Diffusive evolution of experimental braided rivers

Reitz, M. D.; Jerolmack, D. J.; Lajeunesse, É.; Limare, Angela; Devauchelle, Olivier; Métivier, François

doi:10.1103/physreve.89.052809

Cited by 25 publications

(42 citation statements)

References 41 publications

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“…Parker's model (Parker (1978a)) predicted τ * bf /τ * c ≈ 1.2 for equilibrium bed-load rivers, in agreement with observations of natural gravel-bed rivers (Paola et al (1992); Parker et al (1998); Dade and Friend (1998);Parker et al (2007); Phillips and Jerolmack (2016)) and laboratory experiments (Ikeda et al (1988); Pitlick et al (2013); Reitz et al (2014)). In terms of the regime equations 1, gravel-bed rivers thus follow expectations from the threshold theory but with a slight offset due to their higher bankfull Shields stress (Métivier et al (2017)).…”

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confidence: 82%

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Evidence of, and a Proposed Explanation for, Bimodal Transport States in Alluvial Rivers

Dunne¹,

Jerolmack²

2017

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Abstract. Gravel-bedded rivers organize their bankfull channel geometry and grain size such that shear stress is close to the threshold of motion. Sand-bedded rivers on the other hand typically maintain bankfull fluid stresses far in excess of threshold, a condition for which there is no satisfactory understanding. A fundamental question arises: Are bed-load (gravel-bedded) and suspension (sand-bedded) rivers two distinct equilibrium states, or do alluvial rivers exhibit a continuum of transport regimes as some have recently suggested? We address this question in two ways: (1) re-analysis of global channel geometry datasets, 5 with consideration of the dependence of critical shear stress upon site-specific characteristics (e.g. slope and grain size); and (2) examination of a longitudinal river profile as it transits from gravel to sand-bedded. Data reveal that the transport state of alluvial river-bed sediments is bimodal, showing either near-threshold or suspension conditions, and that these regimes correspond to the respective bimodal peaks of gravel and sand that comprise natural river-bed sediments. Sand readily forms near-threshold channels in the laboratory and some field settings, however, indicating that another factor, such as bank cohesion, must be 10 responsible for maintaining suspension channels. We hypothesize that alluvial rivers adjust their geometry to the thresholdlimiting bed and bank material -which for gravel-bedded rivers is gravel, but for sand-bedded rivers is mud (if present) -and present tentative evidence for this idea.

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confidence: 82%

“…Channels formed by seepage erosion in sand (Devauchelle et al (2011)) are observed to transport sand as bedload and, like gravel bedload rivers, cluster approximately at the threshold of motion. Similarly, sand-bedded rivers in laboratory experiments also form near-threshold channels (Reitz et al (2014); Métivier et al (2016);Federici and Paola (2003)). …”

mentioning

confidence: 80%

Evidence of, and a Proposed Explanation for, Bimodal Transport States in Alluvial Rivers

Dunne¹,

Jerolmack²

2017

Preprint

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“…In sand-bed rivers, the geometry of braided threads appears to be indistinguishable from that of meandering ones. This observation accords with recent laboratory experiments Reitz et al, 2014). To our knowledge, this similarity has not been fully investigated in gravel-bed rivers.…”

supporting

confidence: 78%

“…If confirmed, this would suggest that a braid results from the collective behavior of individual threads, the property and dynamics of which would be close to that of meandering threads (Sinha and Friend, 1994;Ashmore, 2013;Reitz et al, 2014).…”

Section: Resultsmentioning

confidence: 99%

Geometry of meandering and braided gravel-bed threads from the Bayanbulak Grassland, Tianshan, P. R. China

Métivier¹,

Devauchelle

Chauvet

et al. 2016

Earth Surf. Dynam.

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Abstract. The Bayanbulak Grassland, Tianshan, P. R. China, is located in an intramontane sedimentary basin where meandering and braided gravel-bed rivers coexist under the same climatic and geological settings. We report and compare measurements of the discharge, width, depth, slope and grain size of individual threads from these braided and meandering rivers. Both types of threads share statistically indistinguishable regime relations. Their depths and slopes compare well with the threshold theory, but they are wider than predicted by this theory. These findings are reminiscent of previous observations from similar gravel-bed rivers. Using the scaling laws of the threshold theory, we detrend our data with respect to discharge to produce a homogeneous statistical ensemble of width, depth and slope measurements. The statistical distributions of these dimensionless quantities are similar for braided and meandering threads. This suggests that a braided river is a collection of intertwined threads, which individually resemble those of meandering rivers. Given the environmental conditions in Bayanbulak, we furthermore hypothesize that bedload transport causes the threads to be wider than predicted by the threshold theory.

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“…It is thus reasonable to assume that the deposit inherits the slope of the channels that built it. The way a river selects its morphology is still a matter of debate, but it has been recently pointed out that most laboratory rivers, including those flowing over an experimental fan, remain near the threshold for sediment transport (Reitz and Jerolmack, 2012;Seizilles et al, 2013;Reitz et al, 2014;Métivier et al, 2017). Assuming a channel is exactly at threshold yields a theoretical relationship between its water discharge and its slope (Glover and Florey, 1951;Hen- derson, 1961).…”

Section: Mass Balancementioning

confidence: 99%

Self-similar growth of a bimodal laboratory fan

et al. 2017

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Abstract.Using laboratory experiments, we investigate the growth of an alluvial fan fed with two distinct granular materials. Throughout the growth of the fan, its surface maintains a radial segregation, with the less mobile sediment concentrated near the apex. Scanning the fan surface with a laser, we find that the transition between the proximal and distal deposits coincides with a distinct slope break. A radial cross section reveals that the stratigraphy records the signal of this segregation. To interpret these observations, we conceptualize the fan as a radially symmetric structure that maintains its geometry as it grows. When combined with slope measurements, this model proves consistent with the sediment mass balance and successfully predicts the slope of the proximal-distal transition as preserved in the fan stratigraphy. While the threshold-channel theory provides an order-of-magnitude estimate of the fan slopes, driven by the relatively high sediment discharge in our experimental system, the actual observed slopes are 3-5 times higher than those predicted by this theory.

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Diffusive evolution of experimental braided rivers

Cited by 25 publications

References 41 publications

Evidence of, and a Proposed Explanation for, Bimodal Transport States in Alluvial Rivers

Evidence of, and a Proposed Explanation for, Bimodal Transport States in Alluvial Rivers

Geometry of meandering and braided gravel-bed threads from the Bayanbulak Grassland, Tianshan, P. R. China

Self-similar growth of a bimodal laboratory fan

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