SWAT is a quasi physically-based water quality simulation model that operates on a daily time step. SWAT was developed to predict the impact of land management practices on water, sediment and agricultural chemical yields in large complex watersheds with varying soils, land use and management conditions over long periods of time.
Water balance is the driving force behind everything that happens in a watershed.
To accurately predict movement of sediment, nutrients and pesticides, the hydrologic cycle as simulated by the model must conform to what is happening in the watershed. For simulations the watershed of interest is subdivided into simulation elements, either grid cells, virtual basins or subbasins. For each simulation element water flux and transport of sediment and agrichemicals are simulated and then routed through a watershed, i.e., water and chemicals are transported from one simulation element to the next depending on flow characteristics. An integrated user interface for SWAT using ArcView and Avenue. Neitsch, S.L., J.G., Arnold and J.R., Williams. 1999.