Comparison of four methods to calculate aeolian sediment transport threshold from field data: Implications for transport prediction and discussion of method evolution

Barchyn, Thomas E.; Hugenholtz, Chris H.

doi:10.1016/j.geomorph.2011.01.022

Cited by 40 publications

(30 citation statements)

References 60 publications

(104 reference statements)

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“…Our results build on the statistical TFEM (Stout & Zobeck, ) to provide the first field‐based derivation of separate fluid and impact thresholds in aeolian saltation. Though fluid and impact thresholds for saltation initiation and cessation have long been theorized (e.g., Bagnold, ; Kok, ) and measured in wind tunnel experiments (e.g., Chepil, ; Iversen & Rasmussen, ), the difficulty of directly measuring threshold crossings in the field (e.g., Barchyn & Hugenholtz, ) has limited the ability of past studies to resolve both thresholds. To overcome these limitations, we hypothesized, based on observations (Figure ), that the relative contributions of fluid and impact thresholds in controlling saltation occurrence vary systematically with the frequency of saltation transport (equation ).…”

Section: Discussionmentioning

confidence: 99%

“…Despite this evidence supporting the existence of dual thresholds, we consider aspects of our methodology that could produce an artificial variation in effective threshold with saltation activity. First, our measured thresholds could depend on the selection of averaging intervals δt (Figure ; Barchyn & Hugenholtz, ; Schönfeldt, ; Stout, ; Wiggs, Atherton, & Baird, ). Saltation is more likely to occur within longer δt increments (Figure b), thus increasing f Q (Figure c; Sherman et al, ).…”

Section: Discussionmentioning

confidence: 99%

“…Despite the central importance of the saltation threshold in predicting sand and dust fluxes, there remains a lack of agreement over the best way to model or even measure this threshold (Barchyn & Hugenholtz, ). Most predictive equations for saltation usually include only a single threshold value (Barchyn, Martin, et al, ).…”

Section: Introductionmentioning

confidence: 99%

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Distinct Thresholds for the Initiation and Cessation of Aeolian Saltation From Field Measurements

2018

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Wind‐blown sand and dust models depend sensitively on the threshold wind stress. However, laboratory and numerical experiments suggest the coexistence of distinct fluid and impact thresholds for the initiation and cessation of aeolian saltation, respectively. Because aeolian transport models typically use only a single threshold, existence of separate higher fluid and lower impact thresholds complicates the prediction of wind‐driven transport. Here we extend the statistical Time Frequency Equivalence Method to derive the first field‐based estimates of distinct fluid and impact thresholds from high‐frequency wind and saltation measurements at three field sites. Our measurements show that when saltation is mostly inactive, its instantaneous occurrence is governed primarily by wind exceedance of the fluid threshold. As saltation activity increases, so too does the relative importance of the impact threshold, until it dominates under near‐continuous transport conditions. Although both thresholds are thus important for high‐frequency saltation prediction, our results suggest that the time‐averaged saltation flux is primarily governed by the impact threshold.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Distinct Thresholds for the Initiation and Cessation of Aeolian Saltation From Field Measurements

2018

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“…The overarching problem associated with the rather poor current knowledge of aeolian sediment transport initiation in the field (see open problems above) is that, to the authors' knowledge, there are no direct field measurements of the transport initiation threshold

{normalΘ}_{t}^{In}

. In fact, existing field experiments have focused on detecting aeolian saltation transport (Barchyn and Hugenholtz, , and references therein) rather than on how the fluid entrainment of individual bed particles, which usually starts out as a rolling motion, leads to saltation transport. Hence, we currently do neither know the wind speeds that are required in the field to initiate rolling transport of individual bed particles nor whether such rolling transport, like in wind tunnels, always evolves into saltation transport (see open problems above).…”

Section: Fluid Entrainment By Turbulent Flowsmentioning

confidence: 99%

“…Hence, we currently do neither know the wind speeds that are required in the field to initiate rolling transport of individual bed particles nor whether such rolling transport, like in wind tunnels, always evolves into saltation transport (see open problems above). What adds to the problem is that existing field studies either obtain saltation transport threshold estimates using methods that do not seek to distinguish saltation transport initiation and cessation (Barchyn and Hugenholtz, , and references therein) or assume that

{normalΘ}_{t}^{In}

coincides with the continuous saltation transport threshold (Martin and Kok, ) (which is a controversial assumption, see section ).…”

Section: Fluid Entrainment By Turbulent Flowsmentioning

confidence: 99%

The Physics of Sediment Transport Initiation, Cessation, and Entrainment Across Aeolian and Fluvial Environments

Pähtz

Clark

Valyrakis

et al. 2020

Reviews of Geophysics

129

149

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Predicting the morphodynamics of sedimentary landscapes due to fluvial and aeolian flows requires answering the following questions: Is the flow strong enough to initiate sediment transport, is the flow strong enough to sustain sediment transport once initiated, and how much sediment is transported by the flow in the saturated state (i.e., what is the transport capacity)? In the geomorphological and related literature, the widespread consensus has been that the initiation, cessation, and capacity of fluvial transport, and the initiation of aeolian transport, are controlled by fluid entrainment of bed sediment caused by flow forces overcoming local resisting forces, whereas aeolian transport cessation and capacity are controlled by impact entrainment caused by the impacts of transported particles with the bed. Here the physics of sediment transport initiation, cessation, and capacity is reviewed with emphasis on recent consensus‐challenging developments in sediment transport experiments, two‐phase flow modeling, and the incorporation of granular physics' concepts. Highlighted are the similarities between dense granular flows and sediment transport, such as a superslow granular motion known as creeping (which occurs for arbitrarily weak driving flows) and system‐spanning force networks that resist bed sediment entrainment; the roles of the magnitude and duration of turbulent fluctuation events in fluid entrainment; the traditionally overlooked role of particle‐bed impacts in triggering entrainment events in fluvial transport; and the common physical underpinning of transport thresholds across aeolian and fluvial environments. This sheds a new light on the well‐known Shields diagram, where measurements of fluid entrainment thresholds could actually correspond to entrainment‐independent cessation thresholds.

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Grains in Motion

Baas

2019

Aeolian Geomorphology

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Comparison of four methods to calculate aeolian sediment transport threshold from field data: Implications for transport prediction and discussion of method evolution

Cited by 40 publications

References 60 publications

Distinct Thresholds for the Initiation and Cessation of Aeolian Saltation From Field Measurements

Distinct Thresholds for the Initiation and Cessation of Aeolian Saltation From Field Measurements

The Physics of Sediment Transport Initiation, Cessation, and Entrainment Across Aeolian and Fluvial Environments

Grains in Motion

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