1. General Model Information

Name: Simulator for Water Resources in Rural Basins-Water Quality

Acronym: SWRRBWQ

Main medium: terrestrial
Main subject: hydrology, biogeochemistry
Organization level: landscape
Type of model: not specified, Markov chain
Main application:
Keywords: watershed, sedimentation, erosion, nutrient, pesticide, transport, management effect, basin scale, continuous-time, spatially distributed, capacity cascade soil water model, crack flow, ritchie actual evapotranspiration, curve-number-runoff, windows-interface, soil database


Jeff Arnold
USDA ARS, Temple, TX
email: arnold@brc.tamus.edu


Arnold, J.G., J.R. Williams, R.H. Griggs, and N. B. Sammons. 1990


SWRRBWQ was developed to simulate 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.

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 (Arnold et al., 1991).

SWRRBWQ has been equipped with a Windows-Interface including help screens, which makes editing of input files (in spreadsheet-format) user friendly.

II. Technical Information

II.1 Executables:

Operating System(s): Following SWRRBWQ model files (program and user manaual) are downloadable for Microsoft Windows. The minimum system requirements are provided below:

II.2 Source-code:

Programming Language(s):

II.3 Manuals:

(see Executables)

II.4 Data:

III. Mathematical Information

III.1 Mathematics

III.2 Quantities

III.2.1 Input

III.2.2 Output

IV. References

Arnold, J.G., J.R. Williams, R.H. Griggs, and N. B. Sammons. 1991. SWRRBWQ - A Basin Model for Assessing Management Impacts on Water Quality. Draft. USDA. ARS, Grassland, Soil, and Water Research Laboratory, Temple, TX.
Arnold, J.G., J.R. Williams, R.H. Griggs, and N. B. Sammons. 1990. SWRRB - A Basin Scale Simulation Model for Soil and Water Resources Management. Texas A & M Press.
Arnold, J. G. and N. B. Sammons. 1988. Decision Support system for selecting inputs to a basin scale model. Water Resources Bull. 24(4):749-759.
Arnold, J. G.. and J. R. Williams. 1987. Validation of SWRRB - Simulator of Waters in rural basins. J. Water Resources Planning and Management. ASCE 113(2):243-246.
Chapra, S. C. 1979. Water-related fate of 129 priority pollutants. USEPA-440/4-79-029B.
Chapra, S. C. and S. J. Tarpchak. 1976. A chlorophyll a model and its relationship to phosphorus loading plots for lakes. Water Resources Res. 12(6)0:1260-1264.
Nicks, A. B., C. W. Richardson, and J. R. Williams. 1990. Evaluation of the EPIC Model Weather Generator. EPIC - Erosion/Productivity Impact Calculator Model Document. USDA. ARS. Technical Bulletin Number 1768: 105-124.
Thomann, R. V. and J. A. Mueller. 1987. Principles of Surface Water Modeling and Control. Harper and Row, Inc., New York.
Williams, J. R., A. D. Nicks, and J. G. Arnold. 1985. Simulator for Water Resources in rural basins. J. Hydr. Eng., ASCE 111(6):970-986.

V. Further information in the World-Wide-Web

  • SWRRBWQ at the US-EPA Environmental/Water Resources Computer Model Library in the Department of Civil and Environmental Engineering, ODU
  • SWRRBWQ Fact Sheet for Hydrologic Unit Water Quality HU/WQ or HUWQ
    Simulator for Water Resources in Rural Basins-Water Quality (SWRRBWQ) pollutant loading model. NRCS-Version 3210SCS94a. Developer, National Model Leader,..
  • Environmental/Water Resources Computer Model Library in the Department of Civil and Environmental Engineering, ODU
  • Water, Field Scale Computer Models
    Water, Field Scale and Watershed Scale Computer Models, Field and/or Point Assessment Tools, and Tools Under Developement. 1. Agricultural Non-Point...
  • Simulator for Water Resources in Rural Basins-Water Quality
    U.S. Department of Agriculture, Agricultural Research Service, and Texas Agricultural Experiment Station, Temple, Texas, and the National Soil Erosion...

    VI. Additional remarks

    SWRRB was developed by modifying the CREAMS daily rainfall model for large, complex basins. Major additions to the CREAMS models include allowing simultaneous computations for severalsubwatersheds within a large basin and adding components to simulateweather, return flow, pond and reservoir storage, crop growth,transmission losses, groundwater, and sediment routing. SWRRBoperates on a daily time step and is capable of simulations upto 100 years or more. SWRRB allows basins to be divided according to landuse,soils, and topography. Since SWRRB places a limit on the numberof subbasins within a watershed, some lumping of input parametersis necessary. Several of the modules of SWRRB have been used or modified within the GIS-based large scale models
    Last review of this document by: T. Gabele: 08. 07. 1997, J. Bierwirth 05.10.2000 -
    Status of the document:
    last modified by Tobias Gabele Thu Jul 15 02:07:22 CEST 2004

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