<s>
A	O
runoff	B-Application
model	I-Application
or	O
rainfall-runoff	B-Application
model	I-Application
describes	O
how	O
rainfall	O
is	O
converted	O
into	O
runoff	O
in	O
a	O
drainage	O
basin	O
(	O
catchment	O
area	O
or	O
watershed	O
)	O
.	O
</s>
<s>
More	O
precisely	O
,	O
it	O
produces	O
a	O
surface	O
runoff	B-Application
hydrograph	I-Application
in	O
response	O
to	O
a	O
rainfall	O
event	O
,	O
represented	O
by	O
and	O
input	O
as	O
a	O
hyetograph	O
.	O
</s>
<s>
Rainfall-runoff	B-Application
models	I-Application
need	O
to	O
be	O
calibrated	B-General_Concept
before	O
they	O
can	O
be	O
used	O
.	O
</s>
<s>
A	O
well	O
known	O
runoff	B-Application
model	I-Application
is	O
the	O
linear	O
reservoir	O
,	O
but	O
in	O
practice	O
it	O
has	O
limited	O
applicability	O
.	O
</s>
<s>
The	O
runoff	B-Application
model	I-Application
with	O
a	O
non-linear	O
reservoir	O
is	O
more	O
universally	O
applicable	O
,	O
but	O
still	O
it	O
holds	O
only	O
for	O
catchments	O
whose	O
surface	O
area	O
is	O
limited	O
by	O
the	O
condition	O
that	O
the	O
rainfall	O
can	O
be	O
considered	O
more	O
or	O
less	O
uniformly	O
distributed	O
over	O
the	O
area	O
.	O
</s>
<s>
When	O
the	O
study	O
area	O
is	O
too	O
large	O
,	O
it	O
can	O
be	O
divided	O
into	O
sub-catchments	O
and	O
the	O
various	O
runoff	B-Application
hydrographs	I-Application
may	O
be	O
combined	O
using	O
flood	O
routing	O
techniques	O
.	O
</s>
<s>
The	O
availability	O
of	O
the	O
foregoing	O
runoff	O
equation	O
eliminates	O
the	O
necessity	O
of	O
calculating	O
the	O
total	O
hydrograph	O
by	O
the	O
summation	O
of	O
partial	O
hydrographs	O
using	O
the	O
IUH	O
as	O
is	O
done	O
with	O
the	O
more	O
complicated	O
convolution	B-Language
method	O
.	O
</s>
<s>
With	O
this	O
method	O
the	O
reservoir	O
can	O
be	O
used	O
as	O
a	O
black	B-Device
box	I-Device
model	O
.	O
</s>
<s>
Hence	O
,	O
the	O
reaction	O
or	O
response	O
factor	O
Aq	O
can	O
be	O
determined	O
from	O
runoff	O
or	O
discharge	O
measurements	O
using	O
unit	O
time	O
steps	O
during	O
dry	O
spells	O
,	O
employing	O
a	O
numerical	B-Algorithm
method	I-Algorithm
.	O
</s>
<s>
For	O
calibration	B-General_Concept
,	O
the	O
model	O
requires	O
considerable	O
research	O
.	O
</s>
<s>
Vflo	B-Algorithm
is	O
another	O
software	O
program	O
for	O
modeling	O
runoff	O
.	O
</s>
<s>
Vflo	B-Algorithm
uses	O
radar	B-Application
rainfall	I-Application
and	O
GIS	B-Application
data	O
to	O
generate	O
physics-based	O
,	O
distributed	O
runoff	O
simulation	O
.	O
</s>
<s>
The	O
software	O
is	O
based	O
on	O
object-oriented	O
programming	O
and	O
allows	O
hydrologic	O
and	O
hydraulic	O
modeling	O
according	O
to	O
a	O
semi-distributed	O
conceptual	O
scheme	O
with	O
different	O
rainfall-runoff	B-Application
model	I-Application
such	O
as	O
HBV	O
,	O
GR4J	O
,	O
SAC-SMA	O
or	O
SOCONT	O
.	O
</s>
