Geoscience Reference
In-Depth Information
In both instances we are dealing with two terms. One is the infi ltration rate
q
0
that
is equivalent to a velocity, directly related to rain intensity and frequently measured
as mm/min. Cumulative infi ltration
I
is the second term. It is the sum of infi ltrated
water from the start of infi ltration up to a specifi c time, related to the “depth” of the
rain and measured in units of millimeter or centimeter. Let us mention that one
millimeter of rainfall is the equivalent of 1 l of water per square meter.
10.1.1
Infi ltration from the Suddenly Flooded Soil
Infi ltration of water into a soil suddenly fl ooded with water is characterized by an
initially very high infi ltration rate
q
0
many times higher than the saturated conduc-
tivity
K
S
, quickly decreases, and monotonically approaches
K
S
; see Fig.
10.1
. From
Chap.
9
,
we know that two forces are involved - one varies with time, while the
other is constant. The force of the pressure potential gradient is extremely high
when the soil is initially dry and wetting by infi ltration but diminishes to nearly
trivial values compared with the force of gravity as the topsoil wets to nearly the
same soil water content within the topsoil. We can compare it to the thirst of a man
who did not get a drop of water during a long, hot day. He very quickly drinks the
fi rst gulp, but gradually as he is quenching his extreme thirst, he drinks slowly and
Fig. 10.1
Time dependence of the cumulative infi ltration
I
(
t
) and of the infi ltration rate
q
0
(
t
) when
the soil surface is suddenly fl ooded, i.e., at fl ood infi ltration, when the soil is not fully saturated by
