1. Wim Cornelis, Greet Oltenfreiter, Donald Gabriels & Roger Hartmann WEPP-WEPS workshop, Ghent-Wageningen, 2003 Splash-saltation of sand due to wind-driven rain

2. Outline of presentation Introduction: some theory Materials and methods Results Conclusions

3. Introduction – some theory Rainless conditionsSaltation

4. e.g.Owen (1964) Lettau & Lettau (1977) Rainless conditionsSaltation Introduction – some theory

5. Windfree conditionsSplash detachment Introduction – some theory

6. Windfree conditionsSplash e.g.Sharma & Gupta (1989) or Q r Introduction – some theory

7. Wind-driven rain conditionsRainsplash-saltation Introduction – some theory

8. Wind-driven rain conditionsRainsplash-saltation Introduction – some theory

9. Total sediment transport rate Introduction – some theory

10. Objectives: Determine sediment mass flux q x and q z (kg m -2 s -1) and express them as function of x and z resp. under wind-driven rain (and rainless wind) conditions Determine sediment transport rate Q wr (kg m -1 s -1 ) and relate them to rain and wind erosivity (KE or M and u * )

11. 1. Vertical deposition flux in kg m -2 s -1 Horizontal mass flux in kg m -2 s -1 ICE wind-tunnel experiments (dune sand, under different u * and KE or M) Kinetic energy KE z or Momentum M z splash cups Shear velocity u * 5 vane probes Mass flux q x 23 troughs Mass flux q z 4 W&C bottles Materials and methods

12. Shear velocity u * wind-velocity profiles 5 vane probes Materials and methods Shear velocity

13. Materials and methods Shear velocity

14. Materials and methods Shear velocity

15. Materials and methods Kinetic energy or Momentum v from nomograph of Laws (1941) S (rainsplash from cup)

16. Materials and methods Kinetic energy or Momentum

17. Materials and methods SaltiphoneSensit “KE of rain field sensor” Did not work properly under given circumstances

18. 2. Mass transport rate in kg m -1 s -1 Calibration Contribution of E (KE z or M z ) u * Validation Materials and methods

20. Results – wind-driven rain Vertical deposition flux q x (g m -2 s -1 )

21. Results – wind-driven rain R 2 > 0.99

22. Horizontal flux q z (g m -2 s -1 ) Results – wind-driven rain

23. Horizontal flux q z (g m -2 s -1 ) Results – wind-driven rain R 2 > 0.98

24. Calibration Contribution of E (KE z or M z ) u * Validation Transport rate Q (g m -1 s -1 ) Results – wind-driven rain

25. Transport rate Q (g m -1 s -1 ) Results – wind-driven rain

26. Transport rate Q (g m -1 s -1 ) Results – wind-driven rain

27. Transport rate Q (g m -1 s -1 ) R 2 = 0.96 R 2 = 0.93 R 2 = 0.92 Results – wind-driven rain

28. u * and KE z or M z Results – wind-driven rain

29. Results – rainless wind (control) Vertical deposition flux q x (g m -2 s -1 )

30. Horizontal flux q z (g m -2 s -1 ) Results – rainless wind (control)

31. Transport rate Q (g m -1 s -1 ) Results – rainless wind (control)

32. Transport rate Q (g m -1 s -1 ) Results – rainless wind (control)

33. Results – wind-driven rain vs. rainless wind

34. Vertical deposition flux of sand was described with double exponential equation, q = f(x). Horizontal flux of sand was described with single exponential equation, q = f(z). Same expressions (and same equipment) can be used for wind-driven rain and rainless wind conditions. But model coefficients are different. Conclusions

35. Sediment transport rate Q relates well to normal component of KE or M (R 2 = 0.93). Observed variation is better explained if u * is considered as well (R 2 = 0.96). Q wr > Q w at low shear velocities Q w >> Q wr at high shear velocities Conclusions