With the memory of last year's 20-ft snow banks still in mind, many rural residents of the Dakotas, Minnesota, and Wisconsin have requested information on how tree windbreaks and snow fences can better protect their farmsteads and building sites from snow. Even though winter 1997-98 has produced little snow so far, the following suggestions can help farmers and other rural residents avoid some of the problems created by drifting snow.
When placing a snow fence or tree windbreak or shelterbelt, consider that the protected downwind area will generally be 10 to 15 times the height of the fence or trees. For example, an 80% solid, 12-ft high windbreak fence will protect an area 120 to 180 ft downwind. Also, most of the snow will drop within roughly the first 25% of the protected area. For the example of the 12-ft high fence, most of the snow would pile up within 30 to 45 ft of the fence. It is very important to leave space for snow to accumulate when locating machine sheds or livestock buildings downwind from a windbreak. If the buildings are too close to the windbreak, they will be within the snow drop area, and if they are too far away, they will be outside of the wind "protection" zone.
Another important piece of information is the prevailing wind direction for your farm or building site. It is a good idea to obtain a "wind rose" for your location. Wind roses indicate the percentage of time that the wind blows from different directions during different times of the year. Knowledge of wind direction will help you determine the best location for windbreaks. It will also help you estimate cost/benefit information for establishing different types of windbreaks (like a fence vs. a tree shelterbelt) to provide protection from storms coming from an unusual direction.
Finally, providing some wind protection with a fence is best accomplished by constructing a fence which has an 80% solid surface area. For example, if 1x10 boards are used, you would space them 2.5 in. apart and if 1x8s are used, the spacing would be 2 in. Corrugated metal roofing or siding can be used to construct windbreak fences, but the sheets should be ripped in half, lengthwise, so the maximum width is 14 to 15 in. With a sheet width of 14 to 15 in., the spacing between sheets should be approximately 4 to 5 in.
This page is part of the Biosystems and Agricultural Engineering Department web at http://www.bae.umn.edu/