Duty :

The term duty means the area of land that can be irrigated with unit volume of irrigation water. Duty represents the irrigating capacity of a unit.

It is the relation the between the area of a crop irrigated and the quantity of irrigation water required during the entire period of the growth of that crop.

For example, if 3 cumecs of water supply is required for a crop sown in an area of 5100 hectares, the duty of irrigation water will be 5100/3 = 1700 hectares/cumecs, and the discharge of 3 cumecs will be required throughout the base period.

Variation of duty with the place of its measurement

• By the number of hectare that one cumec of water can be irrigated during the base period, i.e. 1700 hectares/cumec.
• By the total depth of water (or Delta), i.e. 120 metres
• By the number of hectare that can be irrigated by a million cubic metre of stored water. This system is used for tank irrigation.
• By the number of hectare metre expended per hectare irrigated. This is also used in tank irrigation