Design Criteria for Irrigation Canals - Sediment Transport in Irrigation Canals: A New Approach - page 60

Set point

Negative dynamic storage Set point

Off-take

Off-take

Figure 4.2. Upstream control.

4.2.2 Downstream control
Downstream control systems respond to water level changes downstream
of a regulator. The structures permit instantaneous response to changes
in demand by using the storage in the upstream canal section (positive
dynamic storage) in the case of an increase in demand and by storage of
water in the case of a decreasing demand. Downstream control systems can
be manually operated, but they are easily automated, either hydraulically
(Neyrpic) or electrically. AVIS and AVIO are examples of automatic gates
that react to the water level at the downstream side (Ankum, 2004).
Both water level and flow are controlled at the upstream end of a canal
section (Figure 4.3). Changes are gradually passed on in the upstream
direction towards the head works. Most downstream control systems
use balanced gates. These control systems are specifically designed to
maximize flexibility by minimizing the system response time.

Set point

Positive dynamic storage

Set point

Off-take

Off-take

Figure 4.3. Downstream

control.

The application of downstream control is usually limited to canals with
a bed slope smaller than 0.3‰. Downstream control can be applied both in
on-demand and on-request delivery systems. The main design requirement
is that each canal section has sufficient capacity to meet the maximum
instantaneous demand. Downstream control is also a serial process.

4.3 THE ROLE OF SEDIMENT TRANSPORT IN THE DESIGN
OF IRRIGATION CANALS

The design of irrigation canals for sediment-laden water should consider
aspects related to the conveyance of irrigation water as well as the transport