This presentation contains some of the factors affecting the duty of irrigation water and also the measures to improve the duty. Hope this will found very helpful to you...

1. Factors affecting Duty and
Improvement Measures
L.D. College of Engineering, Ahmedabad-15

2. Page  2
Group members:
Sr. No. Name Enrollment No.
1. Patel Pranjal 130280106086
2. Patel Vaibhav 130280106088
3. Patel Vedant 130280106089
4. Patel Vishesh 130280106090
5. Patni Mo.Aamir 130280106091

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Content
Introduction
Factors affecting duty
Measures to improve duty
References

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Introduction
The term “Duty” means the area of land that can be irrigated with unit volume of
irrigation water.
Quantitatively, duty is defined as the area of land expressed in hectares that can be
irrigated with unit discharge, that is, 1 cumec flowing throughout the base period,
expressed in days.
Imagine a field growing a single crop having a base period B days and a delta ∆ mm
which is being supplied by a source located at the head (uppermost point) of the field,
as shown in next slide.

5. Page  5
Introduction (cont..)
[Border Irrigation method of applying water]
[Furrow Irrigation
method of applying
water]
[Water
applied to
field by
pumping
ground water]

6. Page  6
Introduction (cont..)
If the water supplied is just enough to raise the crop within D hectares of the field,
then a relationship may be found out amongst all the variables as:
Volume of water supplied = B*60*60*24 cum
Area of crop irrigated = D*10000 sqm
Hence, knowing two of the three variables B, D and ∆ the third party may be found
out.
Volume of water supplied per unit area = =
86400B
10000D
8.64B
D

7. Page  7
Factors affecting Duty
Coarse grained
soil
Percolation
losses are high Low duty
Fine grained
soil
Percolation
losses are less High duty
Type
of soil

8. Page  8
Factors affecting Duty (cont..)
Crop A
Large quantity
of water Low duty
Crop B
Less quantity of
water High duty
Type
of crop

9. Page  9
Factors affecting Duty (cont..)
Good structure
Evaporation
losses are less High duty
Good structure
Properly
aerated
because of
large voids
Yield of
crop
increases
Structure
of Soil
Good structure is called Good Tilth of Soil

10. Page  10
Factors affecting Duty (cont..)
Steep slope
d/s portion
get more
water
u/s portion
remain drier
Low
duty
Flat slope
u/s portion
remain drier
d/s portion
get more
water
Low
duty
Slope of
Ground
Properly
prepared field
Equal
distribution of
water
High duty

11. Page  11
Factors affecting Duty (cont..)
Temperature and
wind velocity are
high
more evaporation
losses Low duty
Rainfall during
base period
Less irrigation
requirement High duty
Climatic
Conditions

12. Page  12
Factors affecting Duty (cont..)
Properly ploughed &
made quite loose
water retention
capacity increase
number of watering
reduced High duty
Not properly ploughed
& method of cultivation
is faulty & less efficient
Low duty
Method of
Cultivation

13. Page  13
Factors affecting Duty (cont..)
Perennial
Water
application
throughout
the growth
period
soil remains
continuously
wet
less quantity
of water
High
duty
Non-perennial
Only during
flood season
wasteful use
of water Low duty
System
of
Irrigation

14. Page  14
Factors affecting Duty (cont..)
Tank Irrigation
Command area
closed to tank
Transmission
losses are less High duty
Canal Irrigation
Command area
far from source
Transmission
losses are
more
Low duty
System
of
Irrigation

15. Page  15
Factors affecting Duty (cont..)
Lift Irrigation
Command area
close to well
More expensive High duty
Flow Irrigation
Command area
far from source
Less expensive Low duty
System
of
Irrigation

16. Page  16
Factors affecting Duty (cont..)
Drip Irrigation Most efficient Very high
duty
Sprinkler
Irrigation
Seepage losses
are reduced High duty
Application
of Water
Surface
irrigation
More waste of
water Low duty
Duty of subsurface methods > Duty of surface methods

17. Page  17
Factors affecting Duty (cont..)
Initial stages of
cultivation
land not
properly
levelled
Low duty
Age of
cultivation
increases
Slope and
condition of
land improve
with age
High duty
Age and
frequency
of
cultivation
Frequent
cultivation
Reduces loss of
moisture High duty
Cultivation after
long interval
More loss of
moisture Low duty

18. Page  18
Factors affecting Duty (cont..)
Canal A
In good
condition &
properly
maintained
High duty
Canal B
In unconcerned
condition & not
maintained
Low duty
Condition,
type and
location of
Canal
Canal A
Located in
middle of
command
area
Losses are
small
High
duty
Canal B
Located
away from
command
area
Losses are
more
Low
duty
Duty of Lined canal > duty of unlined canal
Duty of canal in alluvial soil > duty of canal in non-alluvial soil

19. Page  19
Factors affecting Duty (cont..)
Flat rate based
assessment
Wastage is more Low duty
Volumetric
assessment
Cultivators use
water carefully
Less wastage High duty
Method of
assessment
of Water
Skill of
Cultivators
Cultivators
Skilled & properly
trained
Make judicious
use of water High duty

20. Page  20
Factors affecting Duty (cont..)
Long base period
More water
required Low dutyBase period
Soil Content
Soil
Contains harmful
salts and alkalis
More water
required for
leaching of salts
Low duty
However it is not always proportional

21. Page  21
Measures for Improvement of Duty
Land should be properly ploughed
Land should be regularly cultivated
Canal alignment in sandy soils or in fissured rocks should be avoided
Canal should be located in the middle of command area
Canal should be lined
Canal should be properly maintained
Efficient methods of irrigation should be adopted

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Measures for Improvement of Duty (cont..)
Volumetric assessment of water should be adopted
Cultivators should be trained
System of rotation of crops should be adopted
Canal alignment through soil containing harmful salts should be
avoided
Instead of a single big canal, two or more parallel canals of small size
should be preferred
Adopt modern methods of irrigation instead of conventional methods
Cultivators at all levels of canal should get the sufficient quantity of
water when needed

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References
Dr. K. R. Arora (Reprint 2013) Irrigation, Water Power and Water Resource
Engineering, Standard Publishers Distributers, Delhi
Internet content

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