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.