animal waste application methods on water quality. The SWRRB model has been used on several
watersheds to assess management practices and to test its validity (Arnold and Williams, 1987; Bingner
et al., 1987).
AGNPS (Young et al. 1994) is a spatially-distributed model for estimating pollutant runoff from
agricultural watersheds. Within cells, the model can evaluate practices such as feedlot management,
terraces, vegetative buffers, grassed waterways, and farm ponds. Simulated nutrient, sediment, and
pesticide concentrations and yields are available for any cell within the watershed. The AGNPS model
has been applied to many field and watershed size areas to estimate pollutant runoff from various land
uses and management practices (Line et al., 1997: Sugiharto et al., 1994; Bingner et al., 1987)
ANSWERS (Beasley, 1980) is a spatially-distributed watershed model. The model is primarily
a runoff and sediment model as soil nutrient processes are not simulated. The ANSWERS model has
been applied to several small fieldsized areas with various management practices (Griffin et al., 1988;
Bingner et al., 1987).
NTRM (Shaffer and Larson, 1985) simulates the impact of soil erosion on the short and long-
term productivity of soil, and is intended to assist with evaluation of existing and proposed soil
management practices in the subject areas of erosion, soil fertility, tillage, crop residues, and irrigation.
The NTRM model has been applied to evaluate effects of conservation tillage, supplemental nitrogen
and irrigation practices (Shaffer, 1985) and moldboard plow and chisel plow tillage (Shaffer et al.,
1986) on soil erosion and productivity. This model has had limited use.
A series of protocols has been developed by EPA to assist in the development of TMDLs and
implementation plans to achieve the TMDLs (EPA, 1997 - DRAFT at this point). These protocols
focus primarily on the application of computer models that simulate watershed conditions and the
changes that could result from implementation of various land management scenarios. Most models
contain default values for the quantity of pollutants that are delivered in runoff.
Arnold, J. G. and R. R. Williams. 1987. "Validation of SWRRB - Simulation for Water Resources
in Rural Basins. J. Water Resources Planning and Management 13:243-256.
Arnold, J. G., J. R. Williams, A. d. Nicks, and N. B. Sammons. 1990. SWRRB: A Basin Scale
Simulation Model for Soil and Water Resources management. Texas A&M University Press, College
Station, Texas.
Bannerman et al. 1983. "Sources of Pollutants in Wisconsin Stormwater," Water Sci. Technol.


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