Conceptually the system can be viewed as consisting of three parts: Data Preparation; Simulation Processing; and Output. Data Preparation encompasses: reading in data; error checking; setting internal pointers; establishing internal array sizes based on data read; initializing data required for the simulation (developing climate normals; soil compositing; determining cell & reach time of concentrations; establishing reach routing order and reach drainage areas, RUSLE preprocessing, and pre-simulation initialization). Simulation processing includes processing climate information for each day of the simulation period and its impact on cells, feedlots, gullies point sources and reaches. Information concerning soil moisture, snow pack, crop growth, residue and chemicals are carried from one day to the next for each cell as are manure pack and nutrients for each feedlot. Output data are also accumulated from the events during the simulation processing. Average annual output analyzes variable accumulations over the simulation period at downstream reach locations to determine contributions from specific user selected components (cell, feedlot, gully, point source, or reach). Variables analyzed are user selected from input source accounting flags or global source accounting flags.