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

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

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 1-3H3-6H 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 UpwindDownwind

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 HEIGHT 2-5 H 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 times

LENGTH

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 ?

? PROTECTED AREA

Wind ? PROTECTED AREA

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

Windspeed

Density UpwindDownwind

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

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?