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United States Department of Agriculture

Agricultural Research Service

Title: Validation of the Wind Erosion Equation (Weq) for Discrete Periods of the Wind Erosion Stochastic Simulator (Wess) for Single Events

Authors
item Van Pelt, Robert
item Zobeck, Teddy
item Potter, Kenneth

Submitted to: American Society of Agricultural Engineers Meetings Papers
Publication Type: Proceedings
Publication Acceptance Date: September 7, 2000
Publication Date: N/A

Interpretive Summary: The Wind Erosion Equation (WEQ) is used by the USDA Natural Resources Conservation Service (NRCS), formerly know as the Soil Conservation Service (SCS), to predict the wind erosion from farm fields. This predicted wind erosion is compared to tables for allowable erosion to determine if a given farmer is complying with regulatory guidelines. WEQ was developed 35 years sago and several NRCS employees have expressed concern with the accuracy of its predictions. The Wind Erosion Stochastic Simulator (WESS) is a stand-alone wind erosion model extracted from the Environmental Policy Integrated Climate (EPIC) erosion model that has also been used to assess field management with regulatory compliance. During the last 11 years, development of two new wind erosion models by USDA-ARS personnel has required the collection of several large databases of wind erosion measurements in diverse locations of the United States. We tested the predictions that WEQ would make for specific fields in these locations against the erosion measured at these locations. We found that WEQ under- predicted erosion by as much as a factor of nine in certain locations and only did a good job of predicting erosion in western Kansas and Eastern Colorado. From working with the input factors, we determined that the C factor needs to be adjusted upward for many locations. We tested the predictions of WESS against measured erosion for 24 dust storms at Big Spring, Texas. WESS under-estimated the erosion for 9 storms, accurately predicted the erosion for 8 storms, and over-predicted the erosion for 7 storms. WESS tended to under-predict the erosion from large storms and over-predict the erosion form very small storms. Overall, WESS would tend to under-estimate the erosion on an annual basis.

Technical Abstract: The Wind Erosion Equation (WEQ) is currently used by the United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) to ensure compliance with government guidelines for soil loss from agricultural land. The Wind Erosion Stochastic Simulator (WESS) is a single event wind erosion model that is the core of the wind erosion submodel of the Environmental Policy Integrated Climate (EPIC) erosion model. In this study we compared estimates of wind erosion derived from the sums of field measurements at seven locations, two of which had multiple years of observations (a total of 14 periods of comparison), with the predictions of WEQ. We also compared estimates of wind erosion at multiple points in a field for 24 events at Big Spring, Texas with the predictions of WESS. Overall, WEQ predicted only 53 % of the total observed erosion for the fourteen periods. WEQ underestimated 11 of the 14 4periods investigated. by as much as a factor of nine and of the three periods WEQ over-estimated, the maximum factor was less than 1.5. WESS under-predicted 9 events, accurately predicted 8 events, and over-predicted 7 events. WESS tends to under-estimate large magnitude storms and over-estimate very small magnitude storms, therefore, WESS would tend to under-estimate annual erosion.

Last Modified: 10/21/2014
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