Self-similar growth of a bimodal laboratory fan

Delorme, Pauline; Voller, V. R.; Paola, Chris; Devauchelle, Olivier; Lajeunesse, É.; Barrier, Laurie; Métivier, François

doi:10.5194/esurf-5-239-2017

Cited by 19 publications

(27 citation statements)

References 54 publications

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“…We believe that this suggests that the size of the largest sediment in the bed may determine the deposition threshold for a mixture, at least for those situations in which competence controls sediment deposition, not sediment transport capacity. The implication of which is that the gradient of self-formed alluvial deposits is likely to be related to the mobility of the largest sediment in transport not the median grain size, as evidenced in bimodal fan experiments (Reitz and Jerolmack, 2012;Delorme et al, 2017).…”

Section: Differential Mobilitymentioning

confidence: 99%

“…We know that surficial adjustment, bedforms, and macroforms modulate bed material sediment transport rate, acting to dissipate energy and provide stability to the overall channel (Cherkauer, 1973;Montgomery and Buffington, 1997;Venditti et al, 2017). For example, it has been thought that grains may stabilise through rotation (Masteller and Finnegan, 2017), their organisation into cells (Church et al, 1998;Monsalve and Yager, 2017), and the formation of alternate bars and patches (Lisle et al, 1991;Dietrich et al, 2006;Nelson et al, 2010). One of the most well studied of these adjustment phenomena is the coarsening of the bed surface due to the preferential removal of fines or their kinetic sieving into the subsurface, until an armour layer develops that approximately equalises the threshold entrainment stress of the bed (Parker and Klingeman, 1982;Parker et al, 1982b;Andrews, 1983).…”

Section: Introductionmentioning

confidence: 99%

“…One of the most well studied of these adjustment phenomena is the coarsening of the bed surface due to the preferential removal of fines or their kinetic sieving into the subsurface, until an armour layer develops that approximately equalises the threshold entrainment stress of the bed (Parker and Klingeman, 1982;Parker et al, 1982b;Andrews, 1983). Armour may develop in both sediment-starved reaches as static armour (Sutherland, 1987;Dietrich et al, 1989;Parker and Sutherland, 1990;Kondolf, 1997;Vericat et al, 2006;Nelson et al, 2009) or where sediment supply is present as a mobile armour layer (Parker and Klingeman, 1982;Andrews and Parker, 1987;Parker, 1990). It is the formation of an armour layer that prevents continued transport of the material and stabilises the channel against further deformative work.…”

Section: Introductionmentioning

confidence: 99%

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Stabilising large grains in self-forming steep channels

Booker

Eaton

2020

Earth Surf. Dynam.

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Abstract. It is understood that the interaction between sediment supply and discharge drives first-order behaviour of alluvial deposits. The influence of the grain size distribution over the mobility and resultant evolution is, however, unclear. Four experiments were conducted in a scaled physical model for two grain size distributions, analogous to a one-dimensional self-formed alluvial fan. We demonstrate the unsuitability of the median grain size as a predictor of deposit behaviour at flows when the material is not equally mobile. The results instead suggest, during conditions of unequal mobility, that the largest grains control the transport efficiency of the overall sediment mixture, and thus also the morphodynamics of the deposit and its tendency to store or evacuate material. Deposits appear to show a dependence upon the rate of material supply more strongly when the likelihood of its motion is less equally distributed (i.e. under partial transport conditions). If the coarse fraction (e.g. greater than 84th percentile) is instead mobile due to increased discharge or because of their relative size, transport rates will increase and the behaviour of the mixtures converge to a common state, with morphology influenced by the material's mobility.

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Section: Differential Mobilitymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Stabilising large grains in self-forming steep channels

Booker

Eaton

2020

Earth Surf. Dynam.

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“…A sediment transport law was calibrated to compare the experimental results with theory using the methods of Seizilles et al (2013) and Delorme et al (2017). A series of runs were carried out with constant water and sediment feed rates in a 3 cm wide flume.…”

Section: Sediment Transport Lawmentioning

confidence: 99%

Experimental evidence for bifurcation angles control on abandoned channel fill geometry

2020

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Abstract. The nature of abandoned channels' sedimentary fills has a significant influence on the development and evolution of floodplains and ultimately on fluvial reservoir geometry. A control of bifurcation geometry (i.e., bifurcation angle) on channel abandonment dynamics and resulting channel fills, such as sand plugs, has been intuited many times but never quantified. In this study, we present a series of experiments focusing on bedload transport designed to test the conditions for channel abandonment by modifying the bifurcation angle between channels, the flow incidence angles and the differential channel bottom slopes. We find that disconnection is possible in the case of asymmetrical bifurcations with high diversion angle (≥30∘) and quantify for the first time an inverse relationship between diversion angle and sand plug length and volume. The resulting sand plug formation is initiated in the flow separation zone at the external bank of the mouth of the diverted channel. Sedimentation in this zone induces a feedback loop leading to sand plug growth, discharge decrease and eventually to channel disconnection. Finally, the formation processes and final complex architecture of sand plugs are described, allowing for a better understanding of their geometry. Although our setup lacks some of the complexity of natural rivers, our results seem to apply at larger scales. Taken into account, these new data will improve fluvial (reservoir) models by incorporating more realistic topography and grain size description in abandoned channels.

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“…A sediment transport law was calibrated to compare the experimental results with theory using the methods of Seizilles 2013and Delorme et al, (2017). A series of runs were carried out with constant water and sediment feed rates in a 3cmwide flume.…”

Section: Sediment Transport Lawmentioning

confidence: 99%

Experimental evidences for bifurcation angles control on abandoned channel fill geometry

Szewczyk¹,

Grimaud²,

Cojan³

2020

Preprint

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Abstract. The nature of abandoned channels sedimentary fills has a significant influence on the development and evolution of floodplains and ultimately on fluvial reservoir geometry. A control of bifurcation geometry (i.e., bifurcation angle) on channel abandonment dynamics and resulting channel fills, such as sandplug, has been intuited many times but never quantified. In this study we present a series of experiments focusing on bedload transport designed to test the conditions for channel abandonment by modifying the bifurcation angle between channels, the flow incidence angles and the differential channel bottom slopes. We find that disconnection is possible in the case of asymmetrical bifurcations with high diversion angle (≥ 30°) and quantify for the first time a relationship between diversion angle and sandplug length and volume. The resulting sandplug formation is initiated in the flow separation zone at the external bank of the mouth of the diverted channel. Sedimentation in this zone initiates a feedback loop leading to sandplug growth, discharge decrease and eventually to channel disconnection. Finally, the formation processes and final complex architecture of sandplugs are described, allowing for a better understanding of their geometry. Although our setup lacks the complexity of natural rivers, our results seem to apply at larger scales. Taken into account, these new data will improve the realism of fluvial models.

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Self-similar growth of a bimodal laboratory fan

Cited by 19 publications

References 54 publications

Stabilising large grains in self-forming steep channels

Stabilising large grains in self-forming steep channels

Experimental evidence for bifurcation angles control on abandoned channel fill geometry

Experimental evidences for bifurcation angles control on abandoned channel fill geometry

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