January 2008 Barriers – Wind Erosion Prediction System 1

Using Barrierswith the

Wind Erosion Prediction System

WEPS Train-the-Trainer Workshop

January 2008 Barriers – Wind Erosion Prediction System 2

Wind Barriers in WEPS

• Any structure designed to reduce the wind speed on the downwind side of the barrier.– Primarily includes linear plantings of single or

multiple rows of trees, shrubs, or grasses– Could also include snow fences, board walls,

bamboo and willow fences, earthen banks, hand-inserted straw rows, and rock walls

Zone of Protection

January 2008 Barriers – Wind Erosion Prediction System 3

Barrier

• A continuous strip or row of trees, shrubs, or tall grass (annual or perennial) having sufficient height and density to create a sheltered zone downwind

• Barriers generally influence wind erosion for a distance 10 times the height of the barrier

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Barriers &Air Flow Patterns

• A portion of the air flows through a windbreak or herbaceous barrier.

• The remaining air flows around the ends and over the top in a compressed manner. Air Flow Through

WindbreaksVTS_11_1.VOB

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Modifying Air Flow with Barriers

Results include:• Lower wind velocity causing

particulate matter to be deposited• Barrier vegetation physically traps

particulate matter• Barrier vegetation may adsorb some

of the chemicals attached to particulate matter

• Alters the microclimate

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What is H?

H = Effective Height of the Barrrier

H

H

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Why Is Barrier Height Important?

The leeward

distance of wind

protection is

directly

proportional to

the height of the

barrier.

The leeward

distance of wind

protection is

directly

proportional to

the height of the

barrier.

Note: “4H” is in the ‘middle’of the wind protection zone.

January 2008 Barriers – Wind Erosion Prediction System 8

The height determines the distance of the sheltered zone. For example, select the tallest trees suited to the site for large fields and fewest barriers.

Element: Height

Match height to achieve desired protected area

10H to 15H 10H to 15H

H = Height of windbreak

HH

Why Is Barrier Height Important?

January 2008 Barriers – Wind Erosion Prediction System 9

Barrier Height

WEPS defines barrier height as the average height of individual elements.

Assumptions:

Design Height USED was 20 year height.

January 2008 Barriers – Wind Erosion Prediction System 10

Barrier Width

The width of a barrier is defined as the distance from one side of the barrier to the other

January 2008 Barriers – Wind Erosion Prediction System 11

Barrier Porosity

Barrier porosity is the percentage of the open portion of the barrier to the total area of the barrier.

January 2008 Barriers – Wind Erosion Prediction System 12

Barrier Density

Barrier density is the percentage of the solid portion of the barrier to the total area of the barrier.

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What is the difference between Density and Porosity?

• 40 to 50 % porous• OR• 50 to 60 % dense

• 60 to 75 % porous• OR• 25 to 40 % dense

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> 60% Barrier Density (< 40 % Porosity)

A single row windbreak of blue spruce that is about 60 percent dense.

January 2008 Barriers – Wind Erosion Prediction System 15

40 - 60 % Barrier Density (60-40 % Porosity)

This 30 foot high windbreak is about 60 percent dense, although it obviously varies from top to bottom.

January 2008 Barriers – Wind Erosion Prediction System 16

30 - 40 % Barrier Density(70-60 % Porosity)

This single row of young green ash in winter condition is about 40 percent dense.

January 2008 Barriers – Wind Erosion Prediction System 17

80% Porosity

45% Porosity25% Porosity

65% Porosity

January 2008 Barriers – Wind Erosion Prediction System 18

January 2008 Barriers – Wind Erosion Prediction System 20

Determining Barrier Porosity

Effect of pruning lower branches?

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Barrier Data Used for Dropdown List

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Shrub Barriers

Shrub Field Windbreaks in Montana above and

Berry Canes below

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Barrier Data Used for Dropdown List

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Herbaceous Wind Barriers

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Herbaceous Wind Barriers

Corn Rows in

North Dakota

Rye grass in Georgia Rye grass & Carrots in Michigan

January 2008 Barriers – Wind Erosion Prediction System 27

Barrier Data Used for Dropdown List

January 2008 Barriers – Wind Erosion Prediction System 28

Effect of Forest Blocks

Do they function like a narrower windbreak?

January 2008 Barriers – Wind Erosion Prediction System 29

Wind Effects of “Wide” Forest Block

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Wind Effects of “Wide” Forest Block

Wind Direction

January 2008 Barriers – Wind Erosion Prediction System 31

Barrier Data Used for Dropdown List

January 2008 Barriers – Wind Erosion Prediction System 32

Orchards & Vineyards

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Windbreak Orientation

• Orient the buffer perpendicular to the wind

• Allow for variations in wind direction

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Region (L) for Barriers

• WEPS assumes that saltation and creep begin at the edge of the barrier and end at the next barrier or the edge of the field.

• The region becomes the distance between barriers.

• Even down to narrow row vegetated barriers.

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January 2008 Barriers – Wind Erosion Prediction System 37

Barrier Limitations

Protection to the field and plants is limited for until the barrier is established. This may be as little as a year for herbaceous to 10 years for trees and shrubs.

Until the windbreak achieves adequate height and density, supplemental erosion protection may be needed such as conservation tillage. As the windbreak matures, competition with adjoining crops may occur. This can be minimized by choosing low competitive trees/shrubs or root pruning.

January 2008 Barriers – Wind Erosion Prediction System 38

Barrier Limitations

Until the complex field option is made available, the only way to evaluate a field that has a series of barriers across the field, the individual strip needs to be evaluated.

January 2008 Barriers – Wind Erosion Prediction System 39

Questions?Questions?