ANSWERS-2000 is a distributed parameter, physically-based, continuous simulation, watershed scale, upland planning model developed for evaluating the effectiveness of agricultural and urban BMPs in reducing sediment and nutrient delivery to streams in surface runoff and leaching of nitrogen through the root zone. The model is intended for use by planners on ungaged watersheds where data for model calibration is not available. The model divides the area simulated into a uniform grid of square (1 hectare or smaller), within which all properties (surface and subsurface soil properties, vegetation, surface condition, crop management, and climate) are assumed homogeneous. The model uses breakpoint precipitation data and simulates hydrologic processes with a 30-second time step during runoff events and with a daily time step between runoff events. The model simulates interception; surface retention/detention; infiltration; percolation; sediment detachment and transport of mixed particle size classes in rills, interrill areas, and channels; crop growth; plant uptake of nutrients; N and P dynamics in the soil; nitrate leaching; and losses of nitrate, ammonium, total Kjeldahl nitrogen, and P in surface runoff as affected by soil, nutrient, cover and hydrologic conditions. The model has an ArcView based user interface, QUESTIONS, that facilitates data file creation and manipulation. Model documentation and user support is very limited.  The model is currently only suitable for use by expert modelers with a good knowledge of upland hydrology and agriculture.  The current version of the model makes heavy use of relationships derived from the WEPP and EPIC models.

Hydrologic Processes Simulated by ANSWERS-2000



BSE Department

 Maintained by Theo Dillaha, Professor of Biological Systems Engineering,
Virginia Tech, Blacksburg, VA 24061-0303,
Phone: 540-231-6813, Fax: 540-231-3199, E-mail:
 copyright ⓒ 2003 Biological Systems Engineering Dept at Virginia Tech. All Rights Reserved.

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