Assumptions and Estimation of USLE Parameters

 Wischmeier (1976) reported that the USLE may be used to predict the average- annual soil loss from a field-sized plot with specified land use conditions (Mitchell and Bubenzer 1980). The assumptions associated with the USLE are as follows (Goldman et. al. 1986; Novotny and Chesters 1981; Foster 1976; Onstad and Foster 1975):

  • The USLE is an empirically derived algorithm and does not mathematically represent the actual erosion process.
  • The USLE was developed to estimate long-term, average-annual, or seasonal soil loss. Unusual rainfall seasons, especially higher than normal rainfall, and typically heavy storms may produce more sediment than estimated.
  • The USLE estimates soil loss on upland areas only; it does not estimate sediment deposition. Sediment deposition generally occurs at the bottom of a slope (i.e., change in grade) where the slope becomes milder.
  • The USLE estimates sheet, rill, and inter-rill erosion and does not estimate channel or gully erosion. Gully erosion, caused by concentrated flows of water, is not accounted for by the equation and yet can produce large volumes of eroded soil.
  • The USLE was developed originally to address soil loss from field-sized plots, although with proper care, watersheds can be addressed.
  • Because the USLE only estimates the volume of sediment loss (i.e., the volume of soil detached and transported some distance), it can be used to estimate sediment transport capacity at a site.
  • Because the USLE represents an empirically derived expression, consistently accurate estimates of soil loss are fortuitous at best.
  • The USLE does not estimate soil loss from single storm events unless a modified form of the original equation is used.

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