Universal Soil Loss

Universal soil loss equation (USLE) is a widely used empirical model that estimates long-term soil erosion caused by rainfall and surface runoff.  It helps predict the average rate of soil erosion per unit area over a given time period.  The equation is commonly applied in agriculture, land management, and conservation planning to assess the potential for soil loss and to design practices to minimize erosion.

Application

Agriculture  -  Helps farmers and land managers determine the need for erosion control measures.
Urban Planning  -  Assists in land-use planning to minimize soil loss during construction and development.
Environmental Conservation  -  Guides efforts to maintain soil health and prevent land degradation.

 

Universal Soil Loss Formula
\( USL \;=\;  R \; K \; L \; S \; C \; P  \)     (Universal Soil Loss) \( R \;=\;  USL \;/\; K \; L \; S \; C \; P  \) \( K \;=\;  USL \;/\; R \; L \; S \; C \; P  \) \( L \;=\;  USL \;/\; R \; K \; S \; C \; P  \) \( S \;=\;  USL \;/\; R \; K \; L \; C \; P  \) \( C \;=\;  USL \;/\; R \; K \; L \; S \; P  \) \( P \;=\;  USL \;/\; R \; K \; L \; S \; C  \)
Symbol	English	Metric
\( USL \) = Average Annual Soil Loss	\(ton\;/\;Acre\)	\(hectare\;/\;Year\)
\( R \) = Rainfall and Runoff Factor	\(dimensionless\)	\(dimensionless\)
\( K \) = Soil Erodibility Factor	\(dimensionless\)	\(dimensionless\)
\( L \) = Slope Length Factor	\(dimensionless\)	\(dimensionless\)
\( S \) = Slope Steepness Factor	\(dimensionless\)	\(dimensionless\)
\( C \) = Cover and Management Factor	\(dimensionless\)	\(dimensionless\)
\( P \) = Support Practice Factor	\(dimensionless\)	\(dimensionless\)

 

Symbols

\(A \;=\;\) Average annual soil loss (tons per acre or hectare per year).  The predicted average annual soil loss in tons per acre per year from a given slope
\(R \;=\;\) Rainfall erosivity factor (measures the impact of rainfall intensity and duration).  It is a measure of rainfall energy and intensity rather than just rainfall amount.
\(K \;=\;\) Soil erodibility factor (indicates the susceptibility of soil particles to erosion).  It is a measure of the relative resistance of a soil to detachment and transport by water.
\(L \;=\;\) Slope length factor (represents the effect of slope length on erosion).  It is the expected ratio of soil loss from a given field slope to that from a slope 72.6 feet in length with a uniform slope of 9 percent.  Slope (L) is measured from the point of origin of overland flow to the point where deposition begins and/or where the water enters a defined channel. 
\(S \;=\;\) Slope steepness factor (represents the effect of slope gradient on erosion).  It is the ratio of soil loss from land cropped under specified conditions to the corresponding loss from clean-tilled, continuous fallow.  This factor measures the combined effect of all the interrelated cover and management variables
\(C \;=\;\) Cover and management factor (accounts for the type of vegetation or land cover and its ability to protect soil)  It is the ration of soil loss with a specific support practice to the corresponding soil loss with up-and-down hill culture.  Support practices include contouring and contour strip cropping.
\(P \;=\;\) Support practice factor (measures the impact of erosion control practices, such as contouring or terracing)  It is the ratio of soil loss with terraces to the soil loss without terraces and is based on relative sediment trapping efficiency.