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ARS Home » Southeast Area » Oxford, Mississippi » National Sedimentation Laboratory » Watershed Physical Processes Research » Research » Publications at this Location » Publication #116034
Title: TOPOGRAPHIC FACTORS FOR RUSLE IN THE CONTINUOUS-SIMULATION, WATERSHED MODELFOR PREDICTING AGRICULTURAL, NON-POINT SOURCE POLLUTANTS (ANNAGNPS)

Author
item Bingner, Ronald - Ron
item THEURER, FRED - NRCS

Submitted to: Soil Erosion for 21st Century Symposium
Publication Type: Proceedings
Publication Acceptance Date: 1/4/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary: Eroded soil from agricultural fields is a major pollutant entering the streams and rivers of the United States. An accurate determination of the topography of the land is essential in estimating how much soil is leaving a field. Technology was developed in this study to determine the field slope and length parameters needed for calculating soil erosion using readily available topographic information. An easy and automatic procedure was developed to improve and encourage the adoption of erosion technology in assessing and planning agricultural management practices. This technology is important to local, state, and federal watershed management planners who are required to determine the impact non-point source pollution from watersheds has on the impairment of rivers and streams.

Technical Abstract: RUSLE (Revised Universal Soil Loss Equation) is the basis within AnnAGNPS (Annualized Agricultural Non-Point Source Pollution watershed model) for estimating sheet and rill erosion (clay, silt, sand, small and large aggregates) of a watershed's landscape. This sheet and rill erosion is used to predict fine sediment yield (clay and silt) from the watershed landscape by AnnAGNPS, which is a continuous-simulation, agricultural- related, non-point source, pollutant loading, watershed model. The fine sediment yield from sheet and rill erosion of agricultural lands generally is a major concern for pollutant loadings within water bodies. Other sources of sediment (gullies and bed and bank erosion) are also predicted by AnnAGNPS, but only RUSLE is used to estimate the sheet and rill erosion. The RUSLE topographic factor (LS-factor) is time invariant and can be determined directly from digital elevation models (DEMs). The purpose of AnnAGNPS is to predict expected pollutant loading for each storm event - not a conservative estimate along a critical profile in the field. Therefore, it is important to determine the LS-factor for each homogenous land areas within the watershed (a cell in AnnAGNPS) to reproduce the expected erosion for a homogenous land area if the other RUSLE parameters are known. The topographic factor routine for AnnAGNPS follows each DEM raster along its respective flow path and recognizes where and when sheet and rill can occur. By using the slope length and steepness factor algorithms for irregular and segmented slopes, a raster- weighted LS-factor for each homogenous land area can be determined. The accuracy of the resulting LS-factors are a function of the horizontal and, in particular, the vertical raster resolution of the DEM.