Summary of GWM-2005
ABSTRACT
GWM-2005 is a Groundwater Management Process for the U.S. Geological Survey
modular three-dimensional groundwater model, MODFLOW-2005. GWM-2005 uses a
response-matrix approach to solve several types of linear, nonlinear, and
mixed-binary linear groundwater management formulations. Each management
formulation consists of a set of decision variables, an objective function, and
a set of constraints. Three types of decision variables are supported by
GWM-2005: flow-rate decision variables, which are withdrawal or injection
rates at well sites; external decision variables, which are sources or sinks of
water that are external to the flow model and do not directly affect the state
variables of the simulated groundwater system (heads, streamflows, and so
forth); and binary variables, which have values of 0 or 1 and are used to define
the status of flow-rate or external decision variables. Flow-rate decision
variables can represent wells that extend over one or more model cells and be
active during one or more model stress periods; external variables also can be
active during one or more stress periods. A single objective function is
supported by GWM-2005, which can be specified to either minimize or maximize
the weighted sum of the three types of decision variables. Four types of
constraints can be specified in a GWM-2005 formulation: upper and lower bounds
on the flow-rate and external decision variables; linear summations of the three
types of decision variables; hydraulic-head based constraints, including
drawdowns, head differences, and head gradients; and streamflow and
streamflow-depletion constraints.
The Response Matrix Solution (RMS) Package of GWM-2005 uses the Groundwater
Flow Process of MODFLOW to calculate the change in head at each constraint
location that results from a perturbation of a flow-rate variable; these changes
are used to calculate the response coefficients. For linear management
formulations, the resulting matrix of response coefficients is then combined
with other components of the linear management formulation to form a complete
linear formulation; the formulation is then solved by use of the simplex
algorithm, which is incorporated into the RMS Package. Nonlinear formulations
arise for simulated conditions that include water-table (unconfined) aquifers or
head-dependent boundary conditions (such as streams, drains, or
evapotranspiration from the water table). Nonlinear formulations are solved by
sequential linear programming; that is, repeated linearization of the nonlinear
features of the management problem. In this approach, response coefficients are
recalculated for each iteration of the solution process. Mixed-binary linear (or
mildly nonlinear) formulations are solved by use of the branch and bound
algorithm, which is also incorporated into the RMS Package.
HISTORY
Version 1.5.0; 2012/09 - Added capability to use MNW-type wells as decision
variables (Ahlfeld and Barlow, 2013). Head constraints and state variables also
can be specified for MNW-type wells. Added version 2.0 of MODFLOW-LGR. Minor output
and code improvements.
Version 1.4.2; 2013/03 - Add options for stream leakage constraints and stream
leakage state variables. Minor output improvment.
Version 1.4.1; 2012/6 - Corrected bug that limits the number of coefficients that
can be applied to a state variable. Executable compiled with 'maximize speed'
option.
Version 1.4.0; 2012/4 - Added capability for drain state variables that can
be used to define flow or volume over time at multiple drain cells (see file
'Drains.pdf' in the doc subdirectory). Also added a current, complete set of
input instructions for files used by GWM-2005. See file
'Input_instructions_v1.4.0.pdf' in the doc subdirectory.
Version 1.3.1; 2011/5 - Correct several output bugs and bugs affecting binary
variables. Add state variable output status feature and new solution type to
perform forward run, evaluate constraints and stop.
Version 1.3.0; 2011/3 - Update GWM-2005 with State Variables Package (Ahlfeld and
others,2011). Also made small adjustments to the format of the GWM output file.
Version 1.2.02 2010/7 - Update GWM-2005 with most recent version of MODFLOW-LGR
(version 1.2).
Version 1.2.01 2010/1 - Bug corrected that caused GWM to fail when IBASE set to
one in the SOLN input file. This bug only occurs in Version 1.2 of GWM-2005.
Implement minor improvements and corrections to output.
Version 1.2 2009/12 - Added capability to accommodate problems on multiple grids
using MODFLOW-LGR. Reconstructed from MODFLOW-LGR version 1.1.02. Added CRITMFC
input parameter to control flow process closure criteria. Changed name of program
from MF2005-GWM to GWM-2005. Published new documentation report
(Ahlfeld and others, 2009).
Version 1.1 2009/06 - Reconstructed from MODFLOW-2005 Version 1.6.02. Added
capability for placement of streamflow constraints when SFR package is used. Bug fix
that caused code failure when equality summation constraints were imposed on binary
variables. Bug fix to correct output for SLP runs. See release.txt for more details.
Version 1.0.1 2008/08 - Reconstructed from MODFLOW-2005 Version 1.5.00. Bug fix
that prevented use of LPF or HUF packages. Change to output to GWMWFILE so that
well information is printed even when stress is zero. New feature to allow
formatted output of response matrix under NS option. See 'release.txt' for
details.
Version 1.0.0 2007/07/12 - Initial release, built from MODFLOW-2005 Version
1.3.01 and MF2K-GWM Version 1.1.1
PROCESSES
This version of GWM-2005 includes the following processes:
GWF2 -- Groundwater Flow Process
GWM1 -- Groundwater Management Process
OBS2 -- Observation Process
PACKAGES
In addition to all of the packages included with Version 2.0 of MODFLOW-LGR
(based on Version 1.8 of MODFLOW-2005) this version of GWM-2005 includes
the following packages:
DCV3 -- Decision Variable Package
OBJ3 -- Objective Function Package
HDC3 -- Head Constraints Package
STA3 -- State Variable Package
STC3 -- StreamFlow Constraints Package
SMC3 -- Summation Constraints Package
DCC3 -- Decision-Variable Constraints Package
RMS3 -- Response Matrix Solution Package
BAS3-GWM -- Basic Package for GWM
DOCUMENTATION
Ahlfeld, D.P., Baker, K.M., and Barlow, P.M., 2009, GWM-2005--A Groundwater-
Management Process for MODFLOW-2005 with Local Grid Refinement (LGR)
capability: U.S. Geological Survey Techniques and Methods, 6-A33, 65 p.
Ahlfeld, D.P., and Barlow, P.M., 2013, Use of multi-node wells in the Ground-
water-Management Process of MODFLOW-2005 (GWM-2005): U.S. Geological Survey
Techniques and Methods, 6-A47, 26 p.
Ahlfeld, D.P., Barlow, P.M., and Baker, K.M., 2011, Documentation for the
State Variables Package for the Groundwater-Management Process of
MODFLOW-2005 (GWM-2005): U.S. Geological Survey Techniques and Methods,
6-A36, 45 p.
Ahlfeld, D.P., Barlow, P.M., and Mulligan, A.E., 2005, GWM--A ground-water
management process for the U.S. Geological Survey modular ground-water
model (MODFLOW-2000): U.S. Geological Survey Open-File Report 2005-1072,
124 p.