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Journal of Arid Land  2021, Vol. 13 Issue (6): 599-611    DOI: 10.1007/s40333-021-0104-3
Research article     
Large scale sand saltation over hard surface: a controlled experiment in still air
LIU Benli1,2,*(), WANG Zhaoyun1,3, NIU Baicheng4, QU Jianjun1,2
1Key Laboratory of Desert and Desertification, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China
2Research Station of Gobi Desert Ecology and Environment in Dunhuang of Gansu Province, Lanzhou 730000, China
3University of Chinese Academy of Sciences, Beijing 100049, China
4Qinghai Normal University, Xining 810004, China
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Saltation is the major particle movement type in wind erosion process. Saltating sand grains can rebound up to tens of times larger in length and height over hard surface (such as gravel surface) than over loose sand surface. Gravels usually have different faces, causing distinct response of the impacting grains, but the effects of the grain and gravel-surface contact angle on grain rebound are not yet well quantified. We performed full-range controlled experiments of grain saltation using different contact angles, grain sizes and impact speeds in still air, to show that contact angle increases the height of representative saltation path but decreases particle travel length. The results were compared with outputs from the COMprehensive numerical model of SALTation (COMSALT). Large saltation height of 4.8 m and length of 9.0 m were recorded. The maximum and representative saltation height over the gravel surface were found to be about 4.9 times and 12.8 times those over the loose sandy surface, respectively. The maximum saltation length may be reduced by 58% and the representative saltation height may be increased by 77% as contact angle increases from 20° to 40°. We further showed that the collision inertia contributes 60% of the saltation length, and wind contributes to the other 40%. These quantitative findings have important implications for modeling saltation trajectory over gravel surface.

Key wordssand saltation      trajectory      gravel surface      contact angle      full-scale experiment     
Received: 14 March 2021      Published: 10 June 2021
Corresponding Authors: LIU Benli     E-mail:
About author: LIU Benli (E-mail:
Cite this article:

LIU Benli, WANG Zhaoyun, NIU Baicheng, QU Jianjun. Large scale sand saltation over hard surface: a controlled experiment in still air. Journal of Arid Land, 2021, 13(6): 599-611.

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Fig. 1 Evidence of large scale saltation over gravel surface. (a), serious sand abrasion of a wood pole on windward side from about 0.1 m to more than 1.5 m in a Gobi area of Xinjiang, but the bottom part below 0.1 m is less damaged; (b), abrasion of a concrete bridge pier (indicated by the ellipse) shows the strongest abrasion at about 0.8 m high; (c), sand deposited behind a 3.3 m high wall as wind breaker at a section of the Lanzhou-Xinjiang high-speed railway; and (d), grain-size distribution of five samples from the site shown in (c). At the three sites of (a)-(c), wind is almost unidirectional, with sand blowing toward the abrasion side in (a) and (b) but another side of the wall in (c).
Fig. 2 Equipments used in the experiments. (a), a sketch of the test equipment with the power section, control panel, contact slate with its contact angle (θ), a horizontal nozzle to simulate an impact angle (β), the liftoff angle (α) of rebound particles, and the horizontal and vertical sand-catch bins (the inset shows the relationships ofθ, α and βin details); (b), horizontal bins to collect sands on the floor; and (c), removing of vertical bins; (d), tested relationship between used pressure and air speed, in which v is impact speed and p is air pressure; (e), distribution of counted gravel inclination angles.
Fig. 3 Concentration contour maps of the saltation space for fine sand. Each column shows different impact speed (v) with the same contact angle θ, and each row shows the effect of θ under the same impact speed. Large light gray areas in each penal indicate low possibility to encounter particles, and most of the particles concentrate at a small range (the representative trajectory). Log scale is used to show the changes of region with low concentrations. Some isolated light patches exist, because zero concentration was measured below or before the patches.
Fig. 4 Concentration contour maps of the saltation space for medium sand
Fig. 5 Concentration contour maps of the saltation space for coarse sand
Fig. 6 Profiles of maximum concentration (Hc) and maximum position (Hm). Each column shows different θ, and each row shows different particle sizes. Hm is apparently higher than Hc, meaning that particles may rise to a much higher location.
Fig. 7 Characteristic trajectory values for three grain sizes (one column for each size) under different impact speeds and contact angles. Lm, maximum saltation length.
Particle size θ y=a×v+b
Lm Hc Hm
a b R2 P a b R2 P a b R2 P
Fine 20° 13.40 -74.00 0.92 0.04 1.87 -13.20 0.93 0.03 4.84 1.10 0.85 0.07
30° 9.90 -24.00 0.77 0.12 3.14 -34.10 0.83 0.09 6.05 -24.75 0.69 0.17
40° 8.10 -36.00 0.88 0.06 1.38 24.75 0.95 0.02 6.88 -49.50 0.87 0.07
Medium 20° 17.90 -124.00 0.98 0.01 2.26 -17.05 0.99 0.00 10.34 -100.65 0.98 0.01
30° 11.80 -3.00 0.84 0.08 2.37 -1.65 0.98 0.01 6.99 7.15 0.91 0.04
40° 13.40 -134.00 0.97 0.01 4.24 -34.10 1.00 0.00 9.19 -50.60 0.98 0.01
Coarse 20° 16.50 85.00 0.99 0.00 2.08 15.50 0.94 0.03 8.75 -32.45 0.97 0.01
30° 14.40 111.00 0.96 0.02 2.20 57.75 0.56 0.25 9.19 9.90 1.00 0.00
40° 12.90 -14.00 0.99 0.00 3.57 35.75 0.83 0.09 10.01 -28.60 1.00 0.00
Table 1 Linear regression coefficients for Lm, Hc and Hm with impact speed v at different particle size and contact angle
Fig. 8 Relationship between saltation length/height (Lm/Hc and Lm/Hm) and liftoff angle (α) of the test results in still air. Unfilled symbols are those adjusted by 1.7 times to match blown sand results in wind tunnel experiments by Ling and Wu (1980).
Fig. 9 Comparison between the test and COMSALT-simulated Lm (a), Hm (b) and Hc (c) in still air for three particle size groups. The test is found to be conservative in reflecting saltation length (a), but clearly shows that current saltation model for flat surface conditions underestimate the saltation height over hard contact surface like the Gobi. The differences can be 4.9 times forHm and 12.8 times for Hc.
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