Environmental Engineering Reference
In-Depth Information
Table 7.7.
Main characteristics of the main irrigation canal.
Reach
AB
BC
CD
DE
EF
Offtake number
1
2
3
4
5
6
Location from headworks (km)
3
6
10
12
16
16
Command area (ha)
1 800
1 600
1 500
1 600
1 800
1 700
Table 7.8.
Geometrical data of the main irrigation canal ABCDEF.
Chézy's
Bottom
Normal
Length
L
Width
B
roughness
Side slope
slope
water
S
o
(10
−
3
)
Reach
(m)
(m)
coefficient
m
(-)
depth (m)
A-B
3 000
5.15
42
1.5
0.345
1.19
B-C
3 000
5.15
42
1.5
0.345
1.19
C-D
4 000
4.00
42
1.5
0.375
1.04
D-E
2 000
4.00
42
1.5
0.375
1.04
E-F
4 000
2.70
42
1.5
0.425
0.83
Table 7.9. Water needs during the irrigation season of the irrigated area.
Irrigation period of 10 days during the irrigation season
Period
1
2
3
4
5
l/s
·
ha
6
5
4
6
5
Table 7.7 shows the main characteristics and Table 7.8 gives the
geometrical and hydraulic characteristics of the main canal.
The whole irrigation season is divided into 5 periods of 10 days.
Table 7.9 gives the water requirement at the headworks for each period.
For the simulation of the effects of the operation plan on the sedi-
ment deposition in the main canal, a few scenarios are analysed. All of
them comply with the water requirements and the water supply for the
irrigated areas. The Ackers-White sediment transport predictor is used
to compute the sediment transport capacity. In this hypothetical case
the distribution efficiency of the main canal is assumed to be 100%.
The incoming sediment load at the headworks during the whole irrigation
season is characterized by a median diameter
d
50
of 0.15 mm. The
incoming sediment concentration varies per period of 10 days.
The scenarios are:
•
Scenario 1 (continuous flow)
: a continuous flow to all offtakes during
the whole season (see Figure 7.21);
•
Scenario 2 (rotational flow by 5 days)
: a rotational flow during a period
of 10 days towards the groups A and B; each group receives water for
alternate periods of 5 days.
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