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Techniques and Methods 6–A33

Groundwater Resources Program

GWM-2005—A Groundwater-Management Process for MODFLOW-2005 with Local Grid Refinement (LGR) Capability

By David P. Ahlfeld1, Kristine M. Baker1, and Paul M. Barlow2

1 University of Massachusetts.
2 U.S. Geological Survey.

ABSTRACT

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This report describes the Groundwater-Management (GWM) Process for MODFLOW-2005, the 2005 version of the U.S. Geological Survey modular three-dimensional groundwater model. GWM can solve a broad range of groundwater-management problems by combined use of simulation- and optimization-modeling techniques. These problems include limiting groundwater-level declines or streamflow depletions, managing groundwater withdrawals, and conjunctively using groundwater and surface-water resources. GWM was initially released for the 2000 version of MODFLOW.

Several modifications and enhancements have been made to GWM since its initial release to increase the scope of the program’s capabilities and to improve its operation and reporting of results. The new code, which is called GWM-2005, also was designed to support the local grid refinement capability of MODFLOW-2005. Local grid refinement allows for the simulation of one or more higher resolution local grids (referred to as child models) within a coarser grid parent model. Local grid refinement is often needed to improve simulation accuracy in regions where hydraulic gradients change substantially over short distances or in areas requiring detailed representation of aquifer heterogeneity. GWM-2005 can be used to formulate and solve groundwater-management problems that include components in both parent and child models. Although local grid refinement increases simulation accuracy, it can also substantially increase simulation run times.

First posted November 2009

For additional information contact:
U.S. Geological Survey
Office of Groundwater
411 Federal Center
Reston, VA 20192
(703)642-5001

http://water.usgs.gov/ogw/

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Suggested citation:

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.



Contents

Preface

Abstract

Introduction

Purpose, Scope, and Terminology

Groundwater-Management (GWM) Process for MODFLOW

Local Grid Refinement Capability of MODFLOW-2005

New Features in GWM

Enhanced Options for Reading and Writing Response-Coefficient Matrixes

Change to Solution Variable NPGNMX: Turning Off Reexecution of the GWF Process

Writing of Flow-Rate Decision Variables in the Optimal Solution to a MODFLOW Well-Type File

Use of the GWM OUT File in Place of the GLOBAL File

Specification of Streamflow Constraints with the Streamflow-Routing (SFR) Package

Option to Adjust the Closure Criteria for GWF Process Runs

GWM-2005 with Local Grid Refinement

Formulation of Groundwater-Management Problems with Both Parent and Child Models

Decision Variables

Objective Function

Constraints

Integration of LGR into the GWM Process

GWM Solution Algorithms for Management Problems with Both Parent and Child Models

GWM Output for Multiple Models

Input Instructions and Output Files

MODFLOW NAME File

MODFLOW DISCRETIZATION File

Considerations for Preparing MODFLOW-2005 Files for Use with LGR

LGR CONTROL File

GWM Process Files

GWM File

Decision Variable (DECVAR) File

Objective Function (OBJFNC) File

Constraint Files

Decision-Variable Constraints (VARCON) File

Linear-Summation Constraints (SUMCON) File

Head Constraints (HEDCON) File

Streamflow Constraints (STRMCON) File

Solution and Output-Control Parameters (SOLN) File

Output Files

Sample Problems

Changes to Original Sample Problems

SUPPLY2 Sample Problem with Streamflow-Routing (SFR) Package

DEWATER-LGR

Linear Groundwater-Management Formulation

Selected Input and Output Files for Sample Problem

SEAWATER-LGR

Mixed-Binary Nonlinear Groundwater-Management Formulation

Sensitivity Analysis of Convergence Criteria

Selected Input and Output Files for Sample Problem

SUPPLY-3GRID

Mixed-Binary Linear Groundwater-Management Formulation

Selected Input Files for Sample Problem

Acknowledgments

References Cited

Appendix: Program Modifications to Convert GWM-2000 to GWM-2005



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