Harbaugh, A.W.

e-mail: harbaugh@srv1rvares.er.usgs.gov

MODFLOW is a 3D, cell-centered, finite difference, saturated flow model developed by the United States Geological Survey (McDonald & Harbaugh, 1988). MODFLOW can perform both steady state and transient analyses and has a wide variety of boundary conditions and input options.

MODFLOW is divided into a series of components called "packages." Each package performs a specific task. Some of the packages are always required for a simulation and some are optional. The input for each package is contained in a separate text file.

**Basic Package (BAS1)**

The basic package is always required. The input to the basic package includes the grid dimensions, the computational time steps, and an array identifying which packages are to be used.**Output Control (OUT1)**

The output control file controls what information is to be output from MODFLOW and when it is to be output.**Block Centered Flow Package, Version 1 (BCF1)**

The block centered flow package performs the cell by cell flow calculations. The input to this package includes layer types and cell attributes such as storage coefficients and transmissivity.**Block Centered Flow Package, Version 2 (BCF2)**

The BCF2 package is similar to BCF1 except that the capability to rewet dry cells has been added.**Block Centered Flow Package, Version 3 (BCF3)**

The BCF3 package is similar to BCF2 except that a more sophisticated technique for computing cell to cell conductances is supported.**River Package (RIV1)**

The river package is used to simulate river type boundary conditions.**Recharge Package (RCH1)**

The recharge package is used to simulate recharge to the groundwater from precipitation.**Well Package (WEL1)**

The well package is used to simulate well type boundary conditions.**Drain Package (DRN1)**

The drain package is used to simulate drain type boundary conditions.**Evapotranspiration Package (EVT1)**

The evapotranspiration package is used to simulate the effect of evapotranspiration in the vadose zone.**General Head Package (GHB1)**

The general head boundary package is used to simulate head type boundary conditions where the value of the boundary condition depends on the head in the cell. Commonly used to simulate lakes.**Strongly Implicit Procedure Package (SIP1)**

The SIP package is an iterative solver based on the strongly implicit procedure.**Pre- conditioned Conjugate Gradient Package, Version 2 (PCG2)**

The PCG2 package is an iterative solver based on the preconditioned conjugate gradient technique.**Slice Successive Over-relaxation Package (SOR1)**

The SSOR package is an iterative solver based on the slice successive overrelaxation technique.

- The basic model is documented in:

**McDonald, M.G. and Harbaugh, A.W., 1988,**A modular three-dimensional finite-difference ground-water flow model: U.S. Geological Survey Techniques of Water-Resources Investigations Book 6, Chapter A1, 586p.- The PCG2 Package is documented in:

**Hill, M.C., 1990,**Preconditioned conjugate-gradient 2 (PCG2), a computer program for solving ground-water flow equations: U.S. Geological Survey Water-Resources Investigations Report 90-4048, 43 p.- The STR1 Package is documented in:

**Prudic, D.E., 1989,**Documentation of a computer program to simulate stream-aquifer relations using a modular, finite-difference, ground-water flow model: U.S. Geological Survey Open-File Report 88-729, 113 p.- The IBS1 and CHD1 Packages are documented in:

**Leake, S.A. and Prudic, D.E., 1988,**Documentation of a computer program to simulate aquifer-system compaction using the modular finite-difference ground-water flow model: U.S. Geological Survey Open-File Report 88-482, 80 p.- The GFD1 Package is documented in:

**Harbaugh, A.W., 1992,**A generalized finite-difference formulation for the U.S. Geological Survey modular three-dimensional finite-difference ground-water flow model: U.S. Geological Survey Open-File Report 91-494, 60 p.- The BCF3 Package is documented in 3 pieces. It builds on two previous versions of the Block-Centered Flow (BCF) Package. Documentation for the BCF1 Package describes the fundamental function of all BCF Packages. This documentation is contained in the basic model documentation (TWRI 6-A1 above).

BCF2 documentation describes the addition of the capability to convert dry cells to wet:

**McDonald, M.G., Harbaugh, A.W., Orr, B.R., and Ackerman, D.J., 1992,**A method of converting no-flow cells to variable-head cells for the U.S. Geological Survey modular finite-difference ground-water flow model: U.S. Geological Survey Open-File Report 91-536, 99 p.

BCF3 documentation describes the addition of alternate interblock transmissivities. The BCF3 code includes the capabilities of BCF1 and BCF2:

**Goode, D.J. and Appel, C.A., 1992,**Finite-difference interblock transmissivity for unconfined aquifers and for aquifers having smoothly varying transmissivity: U.S. Geological Survey Water Resources Investigations Report 92-4124, 79 p.- The HFB1 Package is documented in:

**Hsieh, P.A. and Freckleton, J.R., 1993,**Documentation of a computer program to simulate horizontal-flow barriers using the U.S. Geological Survey modular three-dimensional finite-difference ground-water flow model: U.S. Geological Survey Open-File Report 92-477, 32 p.- The Transient-Leakage Package (TLK1) is documented in:

**Leake, S.A., Leahy, P. Patrick, and Navoy, Anthony, S., 1994,**Documentation of a computer program to simulate transient leakage from confining units using the modular finite-difference ground-water flow model: U.S.Geological Survey Open-File Report 94-59, 70 p.

A graphical interface to the groundwater model MODFLOW

(DoD Groundwater Modeling System: MODFLOW Interface for preprocessing, postprocessing, graphics, GIS Interface)

MODFLOWP , MODFLOW with Parameter Estimation

IGWMC Modflow Conference 1998

Geotechnical and Geo-Environmental Software Directory

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