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A bank‐stability analysis is incorporated into an analytical procedure for modeling the hydraulic geometry of an alluvial gravel‐bed channel. The new analysis includes a procedure that calculates the mean bed and bank shear stress as well as assessing the bank stability. The bank‐stability criterion accounts for the increased stability of the channel banks due to consolidation of the bank sediment, cementing by fines, and binding of the sediment by root masses. The two key parameters in the bank‐stability analysis are the median grain diameter of the bank sediment D50bank, and the modified friction angle of the bank sediment φ′. A sensitivity analysis of the two parameters indicate that the bank stability can exert a large influence on the channel geometry. This is supported by testing the theory on published field data. The bank sediment size was assumed to equal the bed sediment size, and the variation of the friction angle φ′ was investigated. The estimated φ′ values are seen to increase systematically...

Closure of "Effect of Bank Stability on Geometry of Gravel Rivers"

The interaction between flow and vegetation creates feedbacks to deposition that vary with channel velocity. This experimental study describes how channel velocity and stem-generated turbulence influence the deposition within and around an emergent patch of model vegetation, with a particular focus on deposition within the patch. The Reynolds number threshold for stem-scale turbulence generation was determined using velocity spectra and flow visualization. At high channel velocity resuspension occurred in the bare regions of the channel and a nonuniform spatial distribution of net deposition was observed around and within the patch. In contrast, at low channel velocity there was no (or limited) resuspension and a uniform distribution of net deposition was observed around and within the patch. The deposition inside the patch was enhanced, relative to a bare-channel control, only when the following two criteria were met: (1) the absence of stem turbulence, and (2) the presence of sediment resuspension in the bare channel. Comparison to previous lab and field studies further support these criteria.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2015WR018249

Sediment deposition within and around a finite patch of model vegetation over a range of channel velocity

Application of Structure-from-Motion photogrammetry in laboratory flumes

The international river interface cooperative: Public domain flow and morphodynamics software for education and applications

Numerical investigation of local scour at two adjacent cylinders

For the appropriate management and restoration of rivers, isolated vegetation is often a practical means for improving stream habitat and ecology. The effect of a finite vegetation patch on flow and bed morphology in an open channel was investigated using laboratory experiments. The patch containing emergent and submerged vegetation was modeled using circular cylinders and located mid-channel along a side wall. Several configurations of the patch and submergence ratio (i.e. water depth to the height of vegetation), and two flow conditions (i.e. below and above the sediment motion threshold) were considered. For flows below the sediment motion threshold, erosion occurred primarily on the opposite side of the patch and near the leading edge of the patch. The degree of scouring depth observed in both these regions was affected by the submergence ratio and it increased with the non-dimensional flow blockage (i.e. the product of the patch density and width). In contrast, for flows above the sediment motion threshold, sediment accumulated within and around the patch due to a reduction in bed shear stress, which was strongly influenced by the flow blockage and the obstruction ratio (i.e. the ratio of patch width to channel width). The eroded area observed within the patch was consistent with the interior adjustment region where the deceleration and diversion of flow occurred through the patch. As the flow blockage increased or as the obstruction ratio decreased, the deposition rate within and behind the patch decreased. Furthermore, the deposition rate increased with an increase in the ratio of flow rate through the patch to total flow rate regardless of the submergence ratio. Copyright © 2014 John Wiley & Sons, Ltd.

Bed morphological changes around a finite patch of vegetation.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2017WR021087

Numerical Simulation of Flow and Suspended Sediment Deposition Within and Around a Circular Patch of Vegetation on a Rigid Bed

Computational modeling of flow and morphodynamics through rigid-emergent vegetation

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.

https://research.aalto.fi/files/81291845/Flow_and_wake_characteristics_associated_with_riparian_vegetation_patches.pdf

Hyung Suk Kim

Papers

Numerical investigation of local scour at two adjacent cylinders

Bed morphological changes around a finite patch of vegetation.

Numerical Simulation of Flow and Suspended Sediment Deposition Within and Around a Circular Patch of Vegetation on a Rigid Bed

Computational modeling of flow and morphodynamics through rigid-emergent vegetation

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