E Climatic conditions

Snow and ice often hamper farm operations and cause critical runoff conditions during periods of melt. Where appropriate, the depth and location of snowdrift as well as ice and other winter conditions should be considered when siting an AWMS. Accumulation of snow on a waste storage pond or lagoon may not be desirable in areas where precipitation is abundant, especially as a waste storage pond nears capacity late in winter. Conversely, in more arid regions or areas where most of the precipitation is received as snow, accumulation within the waste storage facility may be desirable. In both cases, vegetation and fences are effective in trapping snow.

The distance to which a fence or vegetative windbreak will affect snow accumulation is dependent on its height and porosity and on the windspeed. A solid fence (0% porosity) causes most snow deposition to occur on the upwind (windward) side. However, its effective distance downwind (leeward) is so limited it is not recommended for use with an AWMS. Fences

Figure 8-22 An aboveground storage tank is inconspicuous on this highly scenic landscape

Figure 8-22 An aboveground storage tank is inconspicuous on this highly scenic landscape

that have 15 to 25 percent porosity trap snow on the downwind side in an area that is as long as the fence and as wide as four or five times the fence's height. The standard snow fence is 4 feet high and 50 percent porous. Deposition occurs from the base of the fence to about 40 feet downwind. Figure 8-23 illustrates how fence porosity affects snow deposition patterns. As shown, a 50 percent porous barrier captures about four times as much snow as a 15 percent porous barrier. The same conditions are true for windblown soil in the more arid regions of the country.

Because of the additional height, vegetative windbreaks influence snow and windblown soil deposition over a greater distance than fences. Depending upon location, they may provide additional benefits including odor reduction, screening, temperature control, and wildlife habitat. Available planting space and the amount of snow or soil deposition anticipated will influence the location, width, and alignment of windbreaks.

When managing snow or soil deposition, the use of fences and vegetation should be combined whenever feasible. The fence will provide immediate results, while vegetation, which may require several years growing time, often provides additional multiple benefits. A second fence may be required near windbreaks to prevent livestock from damaging the vegetation. Figure 8-24 illustrates how a fence and multiple rows of vegetation with 50 percent porosity influence deposition.

Agricultural waste facilities that have the back wall protected from the wind, such as an open-front dry manure storage building, tend to have some snow accumulation just inside the front door. To prevent this, a 6- to 8-inch slot can be cut in the rear wall near the eaves to provide some wind penetration.

Ice buildup can be reduced by considering shade patterns of buildings and vegetation. Because deciduous trees shade only in summer and allow heat-generating sunlight in the winter, they are more effective than evergreens in regulating a microclimate affecting ice and snow accumulations. A mixture of deciduous trees and evergreen understory can often provide a desired screen during winter while serving the need to minimize buildup.

Fences can also be located to deposit snow or windblown soil away from building openings (fig. 8-25).

Figure S-2S Fence porosity affects snow deposition

Wind

Solid fence

15% Porous

Normal deposition

Normal deposition

Waste storage pond

Solid fence

15% Porous

Waste storage pond

Porous fence

Deposition area—snow or soil

Waste storage pond

Porous fence

Deposition area—snow or soil

Waste storage pond

Figure 8-24 The combination of fence and windbreak plantings greatly enhances the pattern of snow and soil deposition

Prevailing winds

Windbreak planting

Livestock exclusion as needed

Porous fence

Porous fence

Waste storage pond

Major deposition zone

10x tree height - Deposition area-

Zone free of drifted snow or soil

Figure 8-25 Fences affect snow and soil deposition around buildings

Storage bunker

Wind

Porous fence

Snow or soil I

Storage bunker

Snow or soil I

Wind

Storage bunker

Porous fence

Porous fence

Storage bunker

Porous fence

Shed

Before

After

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