The WEQ (Wind Erosion Equation) was reported by Woodruff and Siddoway in 1965. WEQ utilized the available technology to estimate annual soil erosion with different management systems. WEQ was developed using laboratory and field wind tunnel data but had little supporting field data of erosion from natural wind storms. WEQ computes only the average annual soil erosion, not daily, monthly, or other periods of time. To determine transport mass the length of the field must be included. Some changes in WEQ were made after 1965, but no field data were available to support or confirm that the changes were scientifically correct or valid.
The RWEQ (Revised Wind Erosion Equation) was reported in 1998 (by Fryrear et. al.). RWEQ incorporated advances in wind erosion science after 1965. The various components of RWEQ were developed from controlled laboratory and field studies, but the actual transport model was calibrated using field data of transport mass. From the transport mass and field length, the average soil erosion can be determined. Once the transport mass equation was developed, transport mass could be estimated for any site where wind erosion was a significant problem. Actual field transport mass was used to test RWEQ in a wide variety of field conditions in 20 states. RWEQ field data were collected in regions with 191 to 1255 mm annual rainfall, and the elevation at the validation sites varied from 141 to 1341 m. Sand content in the surface soil varied from 10 to 87%. Erosion measurement periods were from three to thirty-six months. While the majority of the sites were 2.6 ha. circles other sites were a 52 ha. circle and 36 to 128 ha. rectangular fields.
Using the RWEQ model the effects of various cropping systems, wind barriers, soil roughness, hills, and residue management schemes can be tested to determine the daily, weekly, or annual erosion. In addition, the daily transport mass can be used to identify periods when crop injury is most likely to occur, and the protection required. The RWEQ model will operate with a minimum of input data, but to give good estimates of soil erosion it requires good weather data.