Hydraulic controls on primary canals

As the small cultivator is not generally involved in operations at the primary canal level, technical details of primary canal control structures are not relevant to this discussion. However, the extent to which irrigation systems are designed to be demand-responsive at the tertiary level has a major influence on the operational requirements of primary canal controls.

With currently available technology it would be technically possible to make primary canals instantly responsive to changes in demand. It would, however, be very costly to do so and unjustified when problems in management of limited-demand at the small cultivator level, discussed earlier, rule out such operation at least for the immediate future.

Of more immediate concern is the need to design into the primary system controls which can accommodate possible future developments, such as a change in the direction of greater crop specialization in various areas of the project command, with consequent changes in allocation of water to particular secondaries and in capacity required at structures. The possibility of a future change from on/off full flow rotation of secondaries in favor of continuous regulated flow, which could affect design requirements of outlet structures on the primary canal, should also be taken into account (Plusquellec 1985 and 1988, Le Moigne 1988).