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

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

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Based on Structure

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Density - % solid

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

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Functional Height = Height of the tallest row

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

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PROTECTED AREA

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

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WIND

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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

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

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

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How does structure affect wind speed and wind flow?

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Ground Windspeed in the open Fastest Slowest

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

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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

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

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Solid barrier Pressure eddy 1-2H

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

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Lower effect of pressure eddy Porous barrier

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

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

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

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Density UpwindDownwind

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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

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

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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

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

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LENGTH

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PROTECTED AREA

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Length:Height - > 10:1

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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

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Wind ORIENTATION

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Wind ?

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? PROTECTED AREA

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Wind ? PROTECTED AREA

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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

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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

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CONTINUITY

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Brandle and Finch

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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

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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

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Cross section – no affect, really

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Microclimate modifications

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Windspeed

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Density UpwindDownwind

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Microclimate modifications Windspeed –One consequence – particle fallout – Snowdrift placement

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Microclimate modifications Windspeed Air Temperature Soil Temperature Humidity

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

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Goals for the windbreak

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

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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

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Any Questions?

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