SUMMARY OF GSFLOW


NOTE: Any use of trade, product, or firm names is for descriptive purposes
      only and does not imply endorsement by the U.S. Government.


ABSTRACT
     GSFLOW is a coupled Groundwater and Surface-water FLOW model
     based on the integration of the U.S. Geological Survey 
     Precipitation-Runoff Modeling System (PRMS, Leavesley and others, 1983) 
     and the U.S. Geological Survey Modular Groundwater Flow Model
     (MODFLOW-2005, Harbaugh, 2005). In addition to the basic PRMS and
     MODFLOW simulation methods, several additional simulation methods were 
     developed,and existing PRMS modules and MODFLOW packages were modified,
     to facilitate integration of the models. Methods were developed to route 
     flow among the PRMS Hydrologic Response Units (HRUs), between
     HRUs and the MODFLOW finite-difference cells, and between 
     HRUs and streams and lakes. PRMS and MODFLOW have similar modular
     programming methods, which allow for their integration while 
     retaining independence that permits substitution of and extension with 
     additional PRMS modules and MODFLOW packages. PRMS is implemented in 
     the U.S. Geological Survey Modular Modeling System (Leavesley and others,
     1996), which provides input and output and integration functions used by
     PRMS and GSFLOW modules.

     GSFLOW was developed to simulate coupled groundwater/surface-
     water flow in one or more watersheds by simultaneously simulating
     flow across the land surface, within subsurface saturated
     and unsaturated materials, and within streams and lakes. Climate
     data consisting of measured or estimated precipitation, air
     temperature, and solar radiation, as well as groundwater 
     stresses (such as withdrawals) and boundary conditions are the
     driving factors for a GSFLOW simulation. GSFLOW can be used to 
     evaluate the effects of such factors as land-use change, climate 
     variability, and groundwater withdrawals on surface and subsurface 
     flow. The model incorporates well documented methods for simulating 
     runoff and infiltration from precipitation; balancing energy and mass
     budgets of the plant canopy, snowpack, and soil zone; and simulating
     the interaction of surface water with ground water, in watersheds 
     that range from a few square kilometers to several thousand 
     square kilometers, and for time periods that range from months to
     several decades. An important aspect of GSFLOW is its ability
     to conserve water mass and to provide comprehensive water
     budgets.

     GSFLOW allows for three simulation modes--integrated, PRMS-only,
     and MODFLOW-only. The capability of having PRMS-only and 
     MODFLOW-only simulations in GSFLOW allows incremental model 
     setup that provides flexibility in model calibration.

     GSFLOW operates on a daily time step. In addition to the MODFLOW
     variable-length stress period used to specify changes in stress
     or boundary conditions, GSFLOW uses internal daily stress periods
     for adding recharge to the water table and calculating flows
     to streams and lakes. Only the first stress period specified in
     the MODFLOW input files can be designated as steady state for 
     integrated simulations. No computations pertaining to PRMS are 
     executed for an initial steady-state stress period.


HISTORY

      GSFLOW Version 1.1.6 03/20/2013 - This version of GSFLOW is based on 
         MODFLOW-2005 version 1.9.01, MODFLOW-NWT version 1.0.7, and PRMS 
         version 3.0.5. A number of enhancements and bug fixes have been done 
         for this release. All of the updates are described in file
         "GSFLOW_v1.1.6_Updates.pdf." 

      GSFLOW Version 1.1.5 01/15/2012 - This version of GSFLOW is based on 
         MODFLOW-2005 version 1.8, MODFLOW-NWT version 1.0.3 and PRMS version 
         3.4179. Several enhancements and bug fixes have been done for this 
         release. Important enhancements include addition of the Newton 
         Formulation for MODFLOW and the Map Results and Climate by HRU 
         Distribution Modules for PRMS. All of the updates are described in 
         the files "GSFLOW_v1.1.5_Updates.pdf," "Map_results.pdf," 
         "Climate_hru.pdf," "Appendix1_Tables_v1.1.5.pdf," and 
         "SFR2_for_GSFLOW_v1.1.5.pdf."

      GSFLOW Version 1.1.4 06/01/2011 - This version of GSFLOW is based 
         on MODFLOW-2005 version 1.8. Several bug fixes and relatively
         small modifications were made to a few of the PRMS modules 
         and MODFLOW Packages that are explained in the 'release.txt' file.

      GSFLOW Version 1.1.3 03/01/2011 - This version of GSFLOW is based 
         on MODFLOW-2005 version 1.8. This version of GSFLOW includes 
         (1) the new Grid Report Module, (2) enhanced input options for 
         the PRMS Parameter File, and (3) a new option for the SFR2 
         Package to specify streamflows to simulated stream segments in
         tabular files that are external to the SFR2 main input file. All 
         of the updates are described in the file 'GSFLOW_v1.1.3_Updates.pdf' 
         provided in the ./doc/GSFLOW subdirectory. Revised input 
         instructions for the SFR2 Package (for use with GSFLOW) are provided
         in file 'SFR2_for_GSFLOW_v1.1.3.pdf' in the same directory.

      GSFLOW Version 1.1.2 07/23/2010 - This version of GSFLOW is based 
         on MODFLOW-2005 version 1.8. Several bug fixes and relatively
         small modifications were made to a few of the GSFLOW modules 
         that are explained in the 'release.txt' file.
      
      GSFLOW Version 1.1.1 02/12/2010 - This version of GSFLOW is based 
         on MODFLOW-2005 version 1.8, which includes the Multi-Node Well
         version 2 Package. Additional modifications were made to 
         several GSFLOW modules that are explained in the 'release.txt'
         file.

      GSFLOW Version 1.1.00 11/18/2009 - This version of GSFLOW is based 
         on MODFLOW-2005 version 1.7. Added ability to specify inactive
         and swale hydrologic response unit types and the ability to 
         calculate streamflow at internal basin nodes (the latter for 
         PRMS-only simulations). Several additional bug fixes and minor
         enhancements were made for this release. All of the changes are
         described in the file 'GSFLOW_v1.1_Updates.pdf' located in the
         /doc/GSFLOW directory. Updated input formats for the PRMS and 
         GSFLOW modules, including several new input parameters, are provided 
         in the file 'Appendix1_Tables_v1.1.pdf,' which is also included in 
         the /doc/GSFLOW directory. Also made changes to the Sagehen sample
         problem by simplifying the MODFLOW Name File and making the MODFLOW
         transient stress period consistent with the total number of time
         steps simulated by GSFLOW; these changes did not affect the results
         of the sample problem.

      GSFLOW Version 1.0.00 03/05/2008 - Initial release.


SYSTEM REQUIREMENTS
     GSFLOW is written in Fortran 90 and C programming languages.
     The code has been used on personal computers running various
     forms of the Microsoft Windows operating system and LINUX
     based computers.


FUNTIONALITY
     This version of GSFLOW includes the following PRMS and GSFLOW 
     modules, MODFLOW-NWT and MODFLOW-2005 packages, and Modular 
     Modeling System routines:
    
     PRMS modules:
         basin         -- Basin Module
         cascade       -- Cascading-Flow Module
         obs           -- Observed-Data Module
         soltab        -- Potential Solar-Radiation Module
         temp_1sta     -- One-Station Temperature-Distribution Module
         temp_laps     -- Lapse-Station Temperature-Distribution Module
         temp_dist2    -- Inverse-Distance Temperature-Distribution Module
         xyz_dist      -- Multiple Linear Regression Precipitation- and 
                               Temperature-Distribution Module
         precip_1sta   -- One-Station Precipitation-Distribution Module
         precip_laps   -- Lapse-Station Precipitation-Distribution Module
         precip_dist2  -- Inverse-Distance Precipitation-Distribution 
                               Module
         ddsolrad      -- Degree-Day Solar-Radiation Distribution Module
         ccsolrad      -- Cloud-Cover Solar-Radiation Distribution Module
         potet_jh      -- Jensen-Haise Potential-Evapotranspiration Module
         potet_hamon   -- Hamon Potential-Evapotranspiration Module       
         potet_pan     -- Pan-Evaporation Potential-Evapotranspiration
                               Module
         transp_tindex -- Active Transpiration Period Module
         intcp         -- Precipitation-Interception Module
         snowcomp      -- Snow Module
         srunoff_smidx -- Nonlinear Source Area Surface-Runoff and
                               Infiltration Module
         srunoff_carea -- Linear Source Area Surface-Runoff and 
                               Infiltration Module
         soilzone      -- Soil-Zone Module
         gwflow        -- Groundwater Reservoir Module (for PRMS-only 
                               simulations)
         subbasin      -- Subbasin Module (for PRMS-only simulations)
         strmflow      -- Streamflow Module (for PRMS-only simulations)
         basin_sum     -- Watershed Flow-Summary Module (for PRMS-only                    
                               simulations)
         map_results   -- Map Results Module (for PRMS-only simulations)
         climate_hru   -- Climate by HRU Distribution Module


     MODFLOW-NWT and MODFLOW-2005 packages (and OBS Process):
       
         BAS -- Basic Package
         BCF -- Block-Centered Flow Package
         LPF -- Layer-Property Flow Package
         HUF -- Hydrogeologic-Unit Flow Package
         HFB -- Horizontal Flow Barrier Package
         CHD -- Time-Variant Specified-Head Option
         WEL -- Well Package
         MNW1 -- Multi-Node Well Package, version 1
         MNW2 -- Multi-Node Well Package, version 2
         GHB -- General Head Boundary Package
         FHB -- Flow and Head Boundary Package
         SFR -- Streamflow-Routing Package
         LAK -- Lake Package
         UZF -- Unsaturated-Zone Package
         GAG -- Gage Package
         NWT -- Newton Solver Package
         UPW -- Upstream-Weighting Package
         SIP -- Strongly Implicit Procedure Package
         PCG -- Preconditioned Conjugate Gradient Package
         DE4 -- Direct solver
         GMG -- Geometric MultiGrid Solver Package
         PCGN -- Preconditioned Conjugate Gradient Package with improved 
                  nonlinear control Package


     GSFLOW modules:
         gsflow_prms    -- Computational-Sequence Control for PRMS and GSFLOW 
                            Module
         gsflow_modflow -- Computational-Sequence Control for MODFLOW Module
         gsflow_setconv -- Unit-Conversions Module
         gsflow_prms2mf -- PRMS to MODFLOW Integration Module
         gsflow_mf2prms -- MODFLOW to PRMS Integration Module
         gsflow_budget  -- Watershed-Budget Summary Module
         gsflow_sum     -- Flow-Components Summary Module


     Modular Modeling system (MMS) routines:
         gsflow_main    -- Main Program to Manage PRMS Modules and 
                            MODFLOW-2005 Packages
         mms_util       -- MMS Utility Routines


DOCUMENTATION

Markstrom, S.L., Niswonger, R.G., Regan, R.S., Prudic, D.E., and
Barlow, P.M., 2008, GSFLOW--Coupled Ground-water and Surface-water
FLOW model based on the integration of the Precipitation-Runoff
Modeling System (PRMS) and the Modular Ground-Water Flow Model
(MODFLOW-2005): U.S. Geological Survey Techniques and Methods
6-D1, 240 p.


REFERENCES

Harbaugh, A.W., 2005, MODFLOW-2005, the U.S. Geological Survey
modular ground-water model--the Ground-Water Flow Process: U.S.
Geological Survey Techniques and Methods 6-A16, variously
paginated.

Leavesley, G.H., Lichty, R.W, Troutman, B.M., and Saindon,
L.G., 1983, Precipitation-runoff modeling system--User's
manual: U.S. Geological Survey Water-Resources Investigations
Report 83-4238, 207 p.

Leavesley, G.H., Restrepo, P.J., Markstrom, S.L., Dixon, M.,
and Stannard, L.G., 1996, The Modular Modeling System (MMS):
User's manual: U.S. Geological Survey Open-File Report 96-151,
142 p.


CONTACTS
    U.S. Geological Survey
    Office of Ground Water
    411 National Center
    Reston, VA 20192
    (703) 648-5001
    ogw_webmaster@usgs.gov
