Taking the river inside: Fundamental advances from laboratory experiments in measuring and understanding bedload transport processes

Yager, E.; Kenworthy, M.; Monsalve, Angel

doi:10.1016/j.geomorph.2015.04.002

Cited by 34 publications

(44 citation statements)

References 127 publications

(199 reference statements)

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“…Still little is known on the behavior of an armor under peak flow (Vericat et al, 2006;Yager et al, 2015). Studies have demonstrated that, during peak flow, armored surfaces can be stable and persist or broken and reform during the waning phase of the flood event.…”

Section: Introductionmentioning

confidence: 99%

Armor breakup and reformation in a degradational laboratory experiment

2016

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Abstract. Armor breakup and reformation was studied in a laboratory experiment using a trimodal mixture composed of a 1 mm sand fraction and two gravel fractions (6 and 10 mm). The initial bed was characterized by a stepwise downstream fining pattern (trimodal reach) and a downstream sand reach, and the experiment was conducted under conditions without sediment supply. In the initial stage of the experiment an armor formed over the trimodal reach. The formation of the armor under partial transport conditions led to an abrupt spatial transition in the bed slope and in the mean grain size of the bed surface, as such showing similar results to a previous laboratory experiment conducted with a bimodal mixture. The focus of the current analysis is to study the mechanisms of armor breakup. After an increase in flow rate the armor broke up and a new coarser armor quickly formed. The breakup initially induced a bed surface fining due to the exposure of the finer substrate, which was accompanied by a sudden increase in the sediment transport rate, followed by the formation of an armor that was coarser than the initial one. The reformation of the armor was enabled by the supply of coarse material from the upstream degrading reach and the presence of gravel in the original substrate sediment. Here armor breakup and reformation enabled slope adjustment such that the new steady state was closer to normal flow conditions.

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Section: Introductionmentioning

confidence: 99%

Armor breakup and reformation in a degradational laboratory experiment

2016

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“…Yager et al. () proposed several key areas to further investigate sediment transport in gravel‐bed rivers under unsteady conditions, including the scaling of experimental hydrographs, and isolating the influence of different hydrograph characteristics on bedload transport processes. At present, there appears to be little consensus in the literature regarding the appropriate scaling of experimental hydrographs, particularly the duration.…”

Section: Discussionmentioning

confidence: 99%

Evolution of gravel surfaces in a sediment‐recirculating flume

Qin

Zhong

et al. 2017

Earth Surf Processes Landf

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The assumption of the equilibrium state of gravel surfaces in flume experiments under feeding or recirculating conditions is generally justified by three equilibrium criteria based on sediment transport, slopes, and bed features. When these parameters become stable, an experiment is expected to reach equilibrium. This equilibrium state, however, is based on a one‐dimensional model, the Exner equation, which may not truly reflect the equilibrium state of the system considering the complex flow and sediment processes. In this paper, the evolutionary process of a gravel surface is investigated based on a large‐scale recirculating flume experiment. The performances of the three equilibrium criteria are evaluated first, and then the evolution of the bed morphology is studied. The key findings include the following: (1) the sediment transport rate, slopes of water and bed surfaces, and one‐dimensional morphological features reach equilibrium roughly simultaneously; (2) two‐dimensional morphology continually evolves after these characteristics reach equilibrium, which is confirmed by the characteristics of the sediment transport process; and (3) the results from a numerical simulation suggest that a much longer time is required to reach an equilibrium state. Our results suggest that sufficient experimental time is required to investigate the equilibrium morphological characteristics of gravel surfaces, which is much longer than the equilibrium time reflected by the one‐dimensional equilibrium criteria. Copyright © 2017 John Wiley & Sons, Ltd.

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“…This notion of threshold is often criticized and might not exist when considering a stochastic sediment transport (Einstein, ; Lavelle and Mofjeld, ; Yager et al. ). The frictional force exerted by the flow is referred to as the bed shear stress .…”

Section: Introductionmentioning

confidence: 99%

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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Taking the river inside: Fundamental advances from laboratory experiments in measuring and understanding bedload transport processes

Cited by 34 publications

References 127 publications

Armor breakup and reformation in a degradational laboratory experiment

Armor breakup and reformation in a degradational laboratory experiment

Evolution of gravel surfaces in a sediment‐recirculating flume

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

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