Model (AnnAGNPS) is a continuous simulation watershed-scale program. It is an expansion of the capabilities in the single event model AGNPS. It is the pollutant loading model in the suite of models for AGNPS. To use AnnAGNPS, the watershed is subdivided into homogenous land areas with respect to soil type, land use, and land management. Areas can be of any shape including hydrologically-based or square grid (as was used in AGNPS). AnnAGNPS simulates quantities of surface water, sediment, nutrients, and pesticides leaving the land areas (cells) and their subsequent travel through the watershed. Some of the sediment, nutrients, and pesticides will reach the watershed outlet while the remainder will be deposited in the stream system. Calculations are done on a daily time step. Runoff quantities are based on runoff curve number while sheet & rill sediment is determined using RUSLE. Special components are included to handle concentrated sources of nutrients (feedlots and point sources), ephemeral gully sources, concentrated sediment sources (classical gullies), and added water (irrigation). Output is expressed on an event basis for selected stream reaches and as source tracking (contribution to outlet) from land or reach components over the simulation period.
