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MS-DOSWindows |
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N/A |
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June 1993 |
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Yes (PDF) |
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USEPA |
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The U.S. Department of Agriculture's (USDA)
Simulator for Water Resources in Rural BasinsWater
Quality (SWRRBWQ) was originally developed by
Agriculture Research Service (ARS) and
Texas Agricultural Experiment Station.
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The model simulates
hydrologic, sedimentation, and nutrient and
pesticide transport in a large, complex rural
watershed. The model operates on a continuous
time-scale and allows for subdivision of basins to
account for differences in soils, land use,
rainfall, etc. It can predict the effect of
management decisions on water, sediment, and
pesticide yield with reasonable accuracy for
ungaged rural basins throughout the United States.
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SWRRB-WQ Windows Interface was developed by
U.S. EPA in June 1993. Pesticide, Soil and Rainfall Coverage is for the
entire U.S., all other site-specific parameters are user
supplied.
SWRRBWQ includes five major components: weather, hydrology, sedimentation,
nutrients, and pesticides. Processes considered include surface runoff,
return flow, percolation, evapotranspiration, transmission losses, pond
and reservoir storage, sedimentation, and crop growth. A weather generator
allows precipitation, temperature, and solar radiation to be simulated
when measured data is unavailable. The precipitation model is a first-order
Markov chain model, while air temperature and solar radiation are
generated from the normal distribution.
Sediment yield is based on the
Modified Universal Soil Loss Equation (MUSLE). Nutrient yields were
taken from the EPIC model (Williams et al., 1984). The pesticide component
is a modification of the CREAMS (Smith and Williams, 1980) pesticide model.
SWRRBWQ allows for simultaneous computations on each subbasin and routes
the water, sediment, nutrients, and pesticides from the subbasin outlets to
the basin outlet.
Surface runoff volume is predicted using the SCS curve number (USDA, 1972) as
a function of daily soil moisture content. Return flow is calculated as
a function of soil water content and return flow time. Return flow travel
times can be calculated from soil hydraulic properties or user-inputs.
The percolation component uses a storage routing model combined with a
crack-flow model to predict flow through the root zone. Evapotranspiration
is estimated using Ritchie's ET model. Transmission losses in the stream
channel are calculated as a function of channel dimensions, flow duration,
and effective hydraulic conductivity of the channel bed. Pond storage is
based on a water balance equation that accounts for inflow, outflow,
evaporation, and seepage. The reservoir water balance component is similar
to the pond component except that it allows flow from the principal and
emergency spillways.
Peak runoff rate predictions are based on a modification
of the Rational Formula. Sediment yield is computed for each subbasin
with the modified Universal Soil Loss Equation (MUSLE). The channel and
floodplain sediment routing model is composed of two components operating
simultaneously (deposition and degradation). Degradation is based on
Bagnold's stream power concept, and deposition is based on the fall velocity
of the sediment particles. Sediment is also routed through ponds and
reservoirs.
The crop growth model computes total biomass each day during
the growing season as a function of solar radiation and leaf area index (LAI).
LAI is computed for each day from the maximum LAI and total above ground biomass.
The ET component uses LAI to compute plant evaporation. Water and
temperature stress factors are used as growth constraints.
SWRRBWQ simulates crop growth for both annual and perennial plants. Annual
crops grow from planting date to harvest date or until the accumulated heat
units equal the potential heat units for the crop. Perennial crops
maintain their root systems throughout the year.
Lake water quality simulation can be applied when a single reservoir is
simulated at the basin outlet. The lake water quality computes the toxic
balance and the phosphorus mass balance in the lake, the equations for which
come from Chapra (1983) and from Thomann and Mueller (1987), respectively.
The major processes in the toxic balance are loading, outflow, reactions,
volatilization, settling, diffusion, resuspension, and burial, while in the
phosphorus balance, the balances are loading, outflow, and settling. The
model tracks the fate of pesticides from their initial applications on the
land to their final fate in the lake. This allows decision makers to directly
predict the influence of upland agricultural management decisions on lake
water quality.
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| File |
Size |
Download |
| SWRRBWQ User manaual for Windows 98/95/ME/XP/NT/2000 |
0.07MB |
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| SWRRBWQ User manaual (in PDF format) |
0.30MB |
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| SWRRBWQ model system for Windows 98/95/ME/XP/NT/2000 (Part 1/2) |
1.23MB |
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| SWRRBWQ model system for Windows 98/95/ME/XP/NT/2000 (Part 2/2) |
0.42MB |
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