<s>
Geographic	B-Application
information	I-Application
systems	I-Application
(	O
GISs	O
)	O
have	O
become	O
a	O
useful	O
and	O
important	O
tool	O
in	O
the	O
field	O
of	O
hydrology	O
to	O
study	O
and	O
manage	O
Earth	O
's	O
water	O
resources	O
.	O
</s>
<s>
Because	O
water	O
in	O
its	O
occurrence	O
varies	O
spatially	O
and	O
temporally	O
throughout	O
the	O
hydrologic	O
cycle	O
,	O
its	O
study	O
using	O
GIS	B-Application
is	O
especially	O
practical	O
.	O
</s>
<s>
Whereas	O
previous	O
GIS	B-Application
systems	O
were	O
mostly	O
static	O
in	O
their	O
geospatial	O
representation	O
of	O
hydrologic	O
features	O
,	O
GIS	B-Application
platforms	O
are	O
becoming	O
increasingly	O
dynamic	O
,	O
narrowing	O
the	O
gap	O
between	O
historical	O
data	O
and	O
current	O
hydrologic	O
reality	O
.	O
</s>
<s>
All	O
of	O
these	O
quantities	O
can	O
be	O
measured	O
or	O
estimated	O
based	O
on	O
environmental	O
data	O
and	O
their	O
characteristics	O
can	O
be	O
graphically	O
displayed	O
and	O
studies	O
using	O
GIS	B-Application
.	O
</s>
<s>
The	O
United	O
States	O
Geological	O
Survey	O
((USGS )	O
)	O
is	O
a	O
publicly	O
available	O
source	O
of	O
remotely	B-Application
sensed	I-Application
hydrological	O
data	O
.	O
</s>
<s>
A	O
benefit	O
of	O
using	O
GIS	B-Application
softwares	I-Application
for	O
hydrological	O
modeling	O
is	O
that	O
digital	O
visualizations	O
of	O
data	O
can	O
be	O
linked	O
to	O
real-time	O
data	O
.	O
</s>
<s>
For	O
surface	O
water	O
modeling	O
,	O
digital	B-Application
elevation	I-Application
model	I-Application
are	O
often	O
layered	O
with	O
hydrographic	O
data	O
in	O
order	O
to	O
determine	O
the	O
boundaries	O
of	O
a	O
watershed	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
the	O
event	O
of	O
snowmelt	O
,	O
the	O
amount	O
of	O
snowfall	O
can	O
be	O
input	O
into	O
GIS	B-Application
to	O
predict	O
the	O
amount	O
of	O
water	O
that	O
will	O
travel	O
downstream	O
.	O
</s>
<s>
Another	O
useful	O
application	O
for	O
GIS	B-Application
regards	O
flood	O
risk	O
assessment	O
.	O
</s>
<s>
Using	O
digital	B-Application
elevation	I-Application
models	I-Application
combined	O
with	O
peak	O
discharge	O
data	O
can	O
predict	O
which	O
areas	O
of	O
a	O
floodplain	O
will	O
be	O
submerged	O
depending	O
on	O
the	O
amount	O
of	O
rainfall	O
.	O
</s>
<s>
The	O
use	O
of	O
GIS	B-Application
to	O
analyze	O
groundwater	O
falls	O
into	O
the	O
field	O
of	O
hydrogeology	O
.	O
</s>
<s>
In	O
some	O
cases	O
,	O
GIS	B-Application
can	O
be	O
used	O
to	O
analyze	O
drainage	O
and	O
groundwater	O
data	O
in	O
order	O
to	O
select	O
suitable	O
sites	O
for	O
groundwater	O
recharge	O
.	O
</s>
