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Wind modification and bed response during saltation of sand in air

  • R. S. Anderson
  • P. K. Haff
Part of the Acta Mechanica Supplementum book series (ACTA MECH.SUPP., volume 1)

Summary

A model of eolian sediment transport has been constructed, a special case of which is that corresponding to sand-sized mineral grains subjected to moderate winds: saltation. The model consists of four compartments corresponding to (1) aerodynamic entrainment, (2) grain trajectories, (3) grain-bed impacts, and (4) momentum extraction from the wind. Each sub-model encapsulates the physics of the process, and is constrained where necessary by experimental data. When combined, the full model allows simulation of eolian saltation from inception by aerodynamic entrainment to steady state.

Many observed characteristics of natural saltation systems are reproduced by the simulations. Steady state mass flux and concentration profiles all display rapid decay with height above the bed, representing the preponderance of short, low-energy trajectories in the saltation population. Yet the role of less abundant, longer, higher energy trajectories is a strong one: at steady state the entire population of saltating grains is controlled by high-energy bed impacts rather than aerodynamic entrainment. Because the nature of the grain splash process is such that high-energy impacts are much more efficient at ejecting other grains from the bed, the response time of the system to changes in wind velocity is determined by the hop time of these long trajectories. Several hop times, or roughly 1–2 seconds, are required.

Varying wind velocity among the simulation runs allows mapping of the relation between steady state mass flux and wind velocity-the mass flux “law”-which may be expressed as a power law of the excess shear velocity. The hysteresis that led Bagnold to define both fluid and impact thresholds for saltation is apparent, reinforcing our conclusion that it is the impacts of saltating grains that supports the large population of saltating grains at steady state.

Keywords

Sediment Transport Mass Flux Shear Velocity Wind Profile Impact Angle 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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References

  1. [1]
    Bagnold, R. A.: The physics of blown sand and desert dunes. London: Methuen 1941.Google Scholar
  2. [2]
    Chepil, W. S.: Dynamics of wind erosion. I. Nature of movement of soil by wind. Soil Sci. 60, 305–320 (1945).CrossRefGoogle Scholar
  3. [3]
    Anderson, R. S.: A theoretical model for aeolian impact ripples. Sedimentology 34, 943–956 (1987).CrossRefGoogle Scholar
  4. [4]
    Anderson, R. S., Haff, P. K.: Simulation of eolian saltation. Science 241, 820–823 (1988).CrossRefGoogle Scholar
  5. [5]
    Anderson, R. S., Hallet, B.: Sediment transport by wind: toward a general model. Geol. Soc. Am. Bull. 97, 523–535 (1986).CrossRefGoogle Scholar
  6. [6]
    White, B. R., Schulz, J.: Magnus effect in saltation. J. Fluid Mech. 81, 497–512 (1979).CrossRefGoogle Scholar
  7. [7]
    Willetts, B. B., Rice, M. A.: Inter-saltation collisions. In: Barndorff-Nielsen, et al. (eds.) Proceedings of the International Workshop on the Physics of Blown Sand, vol. 1. Department of Theoretical Statistics, University of Aarhus, pp. 83–100 (1986).Google Scholar
  8. [8]
    Willetts, B. B., Rice, M. A.: Collisions in eolian saltation. Applications of the mechanics of granular materials. In: Geophysics, Euromech 201 Conference; Interlaken, Switzerland, Oct. 13–18, 1985 (1986).Google Scholar
  9. [9]
    Willetts, B. B., Rice, M. A.: Collisions of quartz grains with a sand bed: influence of incidence angle. Earth Surface Processes and Landforms 14, 719–730 (1989).CrossRefGoogle Scholar
  10. [10]
    Willetts, B. B., Rice, M. A.: Particle dislodgement from a flat bed by wind. Earth Surface Processes and Landforms 13, 717–728 (1988).CrossRefGoogle Scholar
  11. [11]
    Owen, P. R.: Saltation of uniform grains in air. J. Fluid Mech. 20, 225–242 (1964).MATHCrossRefGoogle Scholar
  12. [12]
    Werner, B. T.: A physical model of wind-blown sand transport. Ph. D. dissertation, California Institute of Technology, Pasadena, California USA. p. 441 (1987).Google Scholar
  13. [13]
    Werner, B. T.: A steady state model of windblown sand transport. J. Geol. 98, 1–17 (1990).CrossRefGoogle Scholar
  14. [14]
    Mitha, S., Tran, M. Q., Werner, B. T., Haff, P. K.: The grain-bed impact process in aeolian saltation. Acta Mech. 63, 267–278 (1986).CrossRefGoogle Scholar
  15. [15]
    Rumpel, D. A.: Successive aeolian saltation: studies of idealized collisions. Sedimentology 32, 267–275 (1985).CrossRefGoogle Scholar
  16. [16]
    Werner, B. T., Haff, P. K.: The impact process in eolian saltation: two dimensional studies. Sedimentology 35, 189–196 (1988).CrossRefGoogle Scholar
  17. [17]
    Werner, B. T., Haff, P. K.: Dynamical simulations of granular materials using concurrent processing computers. In: Fox, G. C. (ed.) Proceedings 3rd Conference on Hypercube Concurrent Computer and Applications, Jan. 19–20, 1988, New York: ACM 1988.Google Scholar
  18. [18]
    Ungar, J. E., Haff, P. K.: Steady state saltation in air. Sedimentology 34, 289–299 (1987).CrossRefGoogle Scholar
  19. [19]
    Werner, B. T., Haff, P. K.: A simulation study of the low energy ejecta resulting from single impacts in eolian saltation. In: Arndt, R.E.A., et al. (eds.) Advancements in aerodynamics, fluid mechanics and hydraulics. New York: Am. Soc. Chem. Eng. 1986.Google Scholar
  20. [20]
    Mikkelsen, H., Rasmussen, K. R.: Transport profiles measured with an isokinetic trap (this volume).Google Scholar
  21. [21]
    Gerety, K.: Problems with determination of u* from wind-velocity profiles measured in experiments with saltation. In: Proc. International Workshop on the Physics of Blown Sand, vol. 2, Dept. of Theoretical Statistics, Aarhus University (Denmark), Mem. 8, pp. 271–300 (1986).Google Scholar
  22. [22]
    White, B. R.: Soil transport by wind on Mars. J. Geophys. Res. 84, 4643–4651 (1979).CrossRefGoogle Scholar
  23. [23]
    Greeley, R., Iversen, J.: Wind as a geological process. Cambridge: Cambridge University Press 1985.CrossRefGoogle Scholar
  24. [24]
    Anderson, R. S.: Erosion profiles due to particles entrained by wind: application of an eolian sediment-transport model. Geol. Soc. Am. Bull. 97, 1270–1278 (1986).CrossRefGoogle Scholar
  25. [25]
    Anderson, R. S.: Sediment transport by wind: saltation, suspension, erosion and ripples. Ph. D. dissertation, University of Washington, Seattle (1986).Google Scholar
  26. [26]
    Jensen, J. L., Sørensen, M.: Estimation of some eolian saltation transport parameters: a reanalysis of Williams’ data. Sedimentology 33, 547–555 (1986).CrossRefGoogle Scholar
  27. [27]
    Sørensen, M.: Estimation of some eolian saltation transport parameters from transport profiles. In: Proc. International Workshop on the Physics of Blown Sand, vol. 1. Dept. of Theoretical Statistics, Aarhus University (Denmark), Mem. 8, pp. 141–190 (1986).Google Scholar
  28. [28]
    Smith, J. D., McLean, S. R.: Spatially averaged flow over a wavy surface. J. Geophys. Res. 82, 1735–1746 (1977).CrossRefGoogle Scholar
  29. [29]
    Whiting, P., Dietrich, W. E.: The roughness of alluvial surfaces; an empirical examination of the influence of size homogeneity and natural packing. Eos 70, 1109 (abstract) (1989).Google Scholar
  30. [30]
    Anderson, R. S.: Feedbacks and time scales in eolian saltation. Eos 69, 1195 (abstract) (1988).CrossRefGoogle Scholar
  31. [31]
    Sørensen, M.: The soft bed-a proposal for a self-limiting mechanism for saltation. Program and abstracts of a workshop on dynamics of eolian sediment transport, A.S.U., Tempe, Arizona USA, March 30, 1988, 38–39 (1988).Google Scholar

Copyright information

© Springer-Verlag Wien 1991

Authors and Affiliations

  • R. S. Anderson
    • 1
  • P. K. Haff
    • 2
  1. 1.Earth Sciences BoardUniversity of California Santa CruzSanta CruzUSA
  2. 2.Department of Civil and Environmental EngineeringDuke University, School of EngineeringDurhamUSA

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