Environmental Engineering Reference
In-Depth Information
The canal design methods as discussed above do not directly use avail-
able information on sediment characteristics, such as sediment size and
concentration. Nowadays the design of irrigation canals is the product of
complex and difficult to determine parameters such as water flow, required
water levels, sediment load, structure control and operation and manage-
ment strategies. No design packages are available that deal with all these
parameters at the same time. When analyzing one parameter, others are
either ignored or assumed to be constant. Therefore, it is obvious that a
mathematical model for the specific conditions of irrigation canals will
be an important tool for designers and managers of irrigation systems.
4.4 APPURTENANT CANAL STRUCTURES
4.4.1 Irrigation structures
The conveyance of irrigation water from the head works to the farmer's
field can be realized by an open irrigation network that consists of canals
with a large number of appurtenant structures; the latter can be divided
into a conveyance and an operational part. The conveyance part includes
the canals and structures that convey, regulate, measure and divide the
water flow. The operational part consists of the structures that divide and
control the flow in terms of water level and/or discharge; they may be
without any movable part (fixed) or they have movable parts such as gates
for the control.
The main objectives of an irrigation network are to deliver irrigation
water:
in the right quantity (in size, frequency and duration);
at the required level (head);
at the right place;
at the right moment;
equitably (fairly and objectively);
in a reliable and assured way.
To meet these objectives the structures will have to regulate, control,
measure or distribute the water flow (Leliavsky, 1983). The design of the
conveyance part is normally based on hydraulic and structural require-
ments, local conditions, available technology and cost. The operational
part includes additional structures that support the operation and manage-
ment for the water delivery mode, acceptance by the water users, ease in
operation, transparency, etc. The sediment transport aspect is normally not
considered in the selection and design of canal structures. An irrigation
system can comprise the following structures:
head works at the head of a primary or main canal: a weir or barrage,
free intake, reservoir, pumping station;
conveyance structures: aqueducts, chutes, closed canals, culverts, drop
structures, flumes, inverted siphons, siphons, tunnels;
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