Abstract
We used a compact boundary layer wind tunnel equipped with a turbulence generator and a piezoelectric blown-sand meter to investigate the effects of the surface coverage of fine gravel on wind-blown sand flux. The vertical profile of wind-blown sand over a flat sand surface showed an exponential distribution at all wind speeds, whereas the profile over gravel surfaces of 20% or greater coverage showed a non-monotonic vertical distribution. At 20% to 30% gravel coverages, a peak of wind-blown sand flux developed between 6 and 10 cm above the ground at all wind speeds because of less energy loss due to grain-bed collisions at that level. To analyze the erosional state of wind-blown sand, we used the Wu–Ling index (λ) of the mass-flux density of sand-bearing wind. Values of λ for all gravel coverages were greater than 1 at all wind speeds, indicating an unsaturated (erosional) state. Moreover, we found that the wind-blown sand flux at 4 cm height accounted for about 20% of the total flux regardless of wind speed and gravel coverage. This finding can simplify future estimations of total near-surface wind-blown sand flux based on field observations because such measurements can be taken at just one height.
Highlights
Desertification and dust storms are severe environmental and socio-economic concerns in many parts of the world, especially in arid and semi-arid regions (e.g., [1])
We measured blown-sand flux in the interval from 2 to 20 cm above the surface, we discuss here only the vertical distribution of relative blown-sand flux within 10 cm of the surface. We chose this interval firstly because it has been recognized that the dominant effect of fine gravel surfaces on blown-sand flux occurs within this layer, and there is marked vertical variation in blown-sand flux outside this height range (e.g., [16,25,26])
The vertical profile of relative blown-sand flux is dependent on gravel coverage, and we the vertical profile of relative blown-sand flux is dependent on gravel coverage, and found that optimal sand-trapping efficiency below 2 cm height occurred at 15% gravel coverage, we found that optimal sand-trapping efficiency below 2 cm height occurred at 15% gravel coverage, the relative blown-sand flux does not control the balance between erosion and deposition by wind-blown the relative blown-sand flux does not control the balance between erosion and deposition by windsand over a fine gravel surface
Summary
Desertification and dust storms are severe environmental and socio-economic concerns in many parts of the world, especially in arid and semi-arid regions (e.g., [1]). Dust storms are common in desertified and otherwise degraded land areas and can have local and regional effects on human and livestock health, air pollution, and soil erosion (e.g., [2,3]). Land surfaces in the Gobi Desert are sensitive to both climate change and human activities, both of which contribute to frequent dust storms that cause progressive desertification [4]. Effective countermeasures for dust transport require an understanding of the vertical profile of wind-blown sand flux. Variations with height of sand flux determine the intensity of sand transport [5], which in turn reflects the saturation state of wind-blown sand and its effect on surface erosion [6]. Results from wind tunnel experiments and field observations have indicated that wind-blown sand transport is a near-surface phenomenon [5]
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