Second Quarterly Progress Report October 2004
Limno-Tech, Inc. Page 9
continuous simulation basis, it is more amenable to site-specific calibration than USLE or
the WCS sediment tool.
Agricultural Nonpoint Source Pollution Model (AGNPS)
The Agricultural Nonpoint Source Pollution Model (AGNPS) is a joint USDA-Agricultural
Research Service and -Natural Resources Conservation Service system of
computer models developed to predict nonpoint source pollutant loadings within
agricultural watersheds. The sheet and rill erosion model internal to AGNPS is based
upon RUSLE, with additional routines added to allow for continuous simulation and
more detailed consideration of sediment delivery.
AGNPS was originally developed for use in agricultural watersheds, but has been
adapted to allow consideration of construction sources.
AGNPS provides more spatial detail than GWLF and is therefore more rigorous in
calculating the delivery of eroded sediment to the receiving water. This additional
computational ability carries with it the cost of requiring more detailed information
describing the topography of the watershed, as well as requiring more time to set up and
apply the model.
Hydrologic Simulation Program – Fortran (HSPF)
The Hydrologic Simulation Program – Fortran (HSPF) uses continuous rainfall and other
meteorologic records to compute stream flow hydrographs and pollutographs. HSPF is
well suited for mixed-use (i.e., containing both urban and rural land uses) watersheds, as
it contains separate sediment routines for pervious and impervious surfaces. HSPF is an
integrated watershed/stream/reservoir model, and simulates sediment routing and
deposition for different classes of particle size. HSPF was integrated with a geographical
information system (GIS) environment with the development of Better Assessment
Science Integrating point and Nonpoint Sources (BASINS). Although BASINS was
designed as a multipurpose analysis tool to promote the integration of point and nonpoint
sources in watershed and water quality-based applications, it also includes a suite of
water quality models. One such model is Nonpoint Source Model (NPSM). NPSM is a
simplified version of HSPF that is linked with a graphical user interface within the GIS
environment of BASINS. HSPC is another variant of the HSPF model, consisting of the
equations used by HSPF recoded into the C++ programming language.
HSPF provides a more detailed description of urban areas than AGNPS and contains
direct linkage to a receiving water model. This additional computational ability carries
with it the cost of requiring more detailed model inputs, as well as requiring more time to
set up and apply the model. BASINS software can automatically incorporate existing
environmental databases (e.g., land use, water quality data) into HSPF, although it is
important to verify the accuracy of these sources before using them in the model.
Storm Water Management Model (SWMM)
The Storm Water Management Model (SWMM) is a comprehensive computer model for
analysis of quantity and quality problems associated with urban runoff. SWMM is
designed to be able to describe both single events and continuous simulation over longer
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