AGNPS is a tool for use in evaluating the effect of management decisions impacting a watershed system. The AGNPS system is a direct update of the AGNPS 98 & 2001 system of modules containing many enhancements.

The term "AGNPS" now refers to the system of modeling components instead of the single event AGNPS, which was discontinued in the mid-1990's. These enhancements have been included to improve the capability of the program and to automate many of the input data preparation steps needed for use with large watershed systems.

New to AnnAGNPS Version 5.00, the model includes enhanced ephemeral gully feature, automated calibration features for many of the pollutants, capabilities to enter in an unlimited number of climate stations with any naming convention needed, actual or potential evapotranspiration for every climate station can now be defined in any climate file, and many more input and output options. The AGNPS interface has been better integrated with the components needed to develop AnnAGNPS datasets, including the development of automated procedures for the creation of ephemeral gully input data. The capabilities of RUSLE, used by USDA-NRCS to evaluate the degree of erosion on agricultural fields and to guide development of conservation plans to control erosion, have been incorporated into AnnAGNPS. The capability of importing RUSLE2 databases into AnnAGNPS is also available. This provides a watershed scale aspect to conservation planning. The channel network evolution models, CCHE1D, and the stream corridor model CONCEPTS, have been developed for analysis of reaches within a stream network for integration with AnnAGNPS, for watersheds that require a more comprehensive evaluation of the stream system, when channel evolution, erosion, or in-stream structures produce problems that the simplified channel system of AnnAGNPS is not designed for. An updated output processor now provides convenient compilation of loadings at any point in the watershed on an event, monthly or annual basis. The output processor includes options to determine the flow associated with a runoff hydrograph distributed across days, as well as associated with individual events.

The input programs include: (1) a GIS-assisted computer program (TOPAZ with an interface to AGNPS) to develop terrain-following cells with all the needed hydrologic & hydraulic parameters that can be calculated from readily available DEM's. Included are procedures to associated management, soils, and climate shape files with the derived AnnAGNPS cells. Additional features of the GIS interface provide ephemeral gully input information required by AnnAGNPS to describe the location of gully mouths and the associated input information for each gully; and (2) an Input Editor to initialize, complete, and/or revise the input data. Options are now available in the Input Editor to export and import files in a comma-delimited format for many of the data sections. This provides a convenient approach to developing input data sections in spreadsheet programs and then importing those into the Input Editor.

AnnAGNPS includes up-to-date technology (e.g., ephemeral gullies, RUSLE & pesticides) as well as the daily features necessary for continuous simulation in a watershed.

Outputs related to soluble & attached nutrients (nitrogen, phosphorus, & organic carbon) and any number of pesticides are provided. Water and sediment yield by particle size class and source are calculated. A field pond water & sediment loading routine is included for rice/crawfish ponds that can be rotated with other land uses. Nutrient concentrations from feedlots and other point sources are modeled. Individual feedlot potential ratings can also be derived using the model. The application of CCHE1D for stream networks and CONCEPTS for stream corridors include more detailed science for the channel hydraulics, morphology, and transport of sediments and contaminants.