Geoscience Reference
In-Depth Information
To obtain the SWD computation accurately, some assumptions were
implemented consciously to a characteristic of soil profile. Those are:
(1) initial SWD is equal to a delta of soil water content (∆
θ
=
θ
t
−
θ
t−
1
),
(2) surface runoff (
RO
) is zero, (3) water quantity from
I
and loss through
drainage is zero, (4) soil and ABL layer are as the thing which are closed
water column system, (5) when rainfall occurs and the water fill in soil
pores dominantly, then the air is suppressed and SWD upward is zero, and
(6) to conserve a water balance in the third layer then an initial SWD in
the fourth layer is equal 0.75 ∆
θ
of the third layer.
According to all of those principles, the equations of SWD from four
soil layers are written as follows:
E
t
f
ew
De
t
(1) =
De
−
(1)
t−
1
−
∆
De
+(2)
t
−
R
t
+
+0
.
4
Tr
t
+∆
DP c
−
(1)
t
,
(1)
De
t
(2) =
De
−
(2)
t−
1
−
∆
De
+(3)
t
+0
.
3
Tr
t
−
∆
DP c
+(1)
t−
1
+∆
DP c
−
(2)
t
,
(2)
De
t
(3) =
De
−
(3)
t−
1
−
∆
De
+(4)
t
+0
.
2
Tr
t
−
∆
DP c
+(2)
t−
1
+∆
DP c
−
(3)
t
,
(3)
∆
DP c
+(3)
t−
1
+∆
DP c
−
(4)
t
,
(4)
where
De
is cumulative SWD (mm),
I
is irrigation infiltrates the soil (mm);
R
,
RO
and
E
(
E
=
ET
o
K
e
) are in mm,
Tr
is in an exposed and wetted
fraction of the soil surface layer (mm) (
Tr
=
ET
o
K
cb
).
7
DP c
is deep per-
colation.
f
w
is fraction of soil surface wetted by irrigation or rainfall and
without its (0
.
01
De
t
(4) =
De
−
(4)
t−
1
+0
.
1
Tr
t
−
1), and
f
ew
is exposed and wetted soil fraction (0.01-1). It
is calculated as
f
ew
=min(1
−
f
c
,f
w
), where
fc
average is exposed soil frac-
tion covered by vegetation (0.01-1). ∆
De
+(
n
)
t
=
De
+(
n
)
t
−
−
De
+(
n
)
t−
1
and
∆
DP c
(
n
)
t
=
DP c
(
n
)
t
−
DP c
1
. The negative value of ∆
DP c
(
n
)
t
is
−
−
−
(
n
)
t−
−
not allowed.
DP c
−
(
n
)
t
its self is
R
t
−
De
t−
1
. The water infiltrate will enter
(
DP c
t−
1
Ks
−
1
)) top layer is
>
1. It means that, all
of soil pores in each layer had been filled by water and saturate when depth
of water percolation is equal to
Ks
.
−
to second layer if (1
3. Soil Water Content Fluctuation and Water Depletion
Table 1 shows a general ∆
θ
in soil layer from dry to wet pattern. In order
to model requested the initial SWD, a fluctuation of
θ
between losses (
−
1)
and gain water (+1) in three soil profiles are proposed.
In order to elaborate an important factor which has effect toward SWD
significantly such as a climate, crop type, and Andosol soil parameters from
