Understanding the Function of Windbreaks: Basics and Impact on Wind Speed and Flow

1. Windbreak Function(How do they work?) Joe Zeleznik NDSU Extension Forester

2. Windbreak Function - Basics • They slow down the wind • They re-direct the wind • Which modifies the microclimate and environment in protected areas

3. Based on Structure

4. Based on Structure • Density - % solid

7. Based on Structure • Density - % solid • Height – changes over time – height of tallest row

8. Functional Height = Height of the tallest row

10. Based on Structure • Density - % solid • Height – changes over time – height of tallest row • Length –

13. PROTECTED AREA

14. Based on Structure • Density - % solid • Height – changes over time – height of tallest row • Length – • Orientation – perpendicular to prevailing winds

15. WIND

16. From Northerly or northwesterly Direction 12 out of 24 From Southeasterly or Easterly Direction 10 out of 24 From Southwesterly Direction 2 out of 24

17. Based on Structure • Density - % solid • Height – changes over time – height of tallest row • Length – • Orientation – perpendicular to prevailing winds • Continuity

19. Based on Structure • Density - % solid • Height – changes over time – height of tallest row • Length – • Orientation – perpendicular to prevailing winds • Continuity • Species/Number of Rows

21. How does structure affect wind speed and wind flow?

22. Windspeed in the open Fastest Slowest Ground

23. Windspeed in the open Fastest Slowest No turbulence over smooth ground Ground Turbulent flow over a rough surface

24. Windspeed in the open Fastest Turbulent - Random Slowest No turbulence over smooth ground Ground Turbulent flow over a rough surface Eddy – Circular, against main flow

25. Terms to know: H = height of object Upwind Windward Downwind Leeward

26. Pressure eddy Solid barrier 1-2H

27. Suction eddy Turbulent wake zone Resumption of open-field flow Solid barrier 1-3H 3-6H 6-8H

28. Porous barrier Lower effect of pressure eddy

29. Porous barrier Resumption of open-field flow Lower effect of suction eddy Turbulent wake farther downwind

30. Lower branches pruned Resumption of open-field flow Increased snow spreading? Even lower effect of suction eddy Turbulent wake even farther downwind

32. How does structure affect wind speed and wind flow? • Density – determines degree of wind speed reduction (and length of protected zone)

33. Density Upwind Downwind

35. How does structure affect wind speed and wind flow? • Density – determines degree of wind speed reduction (and length of protected zone) • Height – along with density, determines length of protected zone, upwind and downwind

36. WIND HEIGHT Protected Area 2-5 H 10-20 H Protected Area Protected Area

37. How does structure affect wind speed and wind flow? • Density – determines degree of wind speed reduction • Height – with density, determines length of protected zone, upwind and downwind • Length – determines total area of downwind protection

38. LENGTH End effect: Windspeeds increased around end of windbreak by 1.1-1.3 times

39. LENGTH

40. PROTECTED AREA

41. PROTECTED AREA Length:Height - > 10:1

42. How does structure affect wind speed and wind flow? • Density – determines degree of wind speed reduction • Height – with density, determines length of protected zone, upwind and downwind • Length – determines total area of downwind protection • Orientation – place perpendicular to prevailing winds

43. Wind ORIENTATION

44. ? Wind

45. ? PROTECTED AREA Wind

46. Wind PROTECTED AREA ? PROTECTED AREA

47. From Northerly or northwesterly Direction 12 out of 24 From Southeasterly or Easterly Direction 10 out of 24 From Southwesterly Direction 2 out of 24

48. How does structure affect wind speed and wind flow? • Density – determines degree of wind speed reduction • Height – with density, determines length of protected zone, upwind and downwind • Length – determines total area of downwind protection • Orientation – place perpendicular to prevailing winds • Continuity

49. CONTINUITY

50. Brandle and Finch