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. 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. Ground Windspeed in the open Fastest Slowest

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

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

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

26. Solid barrier Pressure eddy 1-2H

27. Solid barrier Suction eddy 1-3H3-6H Turbulent wake zone 6-8H Resumption of open-field flow

28. Lower effect of pressure eddy Porous barrier

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

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

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

33. Density UpwindDownwind

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 Protected Area HEIGHT 2-5 H 10-20 H

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. 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

46. Wind ? 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

51. 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 Species/Number of Rows – affect density, rate of height growth

52. 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 Species/Number of Rows – affect density, rate of height growth Cross section

53. Cross section – no affect, really

54. Microclimate modifications

55. Windspeed

56. Density UpwindDownwind

57. Microclimate modifications Windspeed –One consequence – particle fallout –  Snowdrift placement

58. Microclimate modifications Windspeed Air Temperature Soil Temperature Humidity

60. Microclimate modifications Windspeed Air Temperature Soil Temperature Humidity Heat loss (animals and buildings)

61. Goals for the windbreak

62. Design considerations (density, placement) are based on goals:

63. Goals for the windbreak Design considerations (density, placement) are based on goals: –Crop protection –Reduced soil erosion –Increased snow capture in field –Farmstead protection –Living snow fence –Sound barrier –Wildlife food/cover

65. Any Questions?