| dc.description.abstract | This article briefly reviews the hydrologic components of prominent models used in agricultural and mixed land
use watersheds and presents the current state‐of‐the‐art in agricultural watershed modeling. The models included are
Annualized Agricultural Nonpoint Source (AnnAGNPS), Areal Nonpoint Source Watershed Environment Response
Simulation (ANSWERS‐2000), Hydrologic Simulation Progr
am - Fortran (HSPF), Soil and
Water Assessment Tool (SWAT),
Watershed Assessment Model (WAM), and Water Erosion Prediction Project (WEPP). Hydrologic components
(e.g., precipitation, potential evapotranspiration (PET), infiltration‐surface runoff, groundwater, and stream flow) are
discussed for
each of these models. Simulation of PET differs among selected watershed models, with some offering multiple
PET options and others pr
oviding one method. The primary difference in the infiltration and surface runoff algorithms among
watershed models is their empirical (e.g., curve number (CN) and Green‐Ampt) or physical (e.g., Philip's) basis and their
simulation time step. Groundwater components (such as interflow, tile drainage, shallow aquifer, and deep aquifer) may be
one of the most variable hydrologic components among watershed models. Stream flow was routed predominantly by the
selected models using the continuity equation and Manning's equation; other algorithms used were the Muskingum routing
method, finite difference integration, and kinematic wave. The use of watershed models by agricultural and biological
engineers continues to expand as new technologies, such as the integration of remote sensing and Geographic Information
Systems (GIS), and computer capabilities improve and the expectations for high‐quality results (including uncertainty
analyses and multi‐objective functions) increase | en |
