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United States Department of Agriculture

Agricultural Research Service

Soil Resources & Air Quality Affected by Wind Erosion and Fugitive Dust Emissions
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1 - Wind Erosion - The Problem
2 - The Wind Erosion Prediction System (WEPS)
3 - The Old Wind Erosion Equation (WEQ)
4 - Particulate Matter (PM-10)
5 - Recent Wind Erosion Publications
6 - Videos - Erosion Caused by Wind
The Old Wind Erosion Equation (WEQ)


 

Introduction 

Although many of the principles of wind erosion were known before the 1930's, the foundations of modern wind erosion prediction technology largely began with the publication in 1941 of Ralph Bagnold's classic book titled "The Physics of Blown Sand and Desert Dunes". Further research was needed for application to agricultural fields, which are generally more complicated than sand dunes.  The complications include properties that change over time such as soil, aggregate size and stability, crusts, random and oriented roughness, field size, and vegetative cover.


 A history of the old WEQ prediction model was published in Aeolian Research

The Wind Erosion Equation (WEQ)
  
Using wind tunnels and field studies, the late Dr. William S. Chepil and co-workers set out in the mid-1950's to develop the first wind erosion prediction equation (WEQ) which was used by the Natural Resources Conservation Service (NRCS) and other action agencies throughout the country until recently.


WEQ has since been replaced by the more user friendly, processed based Wind Erosion Prediction System (WEPS).  WEPS represents a significant science improvement to predict wind erosion on site and quantify the offsite movement of soil to include PM-10 (particulate matter less than 10µm in size). 

Because field erodibility varies with field conditions, a procedure to solve WEQ for periods of less than one year was devised. In this procedure, a series of factor values are selected to describe successive management periods in which both management factors and vegetative covers are nearly constant.

 
Dr. Chepil and the Wind Erosion Tunnel located at
Kansas State University  - photo courtesy USDA-ARS-CGAHR

Erosive wind energy distribution is used to derive a weighted soil loss for each period. Soil loss for the management periods over a year are added to estimate annual erosion. Soil loss from the periods also can be added for a multi-year rotation, and the loss divided by the number of years to obtain an average, annual estimate.

WEQ was a widely used method (Excel Spreadsheet) for assessing average annual soil loss by wind from agricultural fields. The primary user of WEQ was the Natural Resources Conservation Service (NRCS). When WEQ was developed approximately 40 years ago, it was necessary to make it a simple mathematical expression, readily solvable with the computational tools available. However, WEQ had fundamental weaknesses because of its equation structures and its empirical representation of erosion processes. Since its inception, there have been a number of efforts to improve the accuracy, ease of application, and range of WEQ. Despite efforts to make such improvements, the structure of WEQ precluded adaptation to many problems. 

In 1986, the USDA began a more than 20-year effort to develop the next generation of wind erosion prediction technology.  The NRCS began using WEPS in its field offices in 2010. Find out more information on WEPS here.
   

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Last Modified: 3/25/2014
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