Analytical model for flux saturation in sediment transport

Pähtz, Thomas; Parteli, Eric J. R.; Kok, Jasper F.; Herrmann, Hans J.

doi:10.1103/physreve.89.052213

Cited by 37 publications

(52 citation statements)

References 70 publications

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“…Due to the effect of the sand-control system and topography on the aeolian sand flow, the ratios of 12 points for 20-60 cm exceeded 20%, but the highest values were primarily located in the 0-20 cm range, indicating that blown sand motion occurred near the sand surface. These results were consistent with those in the literature for mobile sand surfaces (Bagnold, 1941;Chepil, 1963;Williams, 1964;Lammel et al, 2012;Pahtz et al, 2014). Because of the effects of the sand-control system, the ratios at 0-20 cm for the upwind points were larger than those for the leeward points, with a mean upwind value of 0.67 and a mean leeward value of 0.54.…”

Section: 12supporting

confidence: 93%

Blown sand motion within the sand-control system in the southern section of the Taklimakan Desert Highway

Cao

Xing-ri

et al. 2015

J. Arid Land

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Although scientists have performed many studies in the Taklimakan Desert, few of them have reported the blown sand motion along the southern edge of the Taklimakan Desert Highway, which differs significantly from the northern region in terms of aeolian sand geomorphology and formation environment. Based on the field observation data of airflow and aeolian sand transport, continuous monitoring data of erosional and depositional processes between 14 April 2009 and 9 April 2011 and data of surface sand grains from the classical section along the southern edge of the Taklimakan Desert Highway, this paper reported the blown sand motion within the sand-control system of the highway. The main results are as follows: 1) The existing sand-control system is highly effective in preventing and controlling desertification. Wind velocities within the sand-control system were approximately 33%-100% of those for the same height above the mobile sand surface. Aeolian sand fluxes were approximately 0-31.21% of those of the mobile sand surface. Sand grains inside the system, with a mean diameter of 2.89 φ, were finer than those (2.15 φ) outside the system. In addition, wind velocities basically followed a logarithmic law, but the airflow along the classical section was mainly determined by topography and vegetation. 2) There were obvious erosional and depositional phenomena above the surface within the sand-control system, and these phenomena have very consistent patterns for all observation points in the two observed years. The total thicknesses of erosion and deposition ranged from 0.30 to 14.60 cm, with a mean value of 3.67 cm. In contrast, the deposition thicknesses were 1.90-22.10 cm, with a mean value of 7.59 cm, and the erosion thicknesses were 3.51-15.10 cm, with a mean value of 8.75 cm. The results will aid our understanding of blown sand within the sand-control system and provide a strong foundation for optimizing the sand-control system. Hongyan. 2015. Blown sand motion within the sand-control system in the southern section of the Taklimakan Desert Highway. Journal of Arid Land, 7(5): 599-611.

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Section: 12supporting

confidence: 93%

Blown sand motion within the sand-control system in the southern section of the Taklimakan Desert Highway

Cao

Xing-ri

et al. 2015

J. Arid Land

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“…Nevertheless, our observations clearly showed how the asymmetric sand supply and dune collisions are affecting the dune shapes in the Hexi Corridor (as summarized in the conclusions, 1-5, above), and are providing valuable data on sediment size distributions in a field where asymmetric barchan shapes emerge because of local sediment conditions and dune interactions. Recent modeling work has helped to push forward our understanding of sediment transport and dune migration dynamics [64][65][66][67], and the data provided in the present manuscript is valuable to inspire future applications of such theoretical modeling and numerical simulations. It would be interesting to investigate the dune processes in Hexi Corridor by means of numerical modeling, in particular, to verify the conclusions made here on the effect of the sediment source distributions, barchan collisions, and asymmetry in the sediment supply on the dune shape.…”

Section: Discussionmentioning

confidence: 90%

Migration and Morphology of Asymmetric Barchans in the Central Hexi Corridor of Northwest China

Zhang

Dong

et al. 2018

Geosciences

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Crescent-shaped barchan dunes often display an asymmetric shape, with one limb longer than the other. As shown in previous studies, asymmetric bimodal winds constitute one major cause of barchan asymmetry, but the heterogeneous conditions of sand availability or flux, as well as topographic influences, may be also important. Understanding the morphology and dynamics of asymmetric barchans may have an impact in a broad range of areas, particularly as these dunes may serve as a proxy for planetary wind regimes and soil conditions in extraterrestrial environments. However, in addition to the existing theories and numerical models that explain barchan asymmetry, direct measurements of migration rates and morphologic changes of real asymmetric barchans over a time span of several years would be beneficial. Therefore, here we report such measurements, which we have acquired by investigating asymmetric barchans in the Hexi Corridor, northwest of China. We have found that dune interactions and asymmetric influx conditions are the most important causes of barchan asymmetry in this field. Particle size distributions in the Hexi Corridor display strong variations over different parts of the asymmetric barchans, as well as over different dunes, with gravel particles being incorporated from the substrate as the dunes migrate. Our observations have shown that upwind sediment sources are important for dune formation in the Hexi Corridor, and that interdune interactions affect dune shape in different ways, depending on their offset. The asymmetric barchans in the Hexi Corridor are active, with an average migration rate (MR) between 8 and 53 m year −1 , in spite of the different asymmetric shapes. Our data for dune migration rates can be described well by a scaling of MR = A/(W + W0), where W is the barchan cross-wind width, A ≈ 2835 m 2 s −1 , and W0 ≈ 44 m. A similar scaling fits very well the migration rate as a function of dune along-wind width L, (i.e., MR = B/(L + L0), with B ≈ 1722 m 2 s −1 and L0 ≈ 13 m). Linear relations are also found between both dune widths and the average limb and windward side lengths, thus indicating that the morphometric relations that are predicted from models for steady-state, symmetric crescent-shaped dunes can be applied to different transitional morphologies of interacting, asymmetric barchans.

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“…The analytical model for the saturation length of both subaqueous and aeolian particle transport recently proposed by Pähtz et al [, ] is also consistent with these measurements (without fitting), even though the model predicts that L s varies with u ∗ . In this model, the four potentially most important relaxation mechanisms are all accounted for (ejection of bed particles and particle deceleration in particle‐bed collisions, fluid drag acceleration of particles, and relaxation of the fluid speed), and it turns out that neglecting any of them entirely changes the model predictions [ Pähtz et al , ]. This shows that the identity of the most important relaxation mechanisms remains an open problem.…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, we find that

L_{s} \propto V_{s}^{2} / g

, where g is the gravitational constant, when u ∗ >4 u t , where u t is the dynamic threshold of sand transport (i.e., the extrapolated value of u ∗ at which the saturated sand transport rate ( Q s ) vanishes). This finding is consistent with the analytical model by Pähtz et al [, ], supporting the hypothesis that the aforementioned four potentially most important relaxation mechanisms are all similarly relevant.…”

Section: Introductionmentioning

confidence: 99%

Discrete Element Method simulations of the saturation of aeolian sand transport

Pähtz

Omeradžić

Carneiro

et al. 2015

Geophysical Research Letters

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The saturation length of aeolian sand transport (Ls), characterizing the distance needed by wind‐blown sand to adapt to changes in the wind shear, is essential for accurate modeling of the morphodynamics of Earth's sandy landscapes and for explaining the formation and shape of sand dunes. In the last decade, it has become a widely accepted hypothesis that Ls is proportional to the characteristic distance needed by transported particles to reach the wind speed (the “drag length”). Here we challenge this hypothesis. From extensive numerical Discrete Element Method simulations, we find that, for medium and strong winds, Ls∝Vs2/g, where Vs is the saturated value of the average speed of sand particles traveling above the surface and g is the gravitational constant. We show that this proportionality is consistent with a recent analytical model, in which the drag length is just one of four similarly important length scales relevant for sand transport saturation.

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Analytical model for flux saturation in sediment transport

Cited by 37 publications

References 70 publications

Blown sand motion within the sand-control system in the southern section of the Taklimakan Desert Highway

Blown sand motion within the sand-control system in the southern section of the Taklimakan Desert Highway

Migration and Morphology of Asymmetric Barchans in the Central Hexi Corridor of Northwest China

Discrete Element Method simulations of the saturation of aeolian sand transport

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