Using Barriers with the Wind Erosion Prediction System WEPS Train-the-Trainer Workshop

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

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

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 Windbreaks VTS_11_1.VOB

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

What is H? H = Effective Height of the Barrrier H H Height - Buffer height (H) is one of the most important factors in determining the downwind distance of buffer protection. This value varies from buffer to buffer depending on the plant materials used and the age of the buffer. As the buffer matures the H value increases. In multiple-row windbreaks, the height of the tallest tree-row determines the value of H. The height of a barrier is the average height of individual elements (e.g. trees) in the barrier (“a” in Fig. 3.16 for single row barriers). The units of measure for barrier height are displayed on the input screen in feet or meters. For multiple row barriers, use the height of the tallest barrier row (“b” in Fig. 3.16). H = Effective Height of the Barrrier

Why Is Barrier Height Important? The leeward distance of wind protection is directly proportional to the height of the barrier. Height - Windbreak height (referred to as ‘H’) is the most important factor determining the downwind area of protection. The windbreak ‘H’ is the height of the tallest row of trees in the windbreak. The windbreak will reduce wind speed for 2 to 5 times the height of the windbreak (2H to 5H) on the upwind side and up to 30H on the downwind side of the barrier. The area protected is a direct proportion to the height, i.e. the 20 foot windbreak in the diagram will have a 40% reduction at 4H or 80 feet downwind but a 60 foot windbreak reduce the wind velocity by 40% for a distance of 240 feet or 4H. Note: “4H” is in the ‘middle’ of the wind protection zone.

Why Is Barrier Height Important? Element: Height Match height to achieve desired protected area H = Height of windbreak 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. H 10H to 15H 10H to 15H

Barrier Height WEPS defines barrier height as the average height of individual elements. Assumptions: Design Height USED was 20 year height. The height of a barrier is the average height of individual elements (e.g., trees) in the barrier (“a” in Fig. 3.15 for single-row barriers). The units of measure for barrier height are displayed on the input screen in feet or meters. For multiple-row barriers, use the height of the tallest barrier row (“b” in Fig. 3.15). For the Tree and Shrub barriers, the heights used are based on the 20-year heights which is the standard height used for designing windbreaks. Since the model does not grow the barriers, it needs to be recognized that erosion rates will gradually decrease during the growth of the barrier. Because of this, alternative treatment options will need to be used during this growth period such as annual barriers, herbaceous barriers and/or changes in crop residue management.

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

Barrier Porosity Density - is the ratio of the solid portion of the barrier to the total area of the barrier. Wind flows through the open portions of a windbreak, thus the more solid the windbreak, the less wind passes through. By adjusting windbreak density different wind flow patterns and areas of protection are established Barrier porosity is the percentage of the open portion of the barrier to the total area of the barrier.

Barrier Density Density - is the ratio of the solid portion of the barrier to the total area of the barrier. Wind flows through the open portions of a windbreak, thus the more solid the windbreak, the less wind passes through. By adjusting windbreak density different wind flow patterns and areas of protection are established Barrier density is the percentage of the solid portion of the barrier to the total area of the barrier.

What is the difference between Density and Porosity? Density - is the ratio of the solid portion of the barrier to the total area of the barrier. Wind flows through the open portions of a windbreak, thus the more solid the windbreak, the less wind passes through. By adjusting windbreak density different wind flow patterns and areas of protection are established 40 to 50 % porous OR 50 to 60 % dense 60 to 75 % porous OR 25 to 40 % dense

> 60% Barrier Density (< 40 % Porosity) Pictured above is a single row windbreak of blue spruce (Picea pungens) that is about 60 percent dense and 20 feet tall with six feet within row spacing. • At least two rows of conifer trees are necessary to achieve density greater than 60 percent. For example, spruces, junipers, firs and arborvitae (Picea, Juniperus, Abies or Thuja spp.) are recommended, but pines (Pinus spp.) tend not to be as dense and have a tendency to open up with age. • Many shrubs, even without leaves, can provide enough density for this purpose, but only at lower heights. For example Siberian pea shrub (Caragana spp.) in the northern plains and “Streamco” willow (Salix purpurea) in the northeast have been effectively used for living snowfences to protect roads. • Species need to be durable to withstand breakage due to the weight of accumulated snow. • Once the basic windbreak design addresses the minimum density, additional species and rows can be added to achieve secondary goals, such as adding value for wildlife or aesthetics. A single row windbreak of blue spruce that is about 60 percent dense.

40 - 60 % Barrier Density (60-40 % Porosity) This windbreak is composed of two rows of Scotch pine (Pinus sylvestris) planted at six foot spacing and about ten feet between rows. This 30 foot high windbreak is about 60 percent dense, although it obviously varies from top to bottom. • A single row of deciduous trees such as oaks, ashes, hackberry, poplars, etc. (Quercus, Fraxinus, Celtis, Populus spp.) planted about 12 feet apart will be about 60 percent dense and provide adequate crop protection during the growing season when the trees are in leaf. • A single row of dense conifers, like spruces and others noted above, planted at close spacing (less than 10 feet) will be about 60 percent dense, while pine trees average about 50 percent dense. • Two or more rows of trees increases density and reduce the possibility of gaps. • When a shrub row is added to a tree row the density at lower heights will increase to greater than 60 percent. • Soil erosion control and snow distribution are nearly incompatible purposes for a single windbreak. A single row of pine with wide within row spacing, 12 feet or greater, is a compromise. Another alternative is to create a system that uses 40 percent dense windbreaks with other soil conservation practices including herbaceous wind barriers and various forms of residue and tillage management. This 30 foot high windbreak is about 60 percent dense, although it obviously varies from top to bottom.

30 - 40 % Barrier Density (70-60 % Porosity) This single row of young green ash (Fraxinus pennsylvanica) in winter condition is about 40 percent dense and is ideal for distributing snow across a field. Potential risks of emerald ash borer suggest that species other than green ash should be used in windbreak plantings, particularly when gaps must be avoided. • A single row of deciduous trees such as oaks, ashes, hackberry, poplars, etc. (Quercus, Fraxinus, Celtis, Populus spp.) planted between 14 and 18 feet apart is about 40 percent dense without leaves. • Even though snow distribution is a primary purpose, the distance between the windbreaks should be based on the crop protection or soil protection criteria, whichever is relevant for the landowner objectives and also accommodates equipment width. • A single row of shrubs with no leaves planted at about four foot spacing is typically greater than 40 percent dense. Plantings of this density can still create drifts that are problematic in areas with high snow fall and wind. In southern areas with minimal snow fall the spring thaw occurs early enough to allow the soil to dry allowing timely field operations. This single row of young green ash in winter condition is about 40 percent dense.

80% Porosity 65% Porosity 25% Porosity 45% Porosity

Density - The density level is manipulated by the choice of plant materials (e.g. deciduous trees versus conifers) and the way the plants are arranged in the windbreak. By combining low growing shrubs with medium and tall deciduous trees, dense plant material is provided at three levels (low, middle and upper) of the windbreak during the growing season. However, during the winter, the density would decrease due to the loss of foliage. Consequently, a conifer component would be desirable for year-round protection.

Determining Barrier Porosity Effect of pruning lower branches?

Determining Barrier Porosity Effect of pruning lower branches?

Barrier Data Used for Dropdown List

Shrub Field Windbreaks in Montana above and Berry Canes below Shrub Barriers Shrub Field Windbreaks in Montana above and Berry Canes below

Barrier Data Used for Dropdown List

Herbaceous Wind Barriers

Herbaceous Wind Barriers Rye grass in Georgia Rye grass & Carrots in Michigan Corn Rows in North Dakota

Barrier Data Used for Dropdown List The Herbaceous barriers were divided between perennial and annual. The perennial barriers include species such as switchgrass, tall wheatgrass, elephant grass, etc. The annual barriers were divided into three height categories: short, medium and tall. The short annual barriers could include small grains e.g, wheat, barley, or rye. These small grains provide protection to wind sensitive crops in the early growth stages and are usually sprayed with herbicide. The medium annual barriers also include the small grains as well as flax that are allowed to grow nearly to maturity before being sprayed. The tall annual barriers may include corn, sunflowers, or sorghum reaching heights of 4 to 5 feet. The default porosities assigned to these annual barriers are based on the assumption that the planting rate/acre is the same whether it is one row or two rows or three rows. The porosity of a single row could be altered by increasing the number of plants per acre.

Effect of Forest Blocks Do they function like a narrower windbreak?

Wind Effects of “Wide” Forest Block

Wind Effects of “Wide” Forest Block Wind Direction

Barrier Data Used for Dropdown List The orchard default values include two age categories: one year old and mature height. They are also divided into three size classes: dwarf, semi-dwarf, and standard. The height of some fruit trees can be controlled by the type of root stock such as an apple tree that is dwarf may have a 7 to 8 foot mature size while a standard tree may reach 16 to 18 feet. It was assumed that the dwarf size trees were spaced about 12 feet apart, the semi-dwarf about 20 feet and the standard up to 30 feet for the larger nut trees such as walnut and pecan. The “Forest Edge” example is trying to account for large patches of forest on the field edge. These forest patches are assumed to be “wide” i.e. several hundred feet wide. These patches do not function the same as a windbreak in modifying wind flow. The tendency is for the wind reduction profile adjacent to these wide patches to be reduced in length acting more similarly to the wind profile of a more porous barrier where the wind will return to open field velocity more quickly than a narrower windbreak.

Orchards & Vineyards

Windbreak Orientation Orientation - Windbreaks are most effective when oriented at right angles to prevailing or troublesome winds. The best orientation for each windbreak depends on the objectives for the windbreak. A key point to remember is that although the troublesome wind may occur primarily from one direction, it rarely blows exclusively from that direction. As the wind changes direction and is no longer blowing directly against the windbreak, the protected area decreases. Orient the buffer perpendicular to the wind Allow for variations in wind direction

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.

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. The following are some of the assumptions used in building the default property values for the barriers. For the Tree and Shrub barriers, the heights used are based on the 20-year heights which is the standard height used for designing windbreaks. Since the model does not grow the barriers, it needs to be recognized that erosion rates will gradually decrease during the growth of the barrier. Because of this, alternative treatment options will need to be used during this growth period such as annual barriers, herbaceous barriers and/or changes in crop residue management.

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. The following are some of the assumptions used in building the default property values for the barriers. For the Tree and Shrub barriers, the heights used are based on the 20-year heights which is the standard height used for designing windbreaks. Since the model does not grow the barriers, it needs to be recognized that erosion rates will gradually decrease during the growth of the barrier. Because of this, alternative treatment options will need to be used during this growth period such as annual barriers, herbaceous barriers and/or changes in crop residue management.

Questions?