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

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

“…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 ).…”

“…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, ).…”

“…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, ).…”

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

“…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 . 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).…”

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