Geoscience Reference
In-Depth Information
Fig. 10.2
Soil water content development
θ
(
z
) at certain time intervals of water infi ltration into
sandy soil (subscript S) and a clayey soil (subscript C) when the soil surface is suddenly fl ooded at
time
t
= 0. With initial and saturated soil water contents being denoted by
θ
i
and
θ
S
, respectively, the
initial water content of the sandy soil is
θ
iS
and that of the clayey soil is
θ
iC
. Similarly, the water-
saturated values are
θ
SS
and
θ
SC
. The numbers at the curves denote the time in seconds after the start
of infi ltration
“infl ow” of water from the rain with the rain intensity distinctly lower than is the
ability of soil to imbibe or soak up water after the start of infi ltration, as we earlier
demonstrated this theoretical ability for fl ood infi ltration in Fig.
10.1
.
During a rain of any intensity, various shapes of soil water content profi les
develop sequentially in phases. Although they roughly resemble those of fl ood infi l-
tration in Fig.
10.2
, there is a very important and distinct difference that becomes
evident when rain comes down at a constant intensity or rate. For an example, we
consider a heavy rain falling at a constant intensity
q
R
that is several times higher
than the value of the saturated conductivity. The soil rapidly becomes progressively
more wet but never gets completely water saturated even at the top of its surface
during the fi rst phase of infi ltration; see curves labeled
t
1
,
t
2
, and
t
3
in Fig.
10.4
. Just
after the start of infi ltration at time
t
1
, the soil water content of the surface is only
