Different Methods of Expressing Duty
1. By the number of hectares that one cusec of water can irrigate during the base period. i.e.,
1000 hectares/cusecs.
2. By the total depth of water or delta.
3. By number of hectares that can be irrigated by a million cubic meter of stored water, this
system is used for tank irrigation.
4. By the number of hectare meter expended per hectare of area irrigated. This also used in
tank irrigation.
Relation between Duty, Delta and Base Period
Let ‘D’ be the duty of water in hectares/cusec.
‘B’ be the base period in no. of days.
'∆’ be the depth of water required in meters.
1 cusec of water flowing for a base period of ‘B’ days provides a volume of water equal to
1×60×60×24×B cubic meters.
Quantity of water in ‘cm’ required for flooding 1 hectare (1000 sq.m) of area with a depth of ‘∆’
meters= 1×1000×∆ cubic meters.
❖ No. of hectares that can be irrigated by 1 cusec of water flowing for ‘B’ days.
= 1×60×60×24×B
1×10,000×∆
= 86400×B = 8.64 B
10000×∆ ∆
Hence D = 8.64 B
∆
Factors of Effecting Duty
The factors which govern the duty of canal water are:
1. Rainfall: if the amount of rainfall is more during the base period of a crop the water required
will be less and the duty is high.
2. Evaporation: If the temperature prevailing in the area is high the loss due evaporation is
more and the duty will be low.
3. Base Period of Crop: If the base period is small then the quantity of water required is less
and so duty will be high.
4. Soil Characteristics: Soils of close grain hold more water due to more no. of voids than sandy
soils, so duty in the case of close-grained soils will be more compared to sandy soils.
1. By the number of hectares that one cusec of water can irrigate during the base period. i.e.,
1000 hectares/cusecs.
2. By the total depth of water or delta.
3. By number of hectares that can be irrigated by a million cubic meter of stored water, this
system is used for tank irrigation.
4. By the number of hectare meter expended per hectare of area irrigated. This also used in
tank irrigation.
Relation between Duty, Delta and Base Period
Let ‘D’ be the duty of water in hectares/cusec.
‘B’ be the base period in no. of days.
'∆’ be the depth of water required in meters.
1 cusec of water flowing for a base period of ‘B’ days provides a volume of water equal to
1×60×60×24×B cubic meters.
Quantity of water in ‘cm’ required for flooding 1 hectare (1000 sq.m) of area with a depth of ‘∆’
meters= 1×1000×∆ cubic meters.
❖ No. of hectares that can be irrigated by 1 cusec of water flowing for ‘B’ days.
= 1×60×60×24×B
1×10,000×∆
= 86400×B = 8.64 B
10000×∆ ∆
Hence D = 8.64 B
∆
Factors of Effecting Duty
The factors which govern the duty of canal water are:
1. Rainfall: if the amount of rainfall is more during the base period of a crop the water required
will be less and the duty is high.
2. Evaporation: If the temperature prevailing in the area is high the loss due evaporation is
more and the duty will be low.
3. Base Period of Crop: If the base period is small then the quantity of water required is less
and so duty will be high.
4. Soil Characteristics: Soils of close grain hold more water due to more no. of voids than sandy
soils, so duty in the case of close-grained soils will be more compared to sandy soils.
