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close this book Using water efficiently - Technological options
close this folder Water use efficiency
View the document What efficiency are we talking about?
View the document What are current levels of water use efficiency in irrigation?
View the document Factors affecting irrigation water use efficiency
View the document Water use efficiency in the urban sector: Definitions
View the document Factors affecting urban water use efficiency: Examples

What are current levels of water use efficiency in irrigation?

DEFINITIONS. In irrigation, the delivery of water from water sources to field crops depends on the efficiency in three main levels of an irrigation system: conveyance, distribution, and field (on farm) application (Bos: 1983; 1990). Figure 1 illustrates the framework of analysis for a typical irrigation system.


Figure 1 An Irrigation Framework

i. Conveyance is the movement of water from its sources (reservoirs, river diversions, wells or pumping stations) through main and secondary canals to the tertiary offtake of a distribution system. Conveyance efficiency, Ec, is defined as:

Ec = Vd/Vs. where: Vs = volume diverted from sources plus inflows to the canal from other sources; Vd = volume delivered to the distribution system.

ii. Distribution is the movement of water from tertiary and distribution canals, channels or pipes to individual field inlets. Distribution efficiency, Ed, is defined as:

Ed = Vf/Vd. where: Vf = volume furnished to the field.

Often, the combined efficiency of a conveyance and distribution system is described as irrigation network efficiency, En. It is defined as the water delivered to farm field inlets divided by the water diverted from the prime source:

En = Vf/Vs = Ec x Ed.

iii. Field application is the movement of water from field inlets to crops. The field (or on-farm) efficiency, Ef, is defined as:

Ef = Vm/Vf. where: Vm = net volume needed to maintain the soil moisture, which is equal to the amount consumptively needed for evapo-transpiration, i.e. Vm = (crop water requirement) - (effective rainfall).

Another concept widely used in irrigation is the overall or project efficiency, Eo. It is the ratio between the quantity of water consumptively used by crops and the total water diverted from the sources to a project area. It encompasses seepage and evaporation losses incurred in physically conveying water to crops, as well as losses due to deep percolation through the root zone to groundwater and field runoff.

Eo = Vm/Vs = Ef x Ec x Ed.

Finally, irrigation sector efficiency, Ei, is defined as the amount of water actually consumed by the sector divided by the amount of water made available for the sector of a country.

EXAMPLES. Examples of WUE at different levels and project areas in selected countries are presented in Table 3 (a, b, c, d), incorporating data from several sources. Later sections of this paper present a detailed analysis of the figures in Table 3. An overview comparing water use efficiencies between the developing countries and the United States is presented below

On average, the network efficiency, En, for developing countries has been estimated at 68 percent. Most countries show a range of 60-75 percent. The average En in the United States is estimated at 78 percent. According to the sources reviewed for this study, the on-farm efficiency, Ef, varies from 40-85 percent. In the United States, the Ef in the intensively developed areas ranges from 50-85 percent, with a national average of 53 percent. The average Ef in developing countries is around 40 percent. The overall efficiency Eo, encompasses losses from conveyance, distribution and field application, and therefore varies widely. The Eo of many systems can be as low as 20 percent, such as in Yemen. Well-managed systems show efficiencies of 50 percent or more, such as in Cyprus. The average for developing countries is 30 percent. For pipe delivery systems in the United States, Eo varies from 30-80 percent, with a national average of 41 percent. Most cases cited in Table 3 show an Eo of less than 40 percent, except for Cyprus, Jordan and the two project areas in Doukkala in Morocco. All three cases, which have Eo values of more than 40 percent, reflect the impact of sprinkler, drip and advanced water control technologies. In Cyprus, for example, all irrigation water supplies in the public irrigation systems as well as all groundwater extractions are metered. This accounts for the high efficiency level. There is suggestive evidence that an overall efficiency of 45-55 percent may be a ceiling for a gravity system in the cultivation of non-paddy crops.

Table 3 Irrigation Water Use Efficiencies at Various Levels

Table 3a Network Level

Countrv

(%)

Specification

Cyprus

95

Pipe conveyance systems with sprinkler and drip

U.S.

78

Average

France

75-85

Bas-Rhone region, main canal 100% lined

Jordan

75

Open canals with manual control, on-farm sprinkler/drip storage &

Morocco

74

Doukkala project with sprinkler system

Morocco

72

Doukkala project with gravity system

Morocco

70

Open canal systems with hydraulic irrigation control & surface

West Bank & Gaza

74

Ec=87%, Ed=80-90% for distribution wells system of artesian

Dev.g countries

68

Average

Egypt

67

Ec=75 % and Ed=89%b

Mexico

67

Sinaloa project

Colombia

65

Coello project.

Mexico

61

Yaqui project.

Syria

60

Most schemes at 60% with upper limit of 75%b

Turkey

60

Traditional open canal systems with manual controld

Kyrghyzstan

55

poor cosign, built and maintenance of distribution canals'

Mexico

54

Panuco project

Yemen

50

Large-scale spate irrigationd

Pakistan

45-60

Ec=75% and Ed=60-80%b

Table 3b On-farm Level

Country

(%)

Specification

East India

85

Rico irrigation on shallow soils over hard-rock areas.

Israel

75-80

nearly 100% by sprinkler irrigationb

Cyprus

70

Pipe conveyance systems with sprinkler and dripd

Jordan

70

Open canals with manual control, on-farm storage & sprinkler/dripd

Morocco

67

Doukkala project with sprinkler systema

Morocco

60

Open canal gravity systems with hydraulic control & irrigationd surface

Morocco

58

Doukkala project with gravity system

Mexico

55

Both Yaqui and Sinaloa projects

U. S.

53

50-85% in intensively developed areasc

Turkey

50

Traditional open canal gravity systems with manual controld

Syria

50

Basin irrigation method usedb

Kyrghyzstan

50-60

15% by sprinkler system

Mexico

48

Panuco project

Colombia

45

Coello project

Yemen

40

Large-scale gravity irrigation on the farmd

Dev.g countries

40

Averagec

 

Table 3c Overall Level

Country

(%)

Specification

Cyprus

66

Pipe conveyance systems with sprinkler and dripd

Jordan

53

Open canals with manual control, on-farm storage & sprinker/dripd

Morocco

49

Doukkala project with sprinkler systema

Morocco

42

Doukkala project with gravity systema

Morocco

42

Open canal gravity systems with hydraulic control & surface irrigationd

Kyrgbyzstan

40-45

small stream reservoirs recapture part of drainage flow in Chu Valley, plus 10% groundwater usec

U.S.

41

Averagec

Mexico

37

Sinaloa project

Philippines

36

Upper Pampanga and Aurora projectsa

Mexico

34

Yaqui project

Turkey

30

Traditional open canal gravity systems with manual controld

Syria

30

b

Dev.g countries

30

Average.

Colombia

30

Coello project

Thailand

28

Two Lam Pao areas with hip rainfall, low crop intensity in dry seasons!

Mexico

26

Panuco project

Yemen

20

Large-scale gravity spate irrigationd

 

Table 3d Sector Level

Country

(%)

Specification

Egypt

89

Nile basin estimate

U.S.

87

Based on data from 17 Western States of U.S.

Israel

80

b

Ethiopia

60-80

b

Syria

60

Average

Jordan

42

38 % for surface distribution and 70% for direct pipe distribution

 

Sources:

a), b), c) and d) are reference sources referred before (see footnote 1); f) Le Moigne, 1992b

There is kale data available on sector efficiency (Ei). In the United States, Ei has been estimated at 87 percent. Two reasons contribute to the high rate: i) the repeated use of water in different activities in a basin, or in several basins after inter-basin transfers take place, that results in improved efficiency. For example, in the seventeen Western States, 46 percent of irrigation waters are reused (Frederiksen, 1992). ii) intensive use of high irrigation technology. More than 40 percent of the irrigation lands are equipped with sprinkler systems and 3 percent with drip systems. Both systems use water more efficiently than other commonly used techniques. By contrast, the irrigation sector efficiency in Syria is 60 percent. The current flood irrigation method is the main cause of a low Ei. Water losses of 50 percent are common for such methods. Detailed analyses on Israel, Egypt and Jordan will be presented in the later sections of this paper.