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mfusg.txt
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U.S. Geological Survey (USGS) modflow-usg(1)
NOTE: Any use of trade, product or firm names is for descriptive
purposes only and does not imply endorsement by the U.S.
Government.
NAME
MODFLOW-USG - Modular unstructured three-dimensional finite-
difference groundwater model
ABSTRACT
A new version of MODFLOW, called MODFLOW–USG (for UnStructured
Grid), was developed to support a wide variety of structured and
unstructured grid types, including nested grids and grids based on
prismatic triangles, rectangles, hexagons, and other cell shapes.
Flexibility in grid design can be used to focus resolution along
rivers and around wells, for example, or to subdiscretize
individual layers to better represent hydrostratigraphic units.
MODFLOW–USG is based on an underlying control volume finite
difference (CVFD) formulation in which a cell can be connected to
an arbitrary number of adjacent cells. To improve accuracy of the
CVFD formulation for irregular grid-cell geometries or nested
grids, a generalized Ghost Node Correction (GNC) Package was
developed, which uses interpolated heads in the flow calculation
between adjacent connected cells. MODFLOW–USG includes a
Groundwater Flow (GWF) Process, based on the GWF Process in
MODFLOW–2005, as well as a new Connected Linear Network (CLN)
Process to simulate the effects of multi-node wells, karst
conduits, and tile drains, for example. The CLN Process is tightly
coupled with the GWF Process in that the equations from both
processes are formulated into one matrix equation and solved
simultaneously. This robustness results from using an unstructured
grid with unstructured matrix storage and solution schemes.
MODFLOW–USG also contains an optional Newton-Raphson formulation,
based on the formulation in MODFLOW–NWT, for improving solution
convergence and avoiding problems with the drying and rewetting of
cells. Because the existing MODFLOW solvers were developed for
structured and symmetric matrices, they were replaced with a new
Sparse Matrix Solver (SMS) Package developed specifically for
MODFLOW–USG. The SMS Package provides several methods for resolving
nonlinearities and multiple symmetric and asymmetric linear
solution schemes to solve the matrix arising from the flow
equations and the Newton-Raphson formulation, respectively.
METHOD
The groundwater flow equation is solved using the finite-difference
approximation. The flow region is subdivided into blocks in which
the medium properties are assumed to be uniform. In plan view the
blocks are made from a grid of mutually perpendicular lines that may
be variably spaced. Model layers can have varying thickness. A
flow equation is written for each block, called a cell. A sparse
matrix solver is provided for solving the resulting matrix problem;
the user can choose the best solver for the particular problem.
Flow-rate and cumulative-volume balances from each type of inflow
and outflow are computed for each time step.
HISTORY
MODFLOW-USG Version 1.4.00 10/27/2017 -- Added the Segmented
Evapotranspiration and Drain with Return Flow Packages.
This change, bug fixes, and other changes are described
in release.txt.
MODFLOW-USG Version 1.3.00 12/01/2015 -- Added DDREFERENCE
capability, similar to the capability available in MODFLOW-2005.
This change, bug fixes, and other minor changes are described in
release.txt.
MODFLOW-USG Version 1.2.00 03/21/2014 -- Added a transient IBOUND
option and an IA-JA input option for the CLN Process. These and
other minor changes are described in release.txt.
MODFLOW-USG Version 1.1.00 08/23/2013 -- Added bi-conjugate
gradient stabilized acceleration method for the pcgu linear solver.
Added free format option for the STR Package. See release.txt for
a full description of the changes.
MODFLOW-USG Version 1.00.00 05/03/2013 -- First release.
DATA REQUIREMENTS
In order to use MODFLOW-USG, initial conditions, hydraulic
properties, and stresses must be specified for every model cell in
the finite- difference grid. Input data are read from files.
SYSTEM REQUIREMENTS
MODFLOW-USG is written in Fortran 90 with some Fortran 2003
extensions. The code has been used on personal computers running
various forms of the Microsoft Windows operating system.
FUNTIONALITY
This version of MODFLOW-USG includes the following functionality that is
documented in Panday and others (2013).
BAS -- Basic Package
BCF -- Block-Centered Flow Package
LPF -- Layer-Property Flow Package
HFB -- Horizontal Flow Barrier Package
CHD -- Time-Variant Specified-Head Option
RIV -- River Package
DRN -- Drain Package
WEL -- Well Package
GHB -- General Head Boundary Package
RCH -- Recharge Package
EVT -- Evapotranspiration Package
STR -- Streamflow-Routing Package
FHB -- Flow and Head Boundary Package
SUB -- Subsidence Package
SFR -- Streamflow-Routing Package
LAK -- Lake Package
GAG -- Gage Package
SMS -- Sparse Matrix Solver Package
DOCUMENTATION
The basic documentation for MODFLOW-USG is contained in:
Panday, Sorab, Langevin, C.D., Niswonger, R.G., Ibaraki, Motomu, and
Hughes, J.D., 2013, MODFLOW–USG version 1: An unstructured grid version
of MODFLOW for simulating groundwater flow and tightly coupled processes
using a control volume finite-difference formulation: U.S. Geological
Survey Techniques and Methods, book 6, chap. A45, 66 p.
The basic documentation for MODFLOW-2005, which contains information for
many of the packages in MODFLOW-USG, is contained in:
Harbaugh, A.W., 2005, MODFLOW-2005, the U.S. Geological Survey modular
ground-water model -- the Ground-Water Flow Process: U.S. Geological Survey
Techniques and Methods 6-A16, variously p.
The STR 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 FHB Package is documented in:
Leake, S.A., and Lilly, M.R., 1997, Documentation of a computer program
(FHB1) for assignment of transient specified-flow and specified-head
boundaries in applications of the modular finite- difference ground-water
flow model (MODFLOW): U.S. Geological Survey Open-File Report 97-571, 50 p.
The SUB Package is documented in:
Hoffmann, Jorn, Leake, S.A., Galloway, D.L., and Wilson, A.M., 2003,
MODFLOW-2000 ground-water model -- User guide to the Subsidence and
Aquifer-System Compaction (SUB) Package: U.S. Geological Survey Open-File
Report 03-233, 46 p.
The SFR Package is documented in:
Prudic, D.E., Konikow, L.F., and Banta, E.R., A new Streamflow-Routing
(SFR1) Package to simulate stream-aquifer interaction with MODFLOW-2000:
U.S. Geological Survey Open File Report 2004-1042, 95 p.
Niswonger, R.G., and Prudic, D.E., 2005, Documentation of the
Streamflow-Routing (SFR2) Package to include unsaturated flow beneath
streams -- a modification to SFR1: U.S. Geological Techniques and Methods
Book 6, Chapter A13, 47 p.
The LAK Package is documented in:
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: Water-Resources
Investigations Report 00-4167, 146 p.
The GAG Package is documented as part of the above SFR and LAK
documentation.
The DRT and ETS Packages are documented in:
Banta, E.R., 2000, MODFLOW-2000, the U.S. Geological Survey modular
ground-water model -- documentation of packages for simulating
evapotranspiration with a segmented function (ETS1) and drains with return
flow (DRT1): U.S. Geological Survey Open-File Report 00-466, 127 p.
CONTACTS
U.S. Geological Survey
Office of Groundwater
411 National Center
Reston, VA 20192
(703) 648-5001
ogw_webmaster@usgs.gov