for simulation of watershed hydrology and water quality for both conventional
and toxic organic pollutants (1,2). This model can simulate the hydrologic,
and associated water quality, processes on pervious and impervious land
surfaces and in streams and well-mixed impoundments. HSPF incorporates the
watershed-scale ARM and NPS models into a basin-scale analysis framework that
includes fate and transport in one-dimensional stream channels. It is the
only comprehensive model of watershed hydrology and water quality that allows
the integrated simulation of land and soil contaminant runoff processes with
in-stream hydraulic and sediment-chemical interactions.
The result of this simulation is a time history of the runoff flow rate,
sediment load, and nutrient and pesticide concentrations, along with a time
history of water quantity and quality at any point in a watershed. HSPF
simulates three sediment types (sand, silt, and clay) in addition to a single
organic chemical and transformation products of that chemical. The transfer
and reaction processes included are hydrolysis, oxidation, photolysis,
biodegradation, volatilization, and sorption. Sorption is modeled as a
first-order kinetic process in which the user must specify a desorption rate
and an equilibrium partition coefficient for each of the three solids types.
Resuspension and settling of silts and clays (cohesive solids) are defined in
terms of shear stress at the sediment water interface. The capacity of the
system to transport sand at a particular flow is calculated and resuspension
or settling is defined by the difference between the sand in suspension and
the transport capacity. Calibration of the model requires data for each of
the three solids types. Benthic exchange is modeled as sorption/desorption
and deposition/scour with surficial benthic sediments. Underlying sediment
and pore water are not modeled.
program and requires continuous data to drive the simulations. At a minimum,
continuous rainfall records are required to drive the runoff model and
additional records of evapotranspiration, temperature, and solar intensity
are desirable. A large number of model parameters can be specified although
default values are provided where reasonable values are available. HSPF is
a general-purpose program and special attention has been paid to cases where
input parameters are omitted. In addition, option flags allow bypassing of
whole sections of the program where data are not available.
nutrient and pesticide concentrations, along with a time history of water
quantity and quality at any point in a watershed. Simulation results can be
processed through a frequency and duration analysis routine that produces
output compatible with conventional toxicological measures (e.g., 96-hour
appropriate for the area being modeled. Further, the instream model assumes
the receiving water body is well-mixed with width and depth and is thus
limited to well-mixed rivers and reservoirs. Application of this methodology
generally requires a team effort because of its comprehensive nature.
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.
HSPF_V11.004, HSPF_V11.005, HSPF_V11.006, and HSPF_V11.007 in the DOCUMENT
sub-directory. Refer to file READ.ME in the README sub-directory for further
information on the storage format and printing requirements of the user's
This part will be filled out by CSDMS staff