Geoscience Reference
In-Depth Information
Increase
n
Increase
α
θ
res
θ
sat
Water content (cm
3
cm
-3
)
= range
θ
sat
θ
res
-
Figure 4.21
Analytical equation for retention function (Eq. (
4.23
)), showing the
effect of the four shape parameters.
where
θ
s
is the saturated water content (m
3
m
-3
),
θ
r
is the residual water content
(m
3
m
-3
),
α
is an empirical shape parameter (m
-1
) related to the coarseness of the soil
texture and
n
is an empirical shape parameter (-) related to the width of the particle
size distribution. The inluence of the four parameters describing
θ
(
h
) is depicted in
Figure 4.21
.
Earlier Mualem (
1976
) had introduced a very useful predictive model of the
k
(
θ
)
relation based on pore-size hydraulic considerations. In combination with Eq. (
4.23
),
Mualem's predictive model results in the following expression for
k
(
θ
):
2
n
−
1
n
n
λ
k
(
θ
=
k S
11
− −
S
(4.24)
n
−
1
se
e
where
k
s
is the saturated hydraulic conductivity (m d
-1
),
λ
is an exponent (-) related to
pore connectivity, and
S
e
is the relative saturation (-):
=
−
−
θθ
θθ
S
e
r
(4.25)
s
r
Figure 4.22
shows the effect of itting parameters
k
s
and
λ
on the conductivity func-
tion. Equations (
4.23
)-(
4.25
) form the basis of several national and international
databanks (e.g., Carsel and Parrish,
1988
; Yates et al.,
1992
; Leij et al.,
1996
; Wösten
et al.,
1998
; Wösten et al.,
2001
).
4.8 Iniltration
Iniltration refers to water entry into a soil from one of its edges. Generally, it refers
to vertical iniltration, where water moves downward from the soil surface into deeper
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