Environmental Engineering Reference
In-Depth Information
0.90
0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0
0.60
Figure 7.27. Relative deposition
in the canal upstream of a weir
with various widths and as a
function of the relative
discharge.
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.0
Relative discharge
B = 12 m
B = 7 m
B = 10 m
B = 6 m
B = 8 m
B = Gate flow 8 m
0.90
0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.10
Figure 7.28. Relative deposition
in the canal for various crest
levels.
0
10.8
10.9
11.0
11.1
11.2
11.3
11.4
11.5
11.6
11.7
11.8
Weir crest
The incoming concentration equals the equilibrium concentration for the
design crest height (55 ppm). The design crest level is
10.90 m above
datum and no sedimentation in the canal is observed for this 10 m-wide
weir. For higher weir crests the relative sediment deposition increases
relatively sharply and above a certain level the relative deposition
levels off (see Figure 7.28).
The relative deposition has a steep rise in the beginning and flattens
off for higher crest levels. For the design discharge and an inflow concen-
tration less than the equilibrium concentration, there is no deposition. For
a crest height higher than the design level a backwater profile is created
that will reduce the sediment transport capacity in the canal and deposi-
tion will take place. For higher crest levels more deposition will take place
in the system and sediment flowing out of the system will decrease. At a
certain crest level most of the inflowing sediment is deposited in the sys-
tem, the concentration near the weir becomes low (1-2 ppm) and further
increments of the crest level will not result in any quantifiable increase
+
 
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