| Describe available calibration data sets
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SPF and the earlier models from which it was developed have been extensively
applied in a wide variety of hydrologic and water quality studies (3,4),
including pesticide runoff model testing (5), aquatic fate and transport
model testing (6,7), and analyses of agricultural best management practices
(8,9). An application of HSPF in a screening methodology for pesticide
review is described by Donigian et al. (10). In addition, HSPF has been
validated with both field data and model experiments, and has been reviewed
by independent experts (11-20).
The Stream Transport and Agricultural Runoff for Exposure Assessment
Methodology (STREAM) applies the HSPF program to various test watersheds for
five major crops in four agricultural regions in the United States,
defines a "representative" watershed based on regional conditions and an
extrapolation of the calibration for the test watershed, and performs a
sensitivity analysis on key pesticide parameters to generate cumulative
frequency distributions of pesticide loads and concentrations in each
regions. The resulting methodology requires the user to evaluate only the
crops and regions of interest, the pesticide application rate, and three
pesticide parameters -- the partition coefficient, the soil/sediment decay
rate, and the solution decay rate.
The EPA Chesapeake Bay Program has been using the HSPF model as the framework
for modeling total watershed contributions of flow, sediment, and nutrients
(and associated constituents such as water temperature, DO, BOD, etc.) to the
tidal region of the Chesapeake Bay (21,22). The watershed modeling
represents pollutant contributions from an area of more than 68,000 sq. mi.,
and provides the input to drive a fully dynamic three-dimensional,
hydrodynamic/water quality model of the Bay. The watershed drainage area is
divided into land segments and stream channel segments. The land areas
modeled include forest, agricultural cropland (conventional and conservation
tillage systems), pasture, urban (pervious and impervious areas), and
uncontrolled animal waste contributions. The stream channel simulation
includes flow routing and oxygen and nutrient biochemical modeling (through
phytoplankton) in order to account for instream processes affecting nutrient
delivery to the Bay.
Currently, buildup/washoff type algorithms are being used for urban
impervious areas, potency factors for all pervious areas, and constant (or
seasonally variable) concentrations for all subsurface contributions and
animal waste components. Enhancements are underway to utilize the detailed
process (i.e. Agrichemical modules) simulation for cropland areas to better
represent the impacts of agricultural BMPs and to include nitrogen cycling in
forested systems to evaluate the impacts of atmospheric deposition of
nitrogen on Chesapeake Bay. The watershed modeling is being used to evaluate
nutrient management alternatives for attaining a 40% reduction in nutrient
loads delivered to the Bay, as defined in a joint agreement among the
governors of the member states.
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