Brief introduction to the Revised Universal Soil Loss Equation.

The results of the statistical analysis of about 10000 plot years of data was used in developing what is now a well known model for sheet and rill soil loss prediction called the Universal Soil Loss Equation. Soil loss equations are empirical (based on field collected data) models developed to enable conservation planners to project limited erosion data to the many localities and conditions that have never been directly analyzed. The Revised USLE was developed by the USDA Agricultural Research Service (internet link) to further extend the USLE (prepared for croplands) to wild areas of rangelands, particularly in arid and semi-arid climates. The RUSLE reflects the basic USLE structure:

A = R * K * L * S * C * P

Where:

• A is the computed soil loss per unit area, usually in tons per acre per year;
• R is the rainfall and runoff factor and is the number of rainfall erosion index units;
• K is the soil erodibility factor, is the soil loss rate per erosion index unit for a specified soil as measured on a unit plot, which is defined as a 72.6-ft length of uniform 9-percent slope continuously in clean tilled fallow;
• L is the slope-length factor, is the ratio of soil loss from the field slope length to that from a 72.6-ft length under identical conditions;
• S is the slope-steepness factor, is the ratio of soil loss from the field slope gradient to that from a 9-percent slope under otherwise identical conditions;
• C is the cover and management factor, is the ratio of soil loss from an area with specified cover and management to that from an identical area in tilled continuous fallow;
• P is the support practice factor, is the ratio of soil loss with a support practice like contouring, stripcropping, or terracing to that with straight-row farming up and down the slope.

Resource Notes:

• Regional sheet and rill soil erosion prediction with the Revised Universal Soil Loss Equation (RUSLE) – GIS Interface

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Software Downloads:

RUSLE.EXE

This program uses your input regarding the physical characteristics of the field sized area for which you wish to estimate annual soil loss in tons/acre/year and/or sediment yield in metric tons for a given storm. The Universal Soil Loss Equation (USLE) was developed by Wischmeier and Smith and is described in USDA Agriculture Handbook #537 (1978). The USLE revision (RUSLE) is intended to provide more accurate estimates of erosion from wildlands, specifically western rangelands. The major revisions occur in the 'C', 'P', and 'LS' factors. The 'C' or cover-management factor is now the product of 4 sub-factors: PRIOR LAND USE - CANOPY COVER - SOIL SURFACE COVER and SURFACE ROUGHNESS. The sub-factor algorithms are based on work of J.M. Laflen of the U.S. Dept. of Agriculture-Agricultural Research Service (USDA-ARS). The algorithms are based on rainfall simulator data obtained from rangeland areas in the western United States. The 'P' factor or erosion control practice is based on surface conditions and runoff reductions after an improvement practice has been imposed. 'P' factor values for rangelands were estimated by G.R. Foster and K.G. Renard, both of USDA-ARS. The (LS) factor or slope length and steepness factor is based on interactions between slope length and steepness and was quantified for rangelands by D.K. McCool and G.R. Foster, both of USDA-ARS.

User inputs for both the RUSLE are: Field location (latitude & longitude), Soil properties (particle size, percent organic matter, soil structure, and permeability), field vegetation canopy cover, ground surface cover, management system or use, roughness, and productivity. If erosion control practices are used, their effects are also considered in the soil loss estimate.

&r LSFACTOR <input DEM> <cell size>

This AML calculates the RUSLE terrain (LS) factor from Digital Elevation Model data using two methods, one developed by for the DOS RUSLE program discussed above (look up RUSLE.BAS), and on the method suggested by Mitasova (1993) and based on work of Ion Moore (1992). See illustrations below:

&r ITEMGRID <in_coverage> <out_grid> <cellsize> <feature_class>

This AML converts a vector coverage into a grid while permitting interactive selection of the item to be converted from a popup window. Can be used for converting specific items, such as the RUSLE soil erodibility (K) factor from the attribute table of a soils coverage.