Contents preface (VII) introduction 1—37

6.4.7. Main System Management

Operational management of the main system refers to management aspects of the future allocation, scheduling, delivery of water on main systems down to and including outlets, and

234 IRRIGATION AND WATER RESOURCES ENGINEERING
the disposal of water in drains below chaks (i.e., the irrigated fields) (1). It includes planning, decision making, the operation of controls, and communications both upwards to managers and downwards to groups of farmers so that equitable supplies can be ensured throughout the command area (1). Main system management (MSM) is capable of reducing gross inequities of water supply to tail-end farmers and increasing the farm yield from the command area. A suitable type of MSM can induce the farmers for active involvement in on-farm development and maintenance and adoption of high-yielding practices. The importance of MSM is more in reservoir-based irrigation systems than in the systems based on diversion schemes because of the available options of storage and release.
According to the present system of operation, the main canal and branches run continuously with either full or reduced supply depending on the availability of water. The distributaries and minors, however, run intermittently in accordance with the keenness of demand as assessed by the concerned field staff. Such assessment tends to be subjective as well as approximate. A more rational method for the running schedule of distributaries and minors can, alternatively, be worked out as follows (8):
(i) Obtain the cropping pattern, preferably an optimum one, for irrigation during the ensuing season,
(ii) Estimate weekly evaportranspiration and corresponding effective rainfall based on past records,
(iii) Determine the irrigation demand,
(iv) Decide upon the amount of canal water and ground water to meet the irrigation demand such that the desired intensity of irrigation on the optimum cropping pat-tern can be obtained along with a stable water table, and
(v) Prepare a roster of regulation of distributaries and minors and notify the concerned farmers well in advance to enable them to plan their sowing and irrigation pro-grammes accordingly.
Provision for departure from the notified roster should be available. Such departures should be made only if there is variation in rainfall pattern.