhou Bay

Ren

et al. 2023

JGR Oceans

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Tidal flat variations (curvature) in macro‐tidal turbid bays highly correlate with sediment dynamics. Interactions between tidal flats and sediment dynamics in macro‐tidal turbid estuaries, like Hangzhou Bay, China, have been studied through a fully validated 3D sediment model by considering high‐turbidity, flocculation, and water‐sediment density coupling. Numerical results show that the circulation and sediment flux in the curvature of Andong tidal flat have similar magnitudes in the along‐estuarine and lateral directions, demonstrating the important impact of the geometry on hydrodynamics and sediment transport processes. Sediment moves toward the southern/northern bank near the bottom/surface level in curvature. Tidally averaged net sediment flux is southward in the curvature. Tidal flat reclamation changes the curvature of the tidal channel, and modulates the circulation and sediment transport, and then feeds back to the tidal flat evolution subsequently. Bottom friction, nonlinear advection, and centrifugal force are dominant forces for inducing the lateral circulation, followed by the Coriolis force and sediment‐induced baroclinic process. Lateral circulation combined with the suspended sediment concentration (SSC) profile controls the distribution of instantaneous and tidally averaged net sediment fluxes in the curvature. The sediment flux positively correlates with the curvature of channel bends. The increased curvature of channel bends enhances the southward sediment fluxes mainly by increasing the effects of the centrifugal force, nonlinear advection, and Coriolis force on the lateral circulation and SSC. This study revealed a two‐way feedback system between tidal flat and sediment dynamics, which contributes to the impact of anthropogenic activities on geomorphological evolution of similar estuaries worldwide.

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“…Paul and Gillis (2015) subjected a transplanted meadow of Zostera noltei to both pure current and combined wave-current conditions and observed no differences in timeaveraged velocity, but observed a reduction in TKE in combined wave-current conditions relative to corresponding pure current conditions, which is opposite to the trend observed for rigid models (e.g., Lou et al, 2018;Chen et al, 2020). In a field study on a floodplain of the Yangtze River and for multiple species of flexible vegetation, Zhang et al (2021) observed little impact of waves on the magnitude of TKE associated with the current, but observed that the presence of waves increased the shear layer penetration depth, δ e , relative to that predicted for pure current (Nepf et al, 2007), and they attributed this to the waving of the flexible leaves.…”

Section: Introductionmentioning

confidence: 90%

Flow Structure in an Artificial Seagrass Meadow in Combined Wave-Current Conditions

Schaefer

Nepf

2022

Front. Mar. Sci.

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Experiments were conducted in a laboratory flume using an artificial seagrass meadow, modeled after Zostera marina, to examine the impact of waves on the vertical structure of time-averaged current, Reynolds stress, and turbulent kinetic energy (TKE) under combined wave-current conditions. With the addition of smaller waves, defined by a ratio of wave velocity to current velocity Uw/Uc < 2.5, the time-averaged velocity peaked above the meadow, which was similar to pure current conditions. When Uw/Uc > 2.5, the presence of waves caused the time-averaged velocity to peak near the top of the meadow. For Uw/Uc > 1 the presence of waves reduced the magnitude of peak Reynolds stress. For all conditions considered, the wake production of turbulence dominated the shear production of turbulence in the meadow. However, the wave velocity was less efficient than the current velocity in generating TKE in the meadow because the movement of the blades forced by the oscillatory fluid motion reduced the relative velocity between the blades and the wave. A modified hybrid model for wake production of TKE in a flexible canopy under combined wave-current conditions was proposed to account for the relative contributions of waves and currents. Wake production of TKE was dominated by waves when Uw/Uc > 1 and dominated by currents when Uw/Uc < 1. The models and observations proposed in this study contribute to an enhanced understanding of the relative influences of waves and currents on seagrass meadow flow structure in realistic combined wave-current conditions.

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Field study on flow structures within aquatic vegetation under combined currents and small‐scale waves

Cited by 10 publications

References 62 publications

Flow and wake characteristics associated with riparian vegetation patches: Results from field‐scale experiments

Flow and wake characteristics associated with riparian vegetation patches: Results from field‐scale experiments

Positive Feedback Between the Tidal Flat Variations and Sediment Dynamics: An Example Study in the Macro‐Tidal Turbid Hangzhou Bay

Flow Structure in an Artificial Seagrass Meadow in Combined Wave-Current Conditions

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