Geoscience Reference
In-Depth Information
F
F
c
t i m e
t
c r 1
t
p
Fig. 9.17 Illustration of the time compression method, as given by Equation (9.92), to estimate the cumulative
infiltration
F
(heavy line), resulting from precipitation rate
P
. In this version of the method the time to
ponding is determined independently, and presumed to be correct. At the time of ponding
t
=
t
p
, the
value of
F
is equal to that of the
F
c
curve at
t
=
t
cr
, but its slope is not equal to that of the
F
c
curve at
t
=
t
cr
; thus, the infiltration rate
f
has a discontinuity at
t
=
t
p
, but the infiltrated volume
F
satisfies
the main premise of time compression.
F
c
F
time
t
cr2
t
p
Fig. 9.18 Illustration of the time compression method as given by (9.92), to estimate the cumulative infiltration
F
(heavy line), resulting from precipitation rate
P
. In this version of the method, the time to ponding
is calculated by assuming that, beside Equation (9.91), Equation (9.95) also holds. At the time
t
=
t
p
both
F
and its slope, i.e. the infiltration rate
f
, are equal to the corresponding values of the
F
c
curve
starting at
t
=
0. However, this procedure does not produce the correct value of
t
p
.
