Environmental Engineering Reference
In-Depth Information
During the first period of 10 days the equilibrium sediment concen-
tration is larger than the incoming, actual sediment load, in terms of time
as well as space, for the rotational and for the continuous flow. In the
second and third period the incoming sediment load is larger in a few
canal reaches than the equilibrium concentration for the rotational flow,
especially in the reach DE. In this reach sediment will be deposited with
a maximum height of about 5 cm. In Period 4 the actual sediment load
is smaller than the equilibrium concentration and the already deposited
sediment during the periods 2 and 3 will be eroded and transported out
of the canal. During Period 5 the equilibrium concentration is larger than
the incoming load, but no sediment will be picked up due to the fact that
the original bottom level was reached at the end of Period 4.
The sediment behaviour for continuous flow is comparable with that
for the rotational flow during periods 1, 2 and 3. However, during
periods 4 and 5 the incoming load is relatively larger than the equilib-
rium concentration and the deposition of sediment will continue during
periods 4 and 5, resulting in about 700 m 3
sediment being deposited
in the canal.
Figure 7.23 shows the total volume of deposition in the canal for
respectively continuous and rotational flow at the end of each period and
for a sediment inflow that changes with the incoming discharge as given
in Table 7.10.
700
600
500
400
300
200
100
0
Figure 7.23. Sediment
deposition in the canal network
as a function of time for
continuous and rotational flow
according to Ackers-White.
5
10
15
20
25
30
35
40
45
50
0
Time (day)
Rotational flow
Continous flow
Table 7.10.
Incoming sediment concentration during the irrigation season.
Irrigation period of 10 days
Period
1
2
3
4
5
Sediment concentration (ppm)
200
300
200
300
200
 
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