Study on the Migrating Speed of Free Alternate Bars

In-stream environments, many biogeochemical processes occur in the benthic biolayer, i.e., within sediments at a very shallow depth close to the sediment-water interface (SWI). These processes are important for stream ecology and the overall environment.Here, a 1D diffusive model is used to analyze the vertical exchange of solutes through the SWI and in the benthic biolayer. The model is applied to an extensive set of previously published laboratory experiments of solute exchange with different bed morphologies: flatbeds, dunes, and alternate bars. Although these different bed features induce mixing that is controlled by different physical processes at the SWI, overall mixing within the sediment is well represented by a parsimonious diffusive model, provided that the diffusivity profile declines exponentially with sediment depth.For all morphology types, mixing is better simulated by an exponential diffusivity model than a constant diffusivity approach. Two parameters define the exponential diffusivity model; the effective diffusivity at the SWI, and a depth scale over which the exponential profile decays. Using a combination of classification and regression trees (CART) and multiple linear regression approaches, we demonstrate that a single predictive model captures measured variability in the effective diffusivity coefficient at the SWI across all morphological types. The best predictive model for the decay depth scale, on the other hand, is tailored to each morphological type separately.The predictive framework developed here contributes to our understanding of the physical processes responsible for mixing across the SWI, &#160;and therefore the in-bed processes that contribute to the biogeochemical processing of nutrients and other contaminants in streams.

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Flume experiments on vegetated alternate bars

E3S Web of Conferences ◽

10.1051/e3sconf/20184002034 ◽

2018 ◽

Vol 40 ◽

pp. 02034 ◽

Cited By ~ 1

Author(s):

Giulio Calvani ◽

Simona Francalanci ◽

Luca Solari

Keyword(s):

Hydrological Regime ◽

Spatial Arrangement ◽

Flume Experiments ◽

Rigid Vegetation ◽

Hydraulic Conditions ◽

Laboratory Flume ◽

Alternate Bars ◽

River Reach ◽

Bed Slope ◽

And Migration

The planform morphology of a river reach is the result of the combined actions of sediment motion (erosion, transport and deposition), hydrological regime, development and growth of vegetation. However, the interactions among these processes are still poorly understood and rarely investigated in laboratory flume experiments. In these experiments and also in numerical modelling, vegetation is usually represented by rigid cylinders, although it is widely recognized that this schematization cannot reproduce the effects of root stabilization and binding on riverbed sediment. In this work, we focus on the effects of added vegetation on morphological dynamics of alternate bars in a straight channel by means of flume experiments. We performed laboratory experiments reproducing hydraulic conditions that are typical of gravel bed rivers, in terms of water depth, bed slope and bed load; these conditions led to the formation of freely migrating alternate bars. We then employed rigid vegetation that was deployed on the reproduced alternate bars according to field observations. Various vegetation scenarios, in terms of density and spatial arrangement, were deployed in the flume experiments such to mimic different maintenance strategies. Results show the effects of rigid vegetation on the alternate bar configuration on the overall topographic pattern, the main alternate bar characteristics (such as amplitude and wavelength) and migration rate.

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Numerical Modelling of Alternate Bars in Shallow Channels

Braided Rivers ◽

10.1002/9781444304374.ch7 ◽

2009 ◽

pp. 153-175 ◽

Cited By ~ 7

Author(s):

A. Bernini ◽

V. Caleffi ◽

A. Valiani

Keyword(s):

Numerical Modelling ◽

Alternate Bars

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Parametric transitions between bare and vegetated states in water-driven patterns

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1721765115 ◽

2018 ◽

Vol 115 (32) ◽

pp. 8125-8130 ◽

Cited By ~ 12

Author(s):

Matteo Bernard Bertagni ◽

Paolo Perona ◽

Carlo Camporeale

Keyword(s):

Sediment Transport ◽

Pattern Formation ◽

Stochastic Processes ◽

Vegetation Dynamics ◽

Floquet Theory ◽

Center Manifold ◽

Natural Origin ◽

Physical Conditions ◽

Alternate Bars ◽

Transport Flow

Conditions for vegetation spreading and pattern formation are mathematically framed through an analysis encompassing three fundamental processes: flow stochasticity, vegetation dynamics, and sediment transport. Flow unsteadiness is included through Poisson stochastic processes whereby vegetation dynamics appears as a secondary instability, which is addressed by Floquet theory. Results show that the model captures the physical conditions heralding the transition between bare and vegetated fluvial states where the nonlinear formation and growth of finite alternate bars are accounted for by Center Manifold Projection. This paves the way to understand changes in biogeomorphological styles induced by man in the Anthropocene and of natural origin since the Paleozoic (Devonian plant hypothesis).

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Numerical Study of Alternate Bars in Alluvial Channels With Nonuniform Sediment

Water Resources Research ◽

10.1029/2017wr022420 ◽

2019 ◽

Vol 55 (4) ◽

pp. 2976-3003 ◽

Cited By ~ 9

Author(s):

F. Cordier ◽

P. Tassi ◽

N. Claude ◽

A. Crosato ◽

S. Rodrigues ◽

...

Keyword(s):

Numerical Study ◽

Alluvial Channels ◽

Nonuniform Sediment ◽

Alternate Bars

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