windbreak function (how do they work?) joe zeleznik ndsu extension forester
TRANSCRIPT
Windbreak Function(How do they work?)
Joe ZeleznikNDSU Extension Forester
Windbreak Function - Basics
• They slow down the wind
• They re-direct the wind
• Which modifies the microclimate and environment in protected areas
Based on Structure
Based on Structure
• Density - % solid
Based on Structure
• Density - % solid
• Height – changes over time
– height of tallest row
Functional Height = Height of the tallest row
Based on Structure
• Density - % solid
• Height – changes over time
– height of tallest row
• Length –
PROTECTED AREA
Based on Structure
• Density - % solid
• Height – changes over time
– height of tallest row
• Length –
• Orientation – perpendicular to prevailing winds
WIND
Predominant Wind DirectionsLocation
Direction % Time Direction % Time Direction % Time Direction % TimeNNW 17 NNW 17 SSE 17 SSE 18SSE 17 SSE 13 N 14 NNW 10NW 11 NW 10 SE 14 NW 16E 10 SE 10 NW 12 SE 14
NW 18 NW 16 NW 14 NW 17SW 13 SE 12 SE 12 SW 13
Fargo
Bismarck
Minot
Time of yearJanuary April July October
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
Based on Structure
• Density - % solid
• Height – changes over time
– height of tallest row
• Length –
• Orientation – perpendicular to prevailing winds
• Continuity
Based on Structure
• Density - % solid• Height – changes over time – height of tallest row• Length – • Orientation – perpendicular to prevailing
winds• Continuity• Species/Number of Rows
How does structure affect wind speed and wind flow?
Ground
Windspeed in the open
Fastest
Slowest
Ground
Windspeed in the open
Fastest
Slowest
No turbulence over smooth ground
Turbulent flow over a rough surface
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
Terms to know:
Upwind
Windward
Downwind
Leeward
H = height of object
Solid barrier
Pressure eddy
1-2H
Solid barrier
Suction eddy
1-3H 3-6H
Turbulent wake zone
6-8H
Resumption of open-field flow
Lower effect of pressure eddy
Porous barrier
Lower effect of suction eddy
Turbulent wake farther downwind
Resumption of open-field flow
Porous barrier
Even lower effect of suction eddy
Turbulent wake even farther downwind
Resumption of open-field flow
Lower branches pruned
Increased snow spreading?
How does structure affect wind speed and wind flow?
• Density – determines degree of wind speed reduction (and length of protected zone)
Density
Upwind Downwind
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
WIND
Protected Area
Protected Area
Protected Area
HEIGHT
2-5 H 10-20 H
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
LENGTH
End effect: Windspeeds increased around end of windbreak by 1.1-1.3 times
LENGTH
PROTECTED AREA
PROTECTED AREA
Length:Height - > 10:1
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
Wind
ORIENTATION
Wind
?
Wind
? PROTECTED
AREA
Wind
?
PROTECTED AREA
PROTECTED AREA
Predominant Wind DirectionsLocation
Direction % Time Direction % Time Direction % Time Direction % TimeNNW 17 NNW 17 SSE 17 SSE 18SSE 17 SSE 13 N 14 NNW 10NW 11 NW 10 SE 14 NW 16E 10 SE 10 NW 12 SE 14
NW 18 NW 16 NW 14 NW 17SW 13 SE 12 SE 12 SW 13
Fargo
Bismarck
Minot
Time of yearJanuary April July October
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
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
CONTINUITY
Brandle and Finch
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
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
Cross section – no affect, really
Microclimate modifications
Microclimate modifications
• Windspeed
Density
Upwind Downwind
Microclimate modifications
• Windspeed– One consequence – particle fallout Snowdrift placement
Microclimate modifications
• Windspeed
• Air Temperature
• Soil Temperature
• Humidity
Microclimate modifications
• Windspeed
• Air Temperature
• Soil Temperature
• Humidity
• Heat loss (animals and buildings)
Goals for the windbreak
Goals for the windbreak
• Design considerations (density, placement) are based on goals:
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
Any Questions?