<s>
HydroGeoSphere	B-Application
(	O
HGS	O
)	O
is	O
a	O
3D	O
control-volume	O
finite	B-Application
element	I-Application
groundwater	O
model	B-Application
,	O
and	O
is	O
based	O
on	O
a	O
rigorous	O
conceptualization	O
of	O
the	O
hydrologic	O
system	O
consisting	O
of	O
surface	O
and	O
subsurface	O
flow	O
regimes	O
.	O
</s>
<s>
The	O
model	B-Application
is	O
designed	O
to	O
take	O
into	O
account	O
all	O
key	O
components	O
of	O
the	O
hydrologic	O
cycle	O
.	O
</s>
<s>
For	O
each	O
time	O
step	O
,	O
the	O
model	B-Application
solves	O
surface	O
and	O
subsurface	O
flow	O
,	O
solute	O
and	O
energy	O
transport	O
equations	O
simultaneously	O
,	O
and	O
provides	O
a	O
complete	O
water	O
and	O
solute	O
balance	O
.	O
</s>
<s>
The	O
original	O
name	O
for	O
the	O
code	O
was	O
FRAC3DVS	B-Application
,	O
which	O
was	O
created	O
by	O
René	O
Therrien	O
in	O
1992	O
.	O
</s>
<s>
It	O
was	O
renamed	O
to	O
HydroGeoSphere	B-Application
in	O
2002	O
with	O
the	O
implementation	O
of	O
2D	O
surface	O
water	O
flow	O
and	O
transport	O
.	O
</s>
<s>
In	O
order	O
to	O
accomplish	O
the	O
integrated	O
analysis	O
,	O
HydroGeoSphere	B-Application
utilizes	O
a	O
rigorous	O
,	O
mass	O
conservative	O
modeling	O
approach	O
that	O
fully	O
couples	O
the	O
surface	O
flow	O
and	O
transport	O
equations	O
with	O
the	O
3-D	O
,	O
variably	O
saturated	O
subsurface	O
flow	O
and	O
transport	O
equations	O
.	O
</s>
<s>
HydroGeoSphere	B-Application
assumes	O
that	O
the	O
subsurface	O
flow	O
equation	O
in	O
a	O
porous	O
medium	O
is	O
always	O
solved	O
during	O
a	O
simulation	O
,	O
either	O
for	O
fully	O
saturated	O
or	O
variably	O
saturated	O
flow	O
conditions	O
.	O
</s>
<s>
surface	O
water	O
,	O
wells	O
,	O
and	O
tile	O
drains	O
)	O
,	O
is	O
the	O
external	O
fluid	O
outside	O
of	O
the	O
model	B-Application
domain	O
,	O
is	O
the	O
saturated	O
water	O
content	O
,	O
is	O
the	O
degree	O
of	O
saturation	O
,	O
is	O
the	O
hydraulic	O
conductivity	O
tensor	O
,	O
is	O
the	O
relative	O
permeability	O
of	O
the	O
medium	O
calculated	O
as	O
a	O
function	O
of	O
saturation	O
,	O
is	O
the	O
pressure	O
head	O
,	O
and	O
is	O
the	O
elevation	O
head	O
.	O
</s>
<s>
Areal	O
surface	O
water	O
flow	O
is	O
represented	O
in	O
HydroGeoSphere	B-Application
by	O
a	O
two-dimensional	O
depth-averaged	O
flow	O
equation	O
,	O
which	O
is	O
the	O
diffusion-wave	O
approximation	O
of	O
the	O
Saint	O
Venant	O
equation	O
for	O
surface	O
water	O
flow	O
.	O
</s>
<s>
HydroGeoSphere	B-Application
's	O
surface	O
water	O
flow	O
component	O
is	O
implemented	O
with	O
the	O
following	O
assumptions	O
:	O
</s>
<s>
Graf	O
 [ 2005 ] 	O
incorporated	O
heat	O
transport	O
within	O
the	O
saturated-zone	O
flow	O
regime	O
into	O
HydroGeoSphere	B-Application
together	O
with	O
temperature-dependent	O
fluid	O
properties	O
,	O
such	O
as	O
viscosity	O
and	O
density	O
.	O
</s>
<s>
The	O
model	B-Application
’s	O
capability	O
was	O
successfully	O
demonstrated	O
for	O
the	O
case	O
of	O
thermohaline	O
flow	O
and	O
transport	O
in	O
porous	O
and	O
fractured	O
porous	O
media	O
[	O
Graf	O
and	O
Therrien	O
,	O
2007 ]	O
.	O
</s>
<s>
This	O
work	O
extends	O
the	O
model	B-Application
’s	O
capability	O
to	O
include	O
thermal	O
energy	O
transport	O
in	O
the	O
unsaturated	O
zone	O
and	O
in	O
the	O
surface	O
water	O
,	O
which	O
is	O
considered	O
a	O
key	O
step	O
in	O
the	O
linkage	O
between	O
the	O
atmospheric	O
and	O
hydrologic	O
systems	O
.	O
</s>
<s>
As	O
such	O
,	O
surface	O
heat	O
fluxes	O
across	O
the	O
land	O
surface	O
were	O
also	O
incorporated	O
into	O
HydroGeoSphere	B-Application
.	O
</s>
<s>
A	O
complete	O
description	O
of	O
the	O
physical	O
processes	O
and	O
governing	O
flow	O
and	O
solute	O
transport	O
equations	O
that	O
form	O
the	O
basis	O
of	O
HydroGeoSphere	B-Application
can	O
be	O
found	O
in	O
Therrien	O
et	O
al	O
.	O
</s>
<s>
The	O
2-D	O
areal	O
surface	O
flow	O
modules	O
of	O
HydroGeoSphere	B-Application
follow	O
the	O
same	O
conventions	O
for	O
spatial	O
and	O
temporal	O
discretizations	O
as	O
those	O
used	O
by	O
the	O
subsurface	O
modules	O
.	O
</s>
<s>
When	O
the	O
subsurface	O
connection	O
is	O
provided	O
via	O
superposition	O
,	O
HydroGeoSphere	B-Application
adds	O
the	O
surface	O
flow	O
equation	O
terms	O
for	O
the	O
2-D	O
surface	O
mesh	O
to	O
those	O
of	O
the	O
top	O
layer	O
of	O
subsurface	O
nodes	O
.	O
</s>
<s>
The	O
HGS	O
model	B-Application
is	O
a	O
three-dimensional	O
control-volume	O
finite	B-Application
element	I-Application
simulator	O
which	O
is	O
designed	O
to	O
simulate	O
the	O
entire	O
terrestrial	O
portion	O
of	O
the	O
hydrologic	O
cycle	O
.	O
</s>
<s>
Additionally	O
,	O
HydroGeoSphere	B-Application
has	O
been	O
linked	O
to	O
Weather	B-Application
Research	I-Application
and	I-Application
Forecasting	I-Application
,	O
a	O
mesoscale	O
atmospheric	O
model	B-Application
for	O
fully	O
coupled	O
subsurface	O
,	O
surface	O
,	O
and	O
atmospheric	O
simulations	O
.	O
</s>
