Dimensionless critical shear stress in gravel-bed rivers

Petit, François; Houbrechts, Geoffrey; Peeters, Alexandre; Hallot, Éric; Campenhout, Jean Van; Denis, Anne-Cécile

doi:10.1016/j.geomorph.2015.09.008

Cited by 47 publications

(16 citation statements)

References 93 publications

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“…It should be recalled that the total bed shear stress can be broken down into a bed shear stress component due to grain resistance, g , and a bed shear stress component due to form resistance, f . Sediment motion is generally attributed to the skin friction g and not to the total shear stress (Petit et al, 2015). To further investigate the part of bed forms in the scatter of our data and focus on grain scale, we estimate the skin friction to analyze sediment transport rate in our experiments.…”

Section: Impact Of Bed Arrangementmentioning

confidence: 99%

Transport of moderately sorted gravel at low bed shear stresses: The role of fine sediment infiltration

Perret

Berni

Camenen

et al. 2018

Earth Surf Processes Landf

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A reliable estimation of sediment transport in gravel‐bed streams is important for various practical engineering and biological studies (e.g., channel stability design, bed degradation/aggradation, restoration of spawning habitat). In the present work, we report original laboratory experiments investigating the transport of gravel particles at low bed shear stresses. The laboratory tests were conducted under unsteady flow conditions inducing low bed shear stresses, with detailed monitoring of the bed topography using a laser scanner. Effects of bed surface arrangements were documented by testing loose and packed bed configurations. Effects of fine sediments were examined by testing beds with sand, artificial fine sand or cohesive silt infiltrated in the gravel matrix. Analysis of the experimental data revealed that the transport of gravel particles depends upon the bed arrangement, the bed material properties (e.g., size and shape, consolidation index, permeability) and the concentration of fine sediments within the surface layer of moving grains. This concentration is directly related to the distribution of fine particles within the gravel matrix (i.e., bottom‐up infiltration or bridging) and their transport mode (i.e., bedload or suspended load). Compared to loose beds, the mobility of gravel is reduced for packed beds and for beds clogged from the bottom up with cohesive fine sediments; in both cases, the bed shear stress for gravel entrainment increases by about 12%. On the other hand, the mobility of gravel increases significantly (bed shear stress for particle motion decreasing up to 40%) for beds clogged at the surface by non‐cohesive sand particles. Copyright © 2017 John Wiley & Sons, Ltd.

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Section: Impact Of Bed Arrangementmentioning

confidence: 99%

Transport of moderately sorted gravel at low bed shear stresses: The role of fine sediment infiltration

Perret

Berni

Camenen

et al. 2018

Earth Surf Processes Landf

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“…These differences can be explained by one of the following reasons, assuming that the chosen model (Equation ) represents correctly the physical processes involved in bedload transport: (i) they are a result of the wrong estimation of the dimensionless effective bed shear stress

τ_{e}^{*}

, which is the only parameter controlling bedload dynamics according to the literature (Petit et al. ); with a better estimation, a difference in the (

q_{s}^{*}, τ_{e}^{*} false/ τ_{ref}^{*}

) relationships should no longer be observed; or (ii) the force exerted by the flow (represented by

τ_{e}^{*}

) is not the only one driving the bedload dynamics; bed stability also controls directly the transport rate; or (iii) both of the previous reasons. One should keep in mind that

D_{50}

and

D_{84}

(i.e.…”

Section: Resultsmentioning

confidence: 99%

“…According to the literature, it can be assimilated into the shear stress at the grain scale

τ_{g}

(Einstein, ; Petit et al. ). The excess of drag due to bedforms is considered as not contributing to gravel transport.…”

Section: Methodsmentioning

confidence: 99%

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How does the bed surface impact low‐magnitude bedload transport rates over gravel‐bed rivers?

Perret

Berni

Camenen

2020

Earth Surf Processes Landf

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Bedload transport is a complex phenomenon that is not well understood, especially for poorly sorted sediment and low transport rates, which is what is typically found in alpine gravel‐bed rivers. In this paper, the interaction between bedload rate, bed stability and flow is investigated using flume experiments. Significant differences in bedload rates were observed for experiments conducted on beds formed with the same gravel material but presenting diverse arrangements and bedforms. Tests were performed under regimes of low transport rate, which are mainly controlled by gravel‐bed roughness. Different scales of roughness were identified using the statistical characteristics of detailed bed elevation measurements: grain, structure and large bedform scales. The role played by these different roughness scales in bedload dynamics was examined. For quasi‐flat beds, bed stability was quantified using a combination of bed surface criteria describing grain and structure scales. It was found that bed stability affects the bedload rate directly and not only through its influence on the flow or on the incipient motion. For beds with large bedforms, the analysis of bedload dynamics also showed the importance of accounting for effective bed shear stress distributions. An empirical bedload model for low transport regimes was suggested. Compared with previous formulae developed for alpine rivers, this model accounts for bed stability and distribution of effective bed shear stress. It significantly improves the understanding of gravel dynamics over complex beds such as arranged beds or those with large bedforms. However, further tests are needed to use the model outside the range of conditions of this study. © 2019 John Wiley & Sons, Ltd.

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“…Critical shear stress establishes a threshold for the entrainment of particles depending on their size (D50, median diameter), with larger sizes requiring higher shear stresses for their mobilization (Powell, ). Petit et al () observed mobilization of gravels of 28 mm (D50) in the Eau Blanche River (France) with a shear stress value of 14 N/m 2 . Yet, surface‐based transport models for gravel predominant substrates by Wilcock and Crowe (), and then revised by De Linares and Belleudy (), indicate 14 N/m 2 as a reference shear stress for the mobilization of particle sizes up to 30 mm (D50, median diameter).…”

Section: Methodsmentioning

confidence: 99%

Targeting lateral connectivity and morphodynamics in a large river‐floodplain system: The upper Rhine River

Diáz-Redondo

Egger

Marchamalo

et al. 2018

River Research & Apps

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As a consequence of historical damming and channelization, most large rivers are disconnected from their floodplains, which therefore endure severe deficits in fluvial dynamics. Regaining some degree of lateral connectivity can lead to improved geomorphological and biological interactions. Yet, it is necessary to take into account limitations posed by current uses and legislation. This study presents a methodological approach to the selection of a realistic restoration target for a heavily modified large river segment, the free-flowing Upper Rhine River downstream of Iffezheim dam (France-Germany border), based on the analysis of the existing biogeomorphic deficits, constraints set by human uses, and previous restoration experiences. To achieve the selected restoration target, proposed scenarios include embankment removal, bank lowerings, and side channel widenings with the aim of increasing lateral hydrological connectivity and promoting morphodynamics (bank erosion in lateral channels) that allow for the renewal of floodplain habitats. Results from 2-D hydraulic simulations allow for a sensitivity analysis, comparing the current situation with the proposed scenarios, through parameters such as shore length of side channels actively connected at both ends to the main channel (eupotamon), and shear stress as a proxy for initiation of gravel erosion. Outcomes indicate that the two proposed restoration scenarios would succeed in reconnecting side channels and in increasing areas prone to substrate erosion, while maintaining flood protection and the heaviest navigation use among European rivers. The presented approach aids in the assessment of potential large river restoration scenarios and, thus, in the discussion of water management strategies.

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Dimensionless critical shear stress in gravel-bed rivers

Cited by 47 publications

References 93 publications

Transport of moderately sorted gravel at low bed shear stresses: The role of fine sediment infiltration

Transport of moderately sorted gravel at low bed shear stresses: The role of fine sediment infiltration

How does the bed surface impact low‐magnitude bedload transport rates over gravel‐bed rivers?

Targeting lateral connectivity and morphodynamics in a large river‐floodplain system: The upper Rhine River

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