Water technology and Sciences November-December 2013 - page 100

98
Water
Technology and Sciences. V
ol. IV, No. 5, November-December, 2013
Saucedo
et al.
,
Optimal Volume Flow for Border Irrigation when a Shallow Water Table is Present
5 000
4 500
4 000
3 500
3 000
2 500
2 000
1 500
1 000
500
0
Distance (cm)
Time (s)
0 2 000 4 000 6 000 8 000 10 000 12 000
Figure 1. Calibration of the Model;
ψ
d
= -15 cm and
k
s
= 1.86 cm/h,
R
2
= 0.9984.
(CUC):
CUC
=
1 1
/ n ˆI
(
)
I
i
ˆI
i
=
1
n
, where
I
i
is the
infiltration lamina at point
I
[
L
] and
n
is the
number of points used for the calculation.
Figure 3 shows the relationship between the
optimal flow and the border length for which it
is calculated. This flow is described sufficiently
well by a linear correspondence. The figure
was generated for an irrigation lamina of 10
cm, but the behavior is similar regardless of the
irrigation lamina to be applied. The result is
similar to that obtained for the case in which no
water table is present in the soil profile, which
indicates that the mainly linear correspondence
between border length and optimal irrigation
flow is independent of the initial distribution of
the pressures in the soil. As an example, Figure
4 shows the final distribution of the infiltration
lamina for an irrigation lamina of 10 cm and a
water table depth of 100 cm for La Chontalpa
clay soil. This depth has been used to define
the initial distribution of pressures in the soil
according to equation (11).
Design Table for Border Irrigation for
Clay Soil with the Presence of a Water
Table
Table 1 shows the unit flow values, that is,
the flow to be applied per unit border width
and per unit border length, corresponding to
different irrigation laminas and initial water
table depths. The empty boxes indicate that the
desired amount of water to be applied is greater
than the amount of water that can infiltrate
into the soil. Table 2 shows the irrigation
times corresponding to the unit flows shown
in Table 1. With initial positions of the water
table of 100, 150, 200 and 10 000 cm, the optimal
flow increases as the depth of the water table
increases. Since the depths considered are not
in the asymptotic zone of the moisture retention
curve, which extends from the water table to
the soil surface as a result of the distribution of
the hydrostatic pressures adopted, the expected
asymptotic behavior of the optimal irrigation
flow cannot be attained. Nevertheless, the
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