Wim Cornelis, Greet Oltenfreiter, Donald Gabriels & Roger Hartmann

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

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

3. Saltation Introduction – some theory Rainless conditions

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

5. Splash Introduction – some theory Windfree conditions detachment

6. Splash Introduction – some theory Windfree conditions or Qr e.g. Sharma & Gupta (1989)

7. Rainsplash-saltation Introduction – some theory Wind-driven rain conditions

8. Rainsplash-saltation Introduction – some theory Wind-driven rain conditions

9. Introduction – some theory Total sediment transport rate

10. Introduction – some theory Objectives: • Determine sediment mass flux qx and qz(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 Qwr (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 KEor M) Shear velocity u* 5 vane probes Kinetic energy KEz or Momentum Mz splash cups Mass flux qx 23 troughs Mass flux qz 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. v from nomograph of Laws (1941) S (rainsplash from cup) Materials and methods Kinetic energy or Momentum

16. Materials and methods Kinetic energy or Momentum

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

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

19. Materials and methods

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

21. Results – wind-driven rain Vertical deposition flux qx (g m-2 s-1) R2 > 0.99

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

23. Results – wind-driven rain Horizontal flux qz (g m-2 s-1) R2 > 0.98

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

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

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

27. Results – wind-driven rain Transport rate Q (g m-1 s-1) R2 = 0.96 R2 = 0.93 R2 = 0.92

28. Results – wind-driven rain u* and KEzor Mz

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

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

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

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

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

34. Conclusions • 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.

35. Conclusions • Sediment transport rate Q relates well to normal component of KE or M (R2 = 0.93). • Observed variation is better explained if u* is considered as well (R2 = 0.96). • Qwr > Qw at low shear velocitiesQw >> Qwr at high shear velocities