important terms in irrigation

1. DEFINITIONS OF SOME COMMON
IMPORTANT TERMS

2.  Base Period or Base (B)
 It is the whole period of cultivation from the time
when the irrigation water is first issued for
preparation of the ground for planning the crop, to
it’s last watering before harvesting
 It is the period in days during which flow is
continued for a particular crop.

3.  Crop period :
It is the time in days that a crop takes from
the instant of its sowing to that of its
harvesting.

4.  Duty (D)
 It is the total area irrigated by a unit discharge running
continuously during the base period and its unit is
area/cumec.
 It is irrigating capacity of a unit of water.
 Thus, duty gives the relationship between the
volume of water and area of the crop
 E.g. 3 cumecs of water is required for a crop sown in an area
5100 hectares.

5.  Duty of irrigation water will be 5100/3=1700
hectares / cu-mec,
 And the discharge of 3 cu-mecs is required
throughout the base period

6.  Delta (∆)
 It is total depth of water required by a crop
during the entire period the crop is in the field
and is denoted by symbol ∆
 E.g.crop required about 12 waterings, then
the delta for that crop =12x10=120cm=1.20 m

7.  If the area under the crop is A hectares, total
quantity will be 12 x 10= 120 cm = 1.2 m
 Total quantity will be 1.2 A hec meters in a
period of 120 days.

8. Relation between Duty (D),
and Delta (∆)
 Let D= duty in hectares/ cumec
 ∆ = total depth of water supplied (in m)
 B= base period in days.
 i) If we take a field of area D hectares, water supplied to
the field corresponding to the water depth ∆ meters will
be = ∆ x D hec-m
 = D X ∆ X 104 cubic-meters ………..(1)

9.  Ii) again the same field of D hectares, one
cumec of water is required to flow during the
entire base period. Hence , water supplied to
the field
 = (1) x (B X 24X 60 X 60) m3 ……………………(2)

10.  Equating (1) and (2)
 DX ∆ X 104 = B X 24X60X60
 OR
 ∆ = B X 24X60X60 / DX 104
 = 8.64 B/D meters.

11. Gross Command Area (GCA)
 An area is usually divided in to a number of water sheds
and drainage vallys
 The canal usually runs on water shed and water can flow
from it on both sides, due to gravitational action only up
to drainage boundaries
 Thus in a particular area lying under the canal system ,
the irrigation can be done only up to drainage boundaries

12.  The gross commanded area is thus the total
area lying between drainage boundaries
which can be commanded or irrigated by
canal system.

13. Culturable Command Area (CCA)
 The gross commanded area also contains unfertile barren
land, alkaline soil, local ponds, village and other areas as
habitation.
 These areas are known as un-culturable areas
 Remaining area on which crops can be grown
satisfactorily.
 Is known as CCA
 GCA = CCA + un-culturable area

14.  Culturable command area can be classified as
 Culturable cultivated area and culturable
uncultivated area.

15. Intensity of irrigation
 Intensity of irrigation is defined as the percentage of
culturable commanded area proposed to be irrigated
during either a crop season or during a year
 E.g. if CCA of an irrigation field is 120hectares
 Out of which 90 hectares of land is cultivated during
kharif season and 60hectares of the land is cultivated
during rabbi season

16.  The intensity of irrigation during kharif season will be =
(90/120)100=75%
 and the intensity of irrigation during rabbi crop will be (60/120)
x 100=50%
 However the yearly intensity of irrigation will be equal to the
sum of the two i.e.75+50=120%
 Thus yearly intensity of irrigation can be more than 100%

17. Factors affecting duty
 Methods and system of irrigation
 Mode of applying water to the crops
 Method of cultivation
 Time and frequency of tilling
 Type of the crop
 Base period of the crop
 Climatic conditions of the area
 Quality of water
 Methods of assessment of irrigation method
 Canal conditions

18.  Character of soil and sub soil of the canal
 Character of soil and sub soil of irrigation
fields

19. Methods of improving duty
 Suitable methods of applying water to the crops
should be used
 The land should be properly ploughed and levelled
before sowing the crop
 It should be given good tilth
 The land should be cultivated frequently as it reduces
loss of moisture
 Canal should be lined and water can conveyed quickly
to reduce evaporation loss

20. Methods of improving duty
 Parallel canal should be constructed to reduce losses
and to maintain level
 The alignment of canal either in sandy soil or in
fissured rock should be avoided
 The canal should be so aligned that areas to be
cultivated are concentrated along it
 The source of supply should be such that it gives good
quality of water
 The rotation of crops must be practiced

21.  Volumetric method of assessment should be used
 The farmers must be trained in the proper use of water so that
they apply correct quantity of water at correct timing
 The land should be redistributed to the farmers so that they get
only as much land as they are capable of managing it
 Research stations should be established in various localities to
study soil etc.

22.  The canal administrative staff should be
efficient , responsible and honest so that
farmer at head and tail of canal should get
equal quantity of water

23. Definations
 KOR PERIOD AND KOR DEPTH
 The distribution of water during the base
period is not uniform
 Crops require maximum water during first
watering