Contents preface (VII) introduction 1—37

5.11. DELIVERY OF WATER TO FARMS
Once water has been brought to the watercourse, the problem of its equitable distribution amongst the farms located along the watercourse arises. There are the following two possible alternatives (4), each with its own merit, for achieving this objective:
(i) Restrict the canal irrigation to such limited areas as can be fully supported with the lowest available supply. This does not lead to the total utilisation of available water. Agricultural production and protection against famine would also not be optimum. The production would be maximum per unit of land covered though not per unit of water available. It would, however, not require a precise or sophisticated method for the distribution of irrigation water. The delivery system for this alternative can be either continuous or demand-based, depending upon the availability of water. A continuous delivery system can be effectively used for large farms and continuously terraced rice fields. Though ideal, a demand-based delivery system is not practical on large irrigation systems.
(ii) Extend irrigation to a much larger area than could be supported by the lowest available supply. This creates perpetual scarcity of irrigation water but ensures that a comparatively less quantity of water remains unutilised. Agricultural

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production and the protection against famine would be at the optimum levels. The production would be maximum per unit of available water though not per unit of land covered. This method would have greater social appeal, and requires precise and sophisticated methods for equitable distribution of irrigation water.

Irrigation water from a distributary can possibly be delivered to farmers in the following four different ways:
(i) Continuous delivery system (ii) Free demand system

(iii) Rotation delivery system

(iv) Controlled demand (or modified rotation) system.
In the continuous delivery system water is supplied continuously to the farm at a predetermined rate. This system is easy to operate, but would generally result in excessive water applications. This delivery system can be efficient only if the farms are so large that the farmer can redistribute his supply at the farm to different pockets of his farm in accordance with crop and soil conditions. This may necessitate regulatory storage at the farm for efficient utilization of the water delivered to the farm. Large corporation farms or state-owned farms can be served efficiently by this system.
In a free demand system, farmers take intermittent delivery at will, depending upon the needs of their crops, from the constantly available supply in such a manner that their instantaneous withdrawal rate does not exceed that for which they subscribe and which also corresponds, in some way to the installed capacity. Obviously, this system provides maximum flexibility but requires that the farmer is closely aware of crop irrigation requirement and does not have tendency to overirrigate when water is not sold by volume. This system also leads to uncontrolled peak demands during daylight hours and excessive operational losses during night. The day-time peak demands may require large delivery capabilities. Free demand system is well adapted to well irrigation rather than canal irrigation.
In the rotation delivery system the canal authority assumes responsibility for allocating the continuous flow available in the relevant distributary to each farmer of the area which is served by the distributary. The farmers get water according to a fixed delivery schedule. This method is capable of achieving equitable distribution to a large number of farmers with relatively lesser water supplies. Hence, this method is generally adopted for canal irrigation supplies in India and is known by the name of ‘warabandi’ in India and has been described in greater detail in the next article.
Obligatory use of water supplied to the farm may cause considerable wastage of water and result in waterlogging without increasing the production. On the other hand, failure to adjust rotation schedules to crop irrigation requirements may result in inefficient irrigation during crucial growth periods and thus affect adversely the crop production. To overcome the deficiency of the rotation delivery method, water may, alternately, be delivered according to some kind of controlled demand system which is a sort of compromise between free demand and rotation delivery systems. In this modified system of modified rotation, priority for delivery is on a rotation basis, but actual delivery may deviate depending upon the actual demand. Obviously, much better coordination between farmers and the authorities would be required for this system to work efficiently.