<s>
MODFLOW	B-Application
is	O
the	O
U.S.	O
Geological	O
Survey	O
modular	O
finite-difference	B-Algorithm
flow	O
model	O
,	O
which	O
is	O
a	O
computer	O
code	O
that	O
solves	B-Algorithm
the	O
groundwater	O
flow	O
equation	O
.	O
</s>
<s>
The	O
source	O
code	O
is	O
free	B-Application
public	B-Application
domain	I-Application
software	I-Application
,	O
written	O
primarily	O
in	O
Fortran	B-Application
,	O
and	O
can	O
compile	O
and	O
run	O
on	O
Microsoft	B-Application
Windows	I-Application
or	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
.	O
</s>
<s>
There	O
are	O
several	O
actively	O
developed	O
commercial	O
and	O
non-commercial	O
graphical	B-Application
user	I-Application
interfaces	I-Application
for	O
MODFLOW	B-Application
.	O
</s>
<s>
MODFLOW	B-Application
was	O
constructed	O
in	O
what	O
was	O
in	O
1980	O
's	O
called	O
a	O
modular	O
design	O
.	O
</s>
<s>
If	O
a	O
programmer	O
wants	O
to	O
change	O
something	O
in	O
MODFLOW	B-Application
,	O
the	O
clean	O
organization	O
makes	O
it	O
easy	O
.	O
</s>
<s>
Indeed	O
,	O
this	O
kind	O
of	O
innovation	O
is	O
exactly	O
what	O
was	O
anticipated	O
when	O
MODFLOW	B-Application
was	O
designed	O
.	O
</s>
<s>
Importantly	O
,	O
the	O
modularity	O
of	O
MODFLOW	B-Application
makes	O
it	O
possible	O
for	O
different	O
Packages	O
to	O
be	O
written	O
that	O
are	O
intended	O
to	O
address	O
the	O
same	O
simulation	O
goal	O
in	O
different	O
ways	O
.	O
</s>
<s>
Models	O
like	O
MODFLOW	B-Application
make	O
this	O
kind	O
of	O
testing	O
more	O
definitive	O
and	O
controlled	O
.	O
</s>
<s>
The	O
governing	O
partial	O
differential	O
equation	O
for	O
a	O
confined	O
aquifer	O
used	O
in	O
MODFLOW	B-Application
is	O
:	O
</s>
<s>
The	O
finite	B-Algorithm
difference	I-Algorithm
form	O
of	O
the	O
partial	O
differential	O
in	O
a	O
discretized	B-Algorithm
aquifer	O
domain	O
(	O
represented	O
using	O
rows	O
,	O
columns	O
and	O
layers	O
)	O
is	O
:	O
</s>
<s>
The	O
principal	O
components	O
of	O
anisotropy	O
of	O
the	O
hydraulic	O
conductivity	O
used	O
in	O
MODFLOW	B-Application
is	O
displayed	O
on	O
the	O
right	O
.	O
</s>
<s>
This	O
tensor	B-Device
does	O
not	O
allow	O
non-orthogonal	O
anisotropies	O
,	O
as	O
could	O
be	O
expected	O
from	O
flow	O
in	O
fractures	O
.	O
</s>
<s>
The	O
USGS	O
throughout	O
the	O
1970s	O
had	O
developed	O
several	O
hundred	O
models	O
,	O
written	O
in	O
different	O
dialects	O
of	O
FORTRAN	B-Application
.	O
</s>
<s>
The	O
concept	O
for	O
MODFLOW	B-Application
was	O
originally	O
designed	O
in	O
1981	O
to	O
provide	O
a	O
common	O
modular	O
groundwater	O
model	O
,	O
which	O
could	O
be	O
compiled	O
on	O
multiple	O
platforms	O
without	O
major	O
(	O
or	O
any	O
)	O
modification	O
,	O
and	O
can	O
read	O
and	O
write	O
common	O
formats	O
.	O
</s>
<s>
The	O
original	O
name	O
of	O
the	O
code	O
was	O
"	O
The	O
USGS	O
Modular	O
Three-Dimensional	O
Finite-Difference	B-Algorithm
Ground-Water	O
Flow	O
Model	O
"	O
,	O
or	O
informally	O
as	O
"	O
The	O
Modular	O
Model.	O
"	O
</s>
<s>
The	O
name	O
MODFLOW	B-Application
was	O
coined	O
several	O
years	O
after	O
the	O
initial	O
code	O
development	O
,	O
which	O
started	O
in	O
1981	O
.	O
</s>
<s>
The	O
first	O
version	O
of	O
MODFLOW	B-Application
was	O
published	O
on	O
December	O
28	O
,	O
1983	O
,	O
and	O
was	O
coded	O
entirely	O
in	O
FORTRAN	B-Application
66	O
.	O
</s>
<s>
This	O
version	O
of	O
MODFLOW	B-Application
was	O
rewritten	O
in	O
FORTRAN	B-Application
77	O
,	O
and	O
was	O
originally	O
released	O
on	O
July	O
24	O
,	O
1987	O
.	O
</s>
<s>
MODPATH	O
,	O
was	O
initially	O
developed	O
in	O
1989	O
to	O
post-process	O
the	O
steady-state	O
MODFLOW-88	O
data	O
to	O
determine	O
three-dimensional	O
pathlines	B-Application
of	O
particles	O
.	O
</s>
<s>
It	O
is	O
still	O
used	O
as	O
a	O
post-processor	O
in	O
recent	O
versions	O
of	O
MODFLOW	B-Application
.	O
</s>
<s>
A	O
separate	O
program	O
,	O
MODFLOWP	B-Application
,	O
was	O
developed	O
in	O
1992	O
to	O
estimate	O
various	O
parameters	O
used	O
in	O
MODFLOW	B-Application
.	O
</s>
<s>
This	O
program	O
was	O
eventually	O
built	O
into	O
MODFLOW-2000	O
.	O
</s>
<s>
MODFLOW-96	O
(	O
version	O
3.0	O
)	O
was	O
originally	O
released	O
on	O
December	O
3	O
,	O
1996	O
,	O
and	O
is	O
a	O
cleaned-up	O
and	O
revised	O
continuation	O
of	O
MODFLOW-88	O
.	O
</s>
<s>
There	O
are	O
three	O
final	O
releases	O
of	O
MODFLOW-96	O
:	O
</s>
<s>
Several	O
graphical	B-Application
interfaces	I-Application
were	O
first	O
developed	O
using	O
the	O
MODFLOW-96	O
code	O
.	O
</s>
<s>
MODFLOW-2000	O
(	O
version	O
1.0	O
;	O
version	O
numbering	O
was	O
reset	O
)	O
was	O
released	O
on	O
July	O
20	O
,	O
2000	O
,	O
which	O
merged	O
MODFLOWP	B-Application
and	O
HYDMOD	O
codes	O
into	O
the	O
main	O
program	O
and	O
has	O
integrated	O
observation	O
,	O
sensitivity	O
analysis	O
,	O
parameter	O
estimation	O
,	O
and	O
uncertainty	O
evaluation	O
capabilities	O
.	O
</s>
<s>
Many	O
new	O
packages	O
and	O
enhancements	O
were	O
also	O
included	O
,	O
including	O
new	O
solvers	B-Application
,	O
stream	O
and	O
saturated	O
flow	O
packages	O
.	O
</s>
<s>
This	O
version	O
was	O
coded	O
in	O
a	O
mixture	O
of	O
FORTRAN	B-Application
77	O
,	O
Fortran	B-Application
90	O
,	O
and	O
one	O
solver	B-Application
was	O
programmed	O
in	O
C	B-Language
.	O
MODFLOW-2000	O
can	O
also	O
be	O
compiled	O
for	O
parallel	B-Operating_System
computing	I-Operating_System
,	O
which	O
can	O
allow	O
multiple	O
processors	O
to	O
be	O
used	O
to	O
increase	O
model	O
complexity	O
and/or	O
reduce	O
simulation	O
time	O
.	O
</s>
<s>
The	O
parallelization	B-Operating_System
capability	O
is	O
designed	O
to	O
support	O
the	O
sensitivity	O
analysis	O
,	O
parameter	O
estimation	O
,	O
and	O
uncertainty	O
analysis	O
capabilities	O
of	O
MODFLOW-2000	O
.	O
</s>
<s>
The	O
final	O
version	O
of	O
(	O
or	O
MF2K	B-Application
)	O
is	O
version	O
1.19.01	O
,	O
released	O
on	O
March	O
25	O
,	O
2010	O
.	O
</s>
<s>
There	O
are	O
four	O
related	O
or	O
branched	B-General_Concept
codes	O
based	O
on	O
MODFLOW-2000	O
:	O
</s>
<s>
MODFLOW-2005	O
differs	O
from	O
MODFLOW-2000	O
in	O
that	O
the	O
sensitivity	O
analysis	O
,	O
parameter	O
estimation	O
,	O
and	O
uncertainty	O
evaluation	O
capabilities	O
are	O
removed	O
.	O
</s>
<s>
Thus	O
,	O
the	O
support	O
for	O
these	O
capabilities	O
now	O
falls	O
to	O
"	O
clip	O
on	O
"	O
codes	O
that	O
are	O
supported	O
externally	O
to	O
the	O
MODFLOW	B-Application
support	O
effort	O
.	O
</s>
<s>
In	O
addition	O
,	O
the	O
code	O
was	O
reorganized	O
to	O
support	O
multiple	O
models	O
within	O
one	O
MODFLOW	B-Application
run	O
,	O
as	O
needed	O
for	O
the	O
(	O
Local	O
Grid	O
Refinement	O
)	O
capability	O
.	O
</s>
<s>
MODFLOW-2005	O
is	O
written	O
primarily	O
in	O
Fortran	B-Application
90	O
and	O
C	B-Language
,	O
with	O
C	B-Language
being	O
used	O
for	O
one	O
solver	B-Application
.	O
</s>
<s>
Related	O
or	O
branched	B-General_Concept
codes	O
include	O
:	O
</s>
<s>
(	O
version	O
1.00.12	O
,	O
October	O
1	O
,	O
2016	O
)	O
,	O
The	O
One-Water	O
Hydrologic	O
Flow	O
Model	O
(	O
MODFLOW-OWHM	O
,	O
MF-OWHM	O
or	O
One-Water	O
)	O
,	O
developed	O
cooperatively	O
between	O
the	O
USGS	O
and	O
the	O
U.S.	O
Bureau	O
of	O
Reclamation	O
,	O
is	O
a	O
fusion	O
of	O
multiple	O
versions	O
of	O
MODFLOW-2005	O
(	O
NWT	O
,	O
LGR	O
,	O
FMP	O
,	O
SWR	O
,	O
SWI	O
)	O
into	O
ONE	O
version	O
,	O
contains	O
upgrades	O
and	O
new	O
features	O
and	O
allows	O
the	O
simulation	O
of	O
head-dependent	O
flows	O
,	O
flow-dependent	O
flows	O
,	O
and	O
deformation	O
dependent	O
flows	O
that	O
collectively	O
affect	O
conjunctive	O
use	O
of	O
water	O
resources	O
.	O
</s>
<s>
All	O
version	O
of	O
MODFLOW	B-Application
listed	O
above	O
are	O
constructed	O
on	O
what	O
is	O
called	O
a	O
structured	O
grid	O
.	O
</s>
<s>
Experimentation	O
with	O
a	O
much	O
more	O
flexible	O
grid	O
structure	O
resulted	O
in	O
the	O
release	O
of	O
(	O
version	O
1.3.00	O
,	O
December	O
1	O
,	O
2015	O
)	O
,	O
designed	O
to	O
be	O
adapted	O
to	O
a	O
wide	O
range	O
of	O
grid	O
variations	O
using	O
unstructured	B-Algorithm
grids	I-Algorithm
.	O
</s>
<s>
MODFLOW-USG	O
has	O
similar	O
capabilities	O
as	O
MODFLOW	B-Application
6	I-Application
,	O
which	O
provides	O
grid	O
capabilities	O
with	O
and	O
intermediate	O
level	O
of	O
flexibility	O
.	O
</s>
<s>
MODFLOW	B-Application
6	I-Application
(	O
MF6	O
)	O
,	O
first	O
released	O
in	O
2017	O
,	O
is	O
the	O
sixth	O
core	O
version	O
of	O
MODFLOW	B-Application
to	O
be	O
released	O
by	O
the	O
USGS	O
.	O
</s>
<s>
This	O
release	O
is	O
a	O
rewrite	O
of	O
MODFLOW	B-Application
following	O
an	O
object-oriented	O
programming	O
paradigm	O
in	O
Fortran	B-Application
,	O
and	O
provides	O
a	O
platform	O
that	O
includes	O
the	O
capabilities	O
from	O
several	O
previous	O
MODFLOW-2005	O
versions	O
,	O
including	O
MODFLOW-NWT	B-Application
,	O
MODFLOW-USG	O
,	O
and	O
MODFLOW-LGR	O
.	O
</s>
<s>
MODFLOW	B-Application
6	I-Application
supports	O
structured	O
or	O
unstructured	B-Algorithm
grids	I-Algorithm
,	O
has	O
full	O
support	O
for	O
the	O
Newton-Raphson	O
formulation	O
,	O
and	O
has	O
a	O
unique	O
Water	O
Mover	O
Package	O
that	O
allows	O
flows	O
to	O
be	O
routed	O
between	O
the	O
advanced	O
packages	O
,	O
including	O
the	O
Streamflow	O
Routing	O
,	O
Lake	O
,	O
Multi-Aquifer	O
Well	O
,	O
and	O
Unsaturated	O
Zone	O
Flow	O
Packages	O
.	O
</s>
<s>
MODFLOW	B-Application
6	I-Application
also	O
contains	O
a	O
Groundwater	O
Transport	O
(	O
GWT	O
)	O
model	O
that	O
simulates	O
transient	O
three-dimensional	O
solute	O
transport	O
on	O
structured	O
or	O
unstructured	B-Algorithm
grids	I-Algorithm
and	O
through	O
the	O
advanced	O
flow	O
and	O
mover	O
packages	O
.	O
</s>
<s>
An	O
Application	O
Programming	O
Interface	O
(	O
API	O
)	O
is	O
also	O
available	O
for	O
MODFLOW	B-Application
6	I-Application
,	O
which	O
allows	O
the	O
program	O
to	O
be	O
coupled	O
with	O
other	O
models	O
or	O
controlled	O
with	O
popular	O
scripting	O
languages	O
,	O
such	O
as	O
Python	O
.	O
</s>
<s>
While	O
there	O
are	O
a	O
few	O
features	O
lacking	O
in	O
the	O
current	O
release	O
that	O
are	O
supported	O
in	O
MODFLOW-2005	O
,	O
most	O
of	O
the	O
popular	O
capabilities	O
in	O
previous	O
MODFLOW	B-Application
versions	O
are	O
available	O
in	O
MODFLOW	B-Application
6	I-Application
.	O
</s>
<s>
The	O
names	O
in	O
this	O
table	O
are	O
the	O
labels	O
used	O
to	O
turn	O
MODFLOW	B-Application
capabilities	O
on	O
and	O
off	O
via	O
a	O
key	O
input	O
file	O
.	O
</s>
<s>
Many	O
of	O
the	O
capabilities	O
introduced	O
are	O
supported	O
in	O
later	O
versions	O
,	O
though	O
the	O
grid	O
change	O
enabled	O
with	O
MODFLOW-USG	O
and	O
MODFLOW	B-Application
6	I-Application
meant	O
that	O
such	O
backward	O
compatibility	O
was	O
rather	O
selective	O
.	O
</s>
<s>
There	O
are	O
several	O
graphical	B-Application
interfaces	I-Application
to	O
MODFLOW	B-Application
,	O
which	O
often	O
include	O
the	O
compiled	O
MODFLOW	B-Application
code	O
with	O
modifications	O
.	O
</s>
<s>
These	O
programs	O
aid	O
the	O
input	O
of	O
data	O
for	O
creating	O
MODFLOW	B-Application
models	O
.	O
</s>
<s>
Non-commercial	O
MODFLOW	B-Application
versions	O
are	O
free	B-Application
,	O
however	O
,	O
their	O
licensing	O
usually	O
limit	O
the	O
use	O
to	O
non-profit	O
educational	O
or	O
research	O
purposes	O
.	O
</s>
<s>
is	O
a	O
grid-independent	O
graphical	B-Application
user	I-Application
interface	I-Application
from	O
the	O
USGS	O
for	O
MODFLOW	B-Application
6	I-Application
,	O
MODPATH	O
,	O
SUTRA	O
,	O
and	O
PHAST	O
version	O
1.51	O
.	O
</s>
<s>
is	O
a	O
Python	O
package	O
for	O
creating	O
,	O
running	O
,	O
and	O
post-processing	O
MODFLOW-based	O
models	O
.	O
</s>
<s>
–	O
Made	O
by	O
the	O
USGS	O
:	O
it	O
is	O
updated	O
often	O
to	O
match	O
the	O
current	O
USGS	O
MODFLOW	B-Application
development	O
.	O
</s>
<s>
It	O
supports	O
MODFLOW-96	O
,	O
MODFLOW-2000	O
,	O
MODFLOW-2005	O
,	O
MODPATH	O
,	O
ZONEBUDGET	O
,	O
GWT	O
,	O
MT3DMS	B-Application
,	O
SEAWAT	O
,	O
and	O
GWM	O
.	O
</s>
<s>
Source	O
code	O
for	O
MODFLOW-GUI	O
is	O
included	O
.	O
</s>
<s>
–	O
"	O
Processing	O
MODFLOW	B-Application
"	O
(	O
for	O
Windows	B-Application
)	O
–	O
powerful	O
freeware	O
for	O
MODFLOW	B-Application
processing	O
and	O
visualization	O
,	O
provided	O
alongside	O
an	O
instructional	O
book	O
;	O
also	O
available	O
in	O
Traditional	O
Chinese	O
.	O
</s>
<s>
-	O
mflab	O
is	O
a	O
MATLAB	B-Language
interface	O
to	O
MODFLOW	B-Application
.	O
</s>
<s>
The	O
user	O
builds	O
and	O
analyzes	O
models	O
by	O
writing	O
a	O
set	O
of	O
MATLAB	B-Language
scripts	O
.	O
</s>
<s>
-	O
Free	B-Application
and	O
open	O
source	O
interface	O
developed	O
by	O
.	O
</s>
<s>
iMOD	O
contains	O
an	O
accelerated	O
version	O
of	O
MODFLOW	B-Application
with	O
fast	O
,	O
flexible	O
and	O
consistent	O
sub-domain	O
modeling	O
techniques	O
.	O
</s>
<s>
is	O
a	O
free	B-Application
and	O
open	O
source	O
,	O
QGIS-integrated	O
modelling	O
platform	O
integrating	O
MODFLOW	B-Application
(	O
MODFLOW	B-Application
versions	O
integrated	O
are	O
MODFLOW-2005	O
and	O
MODFLOW-OWHM	O
)	O
and	O
the	O
following	O
MODFLOW-related	O
simulation	O
codes	O
:	O
,	O
,	O
,	O
,	O
,	O
.	O
</s>
<s>
FREEWAT	O
has	O
been	O
developed	O
in	O
the	O
framework	O
of	O
the	O
H2020	O
FREEWAT	O
project	O
(	O
FREE	B-Application
and	I-Application
open	I-Application
source	I-Application
software	I-Application
tools	O
for	O
WATer	O
resource	O
management	O
)	O
,	O
financed	O
by	O
the	O
EU	O
Commission	O
under	O
the	O
call	O
WATER	O
INNOVATION	O
:	O
BOOSTING	O
ITS	O
VALUE	O
FOR	O
EUROPE	O
.	O
</s>
<s>
Commercial	O
MODFLOW	B-Application
programs	O
are	O
typically	O
used	O
by	O
governments	O
and	O
consultants	O
for	O
practical	O
applications	O
of	O
MODFLOW	B-Application
to	O
real-world	O
groundwater	O
problems	O
.	O
</s>
<s>
Professional	O
versions	O
of	O
MODFLOW	B-Application
are	O
generally	O
priced	O
at	O
a	O
minimum	O
of	O
around	O
$1000	O
and	O
typically	O
range	O
upward	O
to	O
US$7000	O
.	O
</s>
<s>
This	O
is	O
a	O
list	O
of	O
commercial	O
programs	O
for	O
MODFLOW	B-Application
:	O
</s>
<s>
All	O
current	O
versions	O
of	O
these	O
programs	O
run	O
only	O
on	O
Microsoft	B-Application
Windows	I-Application
,	O
however	O
previous	O
versions	O
of	O
GMS	B-Application
(	O
up	O
to	O
Version	O
3.1	O
)	O
were	O
compiled	O
for	O
several	O
Unix	B-Application
platforms	O
.	O
</s>
<s>
ModelCad	O
–	O
A	O
Windows-based	O
interface	O
,	O
developed	O
by	O
Geraghty	O
and	O
Miller	O
,	O
Inc	O
.	O
</s>
<s>
–	O
A	O
DOS-based	O
interface	O
by	O
S.S.	O
Papadopulos	O
&	O
Associates	O
,	O
Inc	O
.	O
</s>
