Environmental Engineering Reference
In-Depth Information
The change is given by:
c
1
Q
1
c
i
Q
i
Q
2
c
2
=
Q
2
+
(6.12)
where:
c
1
=
sediment concentration in the canal upstream of the inflow (ppm)
c
2
=
sediment concentration after the inlet (ppm)
c
i
=
concentration of inflow (ppm)
discharge before the inlet (m
3
/s)
Q
1
=
inflow discharge (m
3
/s)
Q
i
=
discharge after the inlet (m
3
/s)
Q
2
=
For an outflow the continuity for the water flow gives
Q
1
=
Q
2
+
Q
i
and the sediment concentration after the offtake point is given by:
c
1
Q
1
(
Q
2
+
c
2
=
(6.13)
f
d
∗
Q
o
)
where:
Q
1
=
discharge before the offtake (m
3
/s)
offtake discharge (m
3
/s)
Q
o
=
f
d
=
=
sediment distribution ratio at the offtake
c
o
/c
2
Irrigation aspects
- The model of the irrigation network can be most simply composed of
a main canal and secondary canals with tertiary outlets. Each canal is
divided into several reaches or sections;
- The model can include changes in the bottom level at the upstream
boundary of a canal section;
- Control sections can be set at the downstream end of the main canal
or secondary canals. The type of structure located at the downstream
end of a section sets the water level, both for upstream and downstream
control: the first one sets the upstream water level and the other the
downstream water level;
- The network might include lateral inflow or outflow; these lateral flows
should be located at the end of a canal section for upstream con-
trolled systems and at the downstream side of the gate for downstream
controlled irrigation systems;
- The flow control structures that can be incorporated include:
•
overflow type
: crest width, crest level;
•
undershot type
: width and height of the rectangular opening;
•
submerged culverts and inverted siphons
: number and diameter of
pipes;
•
flumes
: the upstream head-discharge relationship;
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