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In addition, the model considers point sources of water, sediment, nutrients, and chemical oxygen demand (COD) from animal feedlots, and springs. Water impoundments, such as tile-outlet terraces, also are considered as depositional areas of sediment and sediment-associated nutrients.
The model has the ability to output water quality characteristics at intermediate points throughout the watershed network. This capability is based on the model's implementation of the 'cell'. Cells are uniformly square areas subdividing the watershed, and all watershed characteristics and inputs are expressed at the cell level.
Model components use equations and methodologies that have been well established and are extensively used by agencies such as the USDA Soil Conservation Service. Runoff volume and peak flow rate are estimated using the SCS runoff curve number method. Peak runoff rate for each cell is estimated using an empirical relationship proposed by Smith and Williams (1980) and which is also used in CREAMS (Frere et al., 1980).
Upland erosion and sediment transport is estimated using a modified form of the Universal Soil Loss Equation, USLE (Wischmeier and Smith, 1978). Sediment is routed from cell to cell through the watershed to the outlet using a sediment transport and depositional relationship described by Foster et al. (1981) which is based on a steady-state continuity equation. Chemical transport is calculated based on the relationships adapted from CREAMS and a feedlot evaluation model (Young et al., 1982).
Feedlots are treated as point sources and chemical contributions are estimated using the feedlot pollution model developed by Young et al. Other point-source inputs of water and nutrients, such as springs, and wastewater concentrations of nutrients to the cells where they occur. |
