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United States Department of Agriculture

Agricultural Research Service

Title: Wind Velocity Patterns As Modified by Plastic Pipe Windbarriers

Authors
item Bilbro Jr, James
item Stout, John

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 30, 1998
Publication Date: N/A

Interpretive Summary: When soil particles are moved along the ground or carried into the air by the wind, it is called wind erosion. Wind erosion causes many problems, including damaging plants, polluting the air, and adversely affecting equipment and people's health. Wind erosion damage can be lessened or prevented by several methods. One method is to keep most of the soil covered with growind plants, dead plant material, or chunks of soil called "clods." Another method is the use of windbarriers. Windbarriers protect the soil from wind erosion by reducing the speed of the wind as it passes over the soil. To find better designs for windbarriers we constructed 16 different windbarriers of plastic pipes (0.91 inches in diameter and 3.3 feet long) by suspending the pipes between two cables so the pipes were upright and the bottom of the pipes rested on the soil. We found that of the 16 types of windbarriers tested, the one that best reduced wind speed was a one-row barrier that had a 0.23-inch gap between all the pipes. It reduced the wind speed an average of 32% for a distance of 98 feet downwind from the barrier; that is, it was a very effective windbarrier. From all of the information that we obtained, we were able to find mathematical equations that would enable researchers to predict the amount of wind reduction produced by one, two, four, and eight-row windbarriers that had various-sized gaps between the pipes. This information will help people design more efficient windbarriers for reducing wind erosion.

Technical Abstract: To facilitate windbarrier modeling and designing, additional information is needed on the relationships of windbarrier conformation and wind velocity patterns. Therefore, we studied the effects of plastic pipe [diameter=2.31cm (0.91in), height=1m (3.3ft)] windbarriers on velocity patterns from 16 windbarrier configurations: 1, 2, 4, and 8 rows [row spacing=1m (3.3ft)] with optical densities (OD) of 12.5, 25, 50, and 75%. We found an equation that accurately describes (r^2's of 0.91 to 0.97) the relationships for density indexes (DI), percent of upwind velocity (PUV), and distances from R1 for the 1, 2, 4, and 8-row windbarriers (DI=optical density times number of rows in the windbarrier; R1 is downwind-most row). As the distance from R1 increased (upwind to 10h or downwind to 30h), PUV generally increased. As indicated by an efficiency index (EI=weighted average of reduction in downwind velocities) of 32.5, one row with OD=75 was the most effective in reducing downwind velocity; and the least efficient was a one-row windbarrier with OD=12.5 which had an EI of 4.3. The data showed that when OD was 12.5 or 25, EI increased as the number of rows increased. When OD was 50, EI increased for row numbers of one, two, and four, but decreased when row number was increased to eight. When OD was 75, EI decreased as row number was increased. These and other presented data should be useful in designing windbarrier systems or modeling their effects on wind velocity patterns.

Last Modified: 10/1/2014
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