Numerical study on river bar response to spatial variations of channel width

Duró, Gonzalo; Crosato, Alessandra; Tassi, Pablo

doi:10.1016/j.advwatres.2015.10.003

Cited by 64 publications

(84 citation statements)

References 42 publications

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“…Analytical theory shows that in the presence of a hydraulic forcing periodic bars forming close to the forcing correspond to hybrid bars, as opposed to free bars (Duró et al. ; Zolezzi and Seminara, ). Hybrid bars are longer than free bars and non‐migrating (Crosato and Saleh, ; Rodrigues et al.…”

Section: Discussionmentioning

confidence: 99%

“…While forced bars (Duró et al. ) are locally formed by a permanent finite deviation of the water flow resulting from an external factor (i.e. hydraulic forcing ), the initiation of periodic bars can be explained theoretically as a growing instability of the riverbed when the active channel width‐to‐depth ratio

β

exceeds a threshold

β_{cr}

(e.g.…”

Section: Introductionmentioning

confidence: 99%

“…Periodic bars can be characterized as free bars or hybrid bars (Duró et al. ). Free bars form in the absence of hydraulic forcing and are usually migrating (Tubino et al.…”

Section: Introductionmentioning

confidence: 99%

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Morphodynamics of alternate bars in the presence of riparian vegetation

Jourdain

Claude

Tassi

et al. 2020

Earth Surf Processes Landf

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Alpine gravel‐bed rivers are dynamic systems that have been subjected to many anthropic alterations in the past centuries. Riparian vegetation development on previously bare sediment bedforms has been a common adjustment, raising important management issues in terms of flood risks and biodiversity. Many of these rivers are also channelized, and as a result present a pattern of alternate bars. Considering recent advances in numerical biomorphodynamic modeling, this study aims at exploring numerically the morphodynamics of alternate bars in the presence of riparian vegetation. To this end, a dynamic vegetation module has been implemented on top of an existing morphodynamic model, accounting for ecological processes of seed dispersal, seedling recruitment, growth, and mortality. Numerical simulations have been performed on a simplified reach of a gravel‐bed river with free migrating alternate bars at initial state. In this work 96 scenarios have been simulated, each representing 50 years of channel evolution, with different flood regimes characterized by various peak discharges and flood durations. Yearly peak discharge variability is explicitly modeled in 48 scenarios. Model outcomes present two possible equilibrium biomorphodynamic behaviors: stationary vegetated bars, or free migrating bars in the case of frequent vegetation removal during floods. This binary behavior holds true when the stochasticity of annual peak discharges is represented, and for a wide range of parameter values included in vegetation dynamic modeling. Transient mobility of vegetated bars is observed in specific configurations where large sediment deposits deflect the flow field, eroding bar heads. Modeled bar wavelengths are in the range of values predicted for free bars by linear bar theory, and remain far from the theoretical values of hybrid, steady bars. The shift from unvegetated migrating bars to steady vegetated bars seems to show that in these simulations vegetation constitutes a hydraulic forcing, leading to a shift from free bars to forced bars, with a final configuration largely inherited from the initial state. © 2019 John Wiley & Sons, Ltd.

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Section: Discussionmentioning

confidence: 99%

β

exceeds a threshold

β_{cr}

(e.g.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Morphodynamics of alternate bars in the presence of riparian vegetation

Jourdain

Claude

Tassi

et al. 2020

Earth Surf Processes Landf

Self Cite

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“…(). In the following we will refer to these three approaches, respectively as ‘free‐bar predictor’ ‘hybrid‐bar predictor’ (Duró et al ., ) and ‘channel pattern predictor’. The free and the hybrid bar predictors are based on the linear solution of the complete 2D (depth‐averaged) morphodynamic equations for longitudinal and transverse momentum together with the continuity equations for water and sediments.…”

Section: Methodsmentioning

confidence: 99%

Channelization of a large Alpine river: what is left of its original morphodynamics?

Scorpio

Zen

Bertoldi

et al. 2018

Earth Surf Processes Landf

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The Adige River drains 12 200 km2 of the Eastern Alps and flows for 213 km within this mountain range. Similar to other large rivers in Central Europe, the Adige River was subject to massive channelization works during the 19th century. Thanks to the availability of several historical maps, this river represents a very valuable case study to document the extent to which the morphology of the river changed due to channelization and to understand how much is left of its original morphodynamics. The study was based on the analysis of seven sets of historical maps dating from 1803–1805 to 1915–1927, on geomorphological analysis, on the application of mathematical morphodynamic theories and on the application of bar and channel pattern prediction models. The study concerns 115 km of the main stem and 29 km of its tributaries. In the pre‐channelization conditions, the Adige River presented a prevalence of single‐thread channel planforms. Multi‐thread patterns developed only immediately downstream of the main confluences. During the 19th century, the Adige underwent considerable channel adjustment, consisting of channel narrowing, straightening, and reduction of bars and islands. Multi‐thread and single‐thread reaches evolved through different evolutionary trajectories, considering both the channel width and the bar/vegetation interaction. Bar and channel pattern predictors showed good correspondence with the observed patterns, including the development of multi‐thread morphologies downstream of the confluences. Application of the free‐bar predictor helped to interpret the strong reduction – almost complete loss – of exposed sediment bars after the channelization works, quantifying the riverbed inclination to form alternate bars. This morphological evolution can be observed in other Alpine rivers of similar size and similar massive channelization, therefore, a simplified conceptual model for large rivers subjected to channelization is proposed, showing that a relatively small difference in the engineered channel width may have a strong impact on the river dynamics, specifically on bar formation. Copyright © 2017 John Wiley & Sons, Ltd.

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“…We build from Snow and Slingerland (), Repetto et al (), Bolla Pittaluga et al (), Duró et al (), Blom et al (), and Ferrer‐Boix et al (), and begin our analysis with four assumptions: (1) a channel reach of at least 10–20

\overset{w}{true}

in length that has a well‐defined average bed surface slope; (2) statistical steady state conditions, defined as (a) bed topography adjustment rates that tend to zero across the reach and (b) comparability between the rates of total sediment supply ( Q ss ) and sediment flux ( Q sf ) between the upstream and downstream boundaries, respectively; (3) characteristic grain sizes of the bed surface D i that are tending to a spatially uniform condition; and (4) channel banks that change position at rates much less than those of bed elevation and bed surface sediment texture.…”

Section: Theory For the Local Channel Profilementioning

confidence: 99%

Morphodynamics of a Width‐Variable Gravel Bed Stream: New Insights on Pool‐Riffle Formation From Physical Experiments

et al. 2018

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Field observations, experiments, and numerical simulations suggest that pool‐riffles along gravel bed mountain streams develop due to downstream variations of channel width. Where channels narrow, pools are observed, and at locations of widening, riffles occur. Based on previous work, we hypothesize that the bed profile is coupled to downstream width variations through momentum fluxes imparted to the channel surface, which scale with downstream changes of flow velocity. We address this hypothesis with flume experiments understood through scaling theory. Our experiments produce pool‐riffle like structures across average Shields stresses τ∗ that are a factor 1.5–2 above the threshold mobility condition of the experimental grain size distribution. Local topographic responses are coupled to channel width changes, which drive flows to accelerate or decelerate on average, for narrowing and widening, respectively. We develop theory which explains the topography‐width‐velocity coupling as a ratio of two reinforcing timescales. The first timescale captures the time necessary to do work to the channel bed. The second timescale characterizes the relative time magnitude of momentum transfer from the flowing fluid to the channel bed surface. Riffle‐like structures develop where the work and momentum timescales are relatively large, and pools form where the two timescales are relatively small. We show that this result helps to explain local channel bed slopes along pool‐riffles for five data sets representing experimental, numerical, and natural cases, which span 2 orders of magnitude of reach‐averaged slope. Additional model testing is warranted.

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Numerical study on river bar response to spatial variations of channel width

Cited by 64 publications

References 42 publications

Morphodynamics of alternate bars in the presence of riparian vegetation

Morphodynamics of alternate bars in the presence of riparian vegetation

Channelization of a large Alpine river: what is left of its original morphodynamics?

Morphodynamics of a Width‐Variable Gravel Bed Stream: New Insights on Pool‐Riffle Formation From Physical Experiments

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