U.S. Geological Survey
Water Resources Applications Software

Geochemical || Ground Water || Surface Water || General

Summary of MF2K-GWT

The Ground-Water Transport (GWT) Package for MODFLOW-2000 (mf2k) provides the
capability to simulate three-dimensional solute transport.  The GWT Package is 
based on the previously documented MOC3D model, which was integrated with 

MODFLOW-96.  Version 1.0 of the GWT Package was constructed by merging version 

3.5 of MOC3D with Version 1.1 of mf2k and adding solute calculations compatible
with the new Lake and Gage Packages.  The original MOC3D Package was documented 

  Konikow, L.F., Goode, D.J., and Hornberger, G.Z., 1996, A three-
    dimensional method-of-characteristics solute-transport model
    (MOC3D): U.S. Geological Survey Water-Resources Investigations
    Report 96-4267, 87 p.

Additions and modifications to the GWT
package are documented in:

  Kipp, K.L., Jr., Konikow, L.F., and Hornberger, G.Z., 1998, An
    implicit dispersive transport algorithm for the U.S. Geological
    Survey MOC3D solute-transport model: U.S. Geological Survey
    Water-Resources Investigations Report 98-4234, 54 p.

  Goode, D.J., 1999, Age, double porosity, and simple reaction
    modifications for the MOC3D ground-water transport model:  U.S.
    Geological Survey Water-Resources Investigations Report 99-4041,
    34 p.

  Heberton, C.I., Russell, T.F., Konikow, L.F., Hornberger, 
    G.Z., 2000, A three-dimensional finite volume Eulerian-
    Lagrangian Localized Adjoint Method (ELLAM) for solute-
    transport modeling: U.S. Geological Survey Water-Resources 
    Investigations Report 00-4087, 63 p.

  Merritt, M.L., and Konikow, L.F., 2000, Documentation of a computer 
    program to simulate lake-aquifer interaction using the MODFLOW 
    ground-water flow model and the MOC3D solute-transport model: U.S. 
    Geological Survey Water-Resources Investigations Report 00-4167, 
    146 p.

  Hornberger, G.Z., Konikow, L.F., and Harte, P.T., 2002, Simulating 
    horizontal-flow barriers using the MODFLOW Ground-Water Transport 
    Process: U.S. Geological Survey Open-File Report 02-52, 28 p. 

  Konikow, L.F., and Hornberger, G.Z., 2003, Use of boundary fluxes 
    when simulating solute transport with the MODFLOW Ground-Water 
    Transport Process: U.S. Geological Survey Open-File Report 
    03-303, 17 p. 
Konikow, L.F., and Hornberger, G.Z., 2006, Use of Multi-Node Well
(MNW) Package when simulating solute transport with the MODFLOW
Ground-Water Transport Process: U.S. Geological Survey Techniques
and Methods 6-A15, 34 p.

Winston, R.B., Konikow, L.F., and Hornberger, G.Z., 2018, Volume-
weighted particle-tracking method for solute- transport modeling;
Implementation in MODFLOW–GWT: U.S. Geological Survey Techniques
and Methods, book 6, chap. A58, 44 p., https://doi.org/10.3133/tm6A58.

  Version 1.10 3/13/2018 Compatible with MF2K 1.18. Added support for 
explicit (MOCWT) and implicit (MOCWTI) volume-weighted particle-
tracking method for solute-transport modeling. Includes MNW2 package.

Version 1.9.8 10/22/2008 Fixed SFR array initialization. BFLX with
variable grid spacing bug fix. Ellam bug with Lakes and/or MNWs fixed.
  Version 1.9.7 7/10/2007 Fixed lake array pointer bug.  Initialized
solute-routing arrays.
  Version 1.9.6 5/16/2007 Fixed calculation of concentration entering
lakes from streams. Corrected budget report of mass entering from
subgrid boundary. Fixed memory leak in MNW simulations.
  Version 1.9.5 5/2/2007 Lake concentration updated for case of lake 
with inflow tributaries only. Fixed index for CHFB calculation.
Changed CHFB allocation.

Version 1.9.4 4/20/2007 Fixed error in computing stream (SFR) outflow.

Version 1.9.3 3/28/2007 Compatible with MF2K 1.17.02.

Version 1.9.2 11/13/2006 Fixed SRF2 bug to allow ISFROPT=1.

Version 1.9.1 11/9/2006 - Compatible with MF2K 1.17.01. Bug in
routing solute in MNWs fixed. ET option 3 now compatible. Fixed
memory deallocation error when using PTOB package. Changed algorithm
for creating particles at subgrid boundaries. Velocity output for
ELLAM with RF>1 fixed. CBDY package fixed for no lateral subgrid.

Version 1.9 4/14/2006 - Compatible with MF2K 1.16, including GMG
solver. Compatibility of AGE package with ELLAM solver added.
Compatibility with MNW package added (see Konikow and Hornberger,
2006), including MNWO package for concentration output at MNWs.
The dispersion algorithm was altered to more accurately restrict
the dispersive transfer of mass so as not to exceed the available
mass in the cell. The mass-balance residual calculation now includes
a check for precision in the case where the change in mass stored is
negligible. When AGE and ET are used together, evapotranspirtation
does not concentrate age mass as it does for a solute; age mass is
removed from the system with the fluid sink.

Several new packages added, see input instructions document
(GWT_Input_Instructions.pdf) for details on implementation.

CBDY: specify spatially varying source concentrations in flow
across subgrid boundaries.

SSTR: specify that transient transport calculations will begin
after the first stress period of the flow simulation.

PRTP: indicate that z-location of printed particle locations
will be adjusted for changes in water-table elevation
relative to cell dimensions.

Bug fixes: The mass balance item for DRT uses the average
concentration. The NCHNDS parameter is now read and used correctly
in the BFLX package. CRCH for NRCHOP>1 now works. Several bugs
in ELLAM fixed. In ELLAM the SSLUGM solver has been replaced with
the SSDGMR (diagonally scaled) solver. Several arrays now correctly
deallocated. Binary velocities are printed correctly. Leon Kauffman
was instrumental in locating and fixing several bugs for this release.

Version 1.8.1 11/29/2004 - Removed extraneous adjustment for
z-direction dispersion calculation. Reset SMALL (a check for loss
of precision) to 1E-4. NL array redimensioned in ELLAM. Fixed SFR
segments with concentrations associated with external sources.

Version 1.8 7/6/2004 - Compatible with MF2K 1.14, including SFR
package. Fixed bug in dispersion routines for both explicit and
implicit methods. IGENLK initialized when LAK package inactive.
Fixed bug for transient flow conditions with ELLAM method.

Version 1.7 9/23/2003 - Compatible with MF2K-1.12. Fixed bug
related to CHD package.

Version 1.6 9/3/2003 - Compatible with MF2K 1.11. Added BFLX
package, including rearrangement and splitting of velocity sub-
routines. Cross-product dispersion terms for explicit and implicit
methods fixed for cases with variable cell thickness. Source term
fixed for implicit method. CHFB statements merged into normal dis-
persion subroutines. Losing lake cells treated as strong sources.
Half-life printed to output file. Changed sign of change in mass
stored budget item (now positive is increase in mass stored).
  Version 1.5 11/14/2002 -  For implicit method, fixed mass balance 
errors associated with dispersion terms in z-direction by
accounting for different thickness in layer K+1. Corrected layer-
index calculation for CINFL (C' at subgrid boundary) for certain
  Version 1.4 8/1/2002 - Compatible with MODFLOW-2000 version 1.10.  
Revised GAGE Package for lakes to allow more comprehensive output.
Fixed mass balance errors associated with dispersion terms in
z-direction by accounting for different thickness in layer K+1.
Improved roundoff error check in particle moving routine.
Improved algorithm for replacing particles at subgrid boundaries.
Added automatic update of saturated thickness for simulation of
unconfined aquifer with multiple steady-state stress periods.
  Version 1.3 2002/5 - Compatible with MODFLOW-2000 1.8.
  Version 1.21 2002/3 - Saturated thickness of cells in unconfined 
layers is recomputed for new steady-state stress periods. This may
cause a 'jump' in solute mass at the transition from one stress
period to the next.
  Version 1.2 2002/2 - Compatibilty with CHD Package. 
  Version 1.1 2002/2 - CHFB Package added.  Minor corrections 
and improvements to GWT main output file and OBS file.
  Version 1.0.8 2001/12 - Compatible with MODFLOW-2000 1.7. 
  Version 1.0.7 2001/11 - Compatible with MODFLOW-2000 1.6. 
DATA and DATA(BINARY) files can be designated as input or output
files (using "OLD" and "REPLACE" specifications as described in
MODFLOW-2000 Release Notes for Version 1.6.
  Version 1.0.6 2001/08 - Compatible with MODFLOW-2000 1.5. 
Fixed bug relating to particles near subgrid boundary.
  Version 1.0.5 2001/07 - Compatible with MODFLOW-2000 1.4.
  Version 1.0.4 2001/06 - Added compatibility with DRT package.  
When drain return flow is used, the concentration of the
drain "donor" cell is used for the concentration of the
return flow.
  Version 1.0.3 2001/05 - Update to produce unformatted unstructured
"binary" files (see MODFLOW-2000 1.2 update)
  Version 1.0.2 2001/04 - FHB and HFB bug fix (swapped unit numbers)
  Version 1.0.1 2001/02 - Fix for thickness calculation in unconfined layers; 
fixed binary output for concentration
  Version 1.0 2001/01 - Initial release