SWRRBWQ (Simulator for Water Resources in Rural Basins - Water
   Quality) was developed for simulating hydrologic and related
   processes in rural basins (Arnold et al., 1990; Williams et al.,
   1985).  The objectives of the model are to predict the effect of
   management decisions on water, sediment, nutrient, and pesticide
   yields with reasonable accuracy for ungaged rural basins throughout
   the U.S.  To satisfy these objectives, the model is: (a) physically
   based and uses readily available inputs (calibration is not
   possible on ungaged basins); (b) capable of computing the effects
   of management changes on outputs; (c) computationally efficient to
   allow simulation on a variety of management strategies without
   excessive cost; (d) capable of simulating long periods for use in
   frequency analysis; and (e) capable of operating on subdivided
   basins (soils, land use, management, etc., make subdivision
   necessary).  

   SWRRBWQ was developed from SWRRB by adding the CREAMS (Knisel,
   1980) pesticide components.  The CREAMS daily rainfall hydrology
   model was modified to create SWRRB for application to large,
   complex, rural basins.  The major changes involved were: (a) the
   model was expanded to allow simultaneous computations on several
   subbasins to predict the basin water yield; (b) a return flow
   component was added; (c) a reservoir storage component was added
   for use in determining the effects of farm ponds on other
   reservoirs on water yield; (d) a weather simulation model
   (rainfall, solar radiation, and temperature) was added to provide
   for longer term simulations and more representative weather inputs,
   both temporally and spatially; (e) a better method was developed
   for predicting the peak runoff rate; (f) a crop growth model was
   added to account for annual variation in growth; (g) a simple flood
   routing component was added; (h) components were added to simulate
   sediment through ponds, reservoirs, streams, and valleys; and (i)
   transmission losses were calculated.  Besides water, SWRRB also
   simulates sediment yield from rural basins using the Modified
   Universal Soil Loss Equation (MUSLE) and a sediment routing model. 
   Subbasins nutrient yield and nutrient cycling were taken from the
   EPIC model (Williams et al. 1984) and modified as necessary for
   inclusion into the SWRRB model.  SWRRB allows for simultaneous
   computations on each subbasin and routes the water, sediment, and
   nutrients from the subbasin outlets to the basin outlet. 
   ___________________________________________________________________

   Arnold, J.G., J.R. Williams, A.D. Nicks, and N.B. Sammons. 1990.
     SWRRB: A Basin Scale Simulation Model for Soil and Water
     Resources Management. Texas A&M Press. 255 pp.
 
   Arnold, J.G., J.R. Williams, R.H. Griggs, and N.B. Sammons. 1991.
     SWRRBWQ: A Basin Scale Model for Assessing Management Impacts on
     Water Quality.  USDA-ARS, Grassland, Soil and Water Research
     Laboratory, Temple, TX, 76502. Unpublished report.

   Knisel, W.G.  (ed.), 1980.  CREAMS:  A Field-scale Model for
     Chemicals, Runoff, and Erosion from Agricultural Management
     Systems, U.S. Department of Agriculture, Science and Education
     Administration, Conservation  Research Report 26, 643 pages.  
     USDA, 1984.
  
   Williams, J.R., C.A. Jones, and P.T. Dyke. 1984. A modeling
     approach to determining the relationship between erosion and soil
     productivity.  Trans. ASAE 27:129-144.

   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.