Vertical profiles of aeolian mass flux above different sand surfaces and sand surfaces covered with pebbles

Remote Observations of Aeolian Saltation

“…Instead, measurements in this present study collectively suggest that H gradually increases with increasing shear up to at least an average u* of 0.76 m/s when assuming log shaped wind profiles. The inconsistency in the conclusions between Martin and Kok (2017) and this present study could be related to and Dłużewski (2022) found that H scaled with u. Interestingly, they found a relatively limited response to H on sandy beds for ∼7 m/s < u < 11 m/s. However, sediment beds with high fractions of pebbles had both a larger average H and exhibited a larger proportional increase in H per unit increase in u, relative to sandy beds.…”

“…The inconsistency in the conclusions between Martin and Kok (2017) and this present study could be related to the following factors: (a) the FRF site is a coastal beach with wide heterogeneity in bed sediments (e.g., Cohn et al., 2022); (b) sparse in situ sensors in previous works leading to limitations in deriving comprehensive trends in the vertical structure of the saltation layer at sufficient resolution; (c) masking of trends due to large averaging intervals; (d) differing definitions for H ; and/or (e) sand supply limitations that could lead to unsaturated conditions that thereby alter relationships between u * and H . Similarly to the lidar observations, the work of Rotnicka and Dłużewski (2022) found that H scaled with u . Interestingly, they found a relatively limited response to H on sandy beds for ∼7 m/s < u < 11 m/s.…”

“…It is possible, although as of yet unclear, then whether these two thresholds may reflect distinct (a) initiation (fluid) thresholds and (b) a lower impact threshold necessary to sustain sand grains already in motion, a secondary threshold that is typically about ∼80% of the impact threshold (e.g., Martin & Kok, 2018). The lidar data also suggest that the specific location of measurement may have a big influence on H sa,max which may reflect local grain size controls (e.g., Pähtz & Tholen, 2021; Rotnicka & Dłużewski, 2022), surface moisture effects on the beach (e.g., Nield & Wiggs, 2011), and/or micro‐scale topographic effects (e.g., wrack armoring; Nordstrom et al., 2011).…”

“…However this is at odds with the findings of Dong and Qian (2007) whose wind tunnel observations suggests that H increases with increasing u . Similarly, Rotnicka and Dłużewski (2022) found that H is dependent on both local bed properties and wind speed. Shear dependence or independence on H is hypothesized to provide critical insights on the internal mechanics of the transport field (Martin & Kok, 2017), particularly in terms of the relative roles of splash‐dominated and lifting‐dominated particle entrainment and their influence on the mass flux rate (e.g., Guala et al., 2008; Nishimura & Hunt, 2000; Walter et al., 2014).…”

Skimming Flow and Sand Transport Within and Above Ammophila (Marram) Grass on a Foredune

“…The trap is illustrated in a later figure below. The efficiency of the lower part of the trap was tested in a wind tunnel filled with quartz sand from the Łeba Barrier beach and estimated at 82% regardless of wind speed (Rotnicka & Dłużewski, 2022). Three sand traps were arranged on the bare sand surface: (a) on the middle and upper dune ramps to show the amount of sand deflated from the source area (i.e., dune ramp: ST1 and ST2) and (b) on the uppermost gentle seaward slope (about 1.6 m from the upper edge of steep slope) to estimate the amount of sand supplied to the dune.…”