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ARS Home » Southeast Area » Oxford, Mississippi » National Sedimentation Laboratory » Watershed Physical Processes Research » Research » Publications at this Location » Publication #116713
Title: ANNAGNPS: ESTIMATING SEDIMENT YIELD BY PARTICLE SIZE FOR SHEET AND RILL EROSION

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

Submitted to: Federal Interagency Sedimentation Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/26/2001
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 soil erosion from farms is essential in estimating the downstream impact on water quality. Technology is described in this study that can be used to provide the link between the soil erosion leaving the agricultural fields and the sediment loadings downstream in the rivers of a watershed. This technology is important to local, state, and federal watershed management planners who are required to determine the impact non-point source pollution from agricultural 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 the sediment yield (clay, silt, and sand) from the watershed landscape by AnnAGNPS, which is a continuous-simulation, agricultural-related, non-point source, pollutant loading watershed model. The fine sediment yield (clay and silt) from sheet and rill erosion of agricultural lands is a major concern for pollutant loadings into water bodies, such as streams and channels. A simple procedure to estimate the sediment delivery by particle size is necessary to link the sheet and rill erosion to the sediment yield in water bodies. Determining the sediment yield by particle size from each homogenous land area within the watershed (defined as a cell in AnnAGNPS) is critical in assessing the effectiveness of best management practices. The application of RUSLE is used to determine where and when sheet and rill erosion can occur. Algorithms within RUSLE for irregular and segmented slopes are defined in the USDA Agricultural Handbook Number 703, and can be used to determine a raster- weighted LS-factor for each homogenous land area. The delivery ratio procedure in AnnAGNPS is based upon HUSLE (Hydro-geomorphic Universal Soil Loss Equation) and the respective fall velocities of the particle-size classes predicted by RUSLE. The results show that most coarse sediment (sand-size particles) deposit in the fields while most fine sediments (eroded clay and silt size particles that become entrained in the runoff) become wash load and enter the streams and channels.