System Selection

The first decision that an irrigation designer must make is the selection of the irrigation method. This choice depends on both physical and socioeconomic factors, including the cost, availability, and quality of the water supply; the soil type; the field topography and geometry; the crop type and value; the labor cost and availability, material costs, energy costs; and the practicability and availability of the various technologies [140]. Table 5.14 gives a brief summary of how these factors affect selection of the irrigation system. The listed characteristics are not strict guidelines. Economics and innovative design often can supersede physical limitations.

Table 5.14. Characteristics that favor each of the irrigation methods

Surface

Sprinkler

Factor

Irrigation

Irrigation

Microirrigation

Water cost

Low

Medium

High

Water availability

Periodic or irregular

Regular

Continuous

Water cleanliness

Any

Minimal trash

Clean

or sand

Soil infiltration

Medium to

Medium to high

Any

low rate; uniform

Soil water storage

High

Medium

Low

Surface topography

Uniform, low slope

Uniform to somewhat

Irregular

irregular

Crop geometry

Any

Low-growing

Wide-spaced

Water stress sensitivity

Low

Moderate

High

Crop value

Low

Moderate

High

Cost of labor

Low

Varies with

High

the system

Cost of energy

High

Low

Moderate

Capital availability

Low

Medium to high

High

Technology availability

Low

Medium to high

High

Table 5.15. Estimated seasonal water application efficiency by method of irrigation

Efficiency

Surface

Sprinkler

Micro

Potential (%)

60-80

75-90

90-95

Actual (%)

30-80

50-80

65-90

The water application efficiency of the various irrigation methods varies with conditions and system type, and it is difficult to estimate (Table 5.15). Surface irrigation is often relatively inefficient because of lack of water control and the dependence on inherently variable soils. The potential efficiency of microirrigation is very high but requires good system design, maintenance, and operation. Sprinkler irrigation also can be efficient, especially when used under low-wind conditions. Measurements in the United States show that these systems often do not reach their potentials [105].

To support system selection, Table 5.16, containing indicative values for initial investment costs, economic equipment life, and maintenance costs, is provided (complementary information is given by Keller [141]). The table also includes the expected range for the seasonal application efficiencies of the systems. This information is helpful for estimating the gross irrigation water requirements [Section 5.1, Eq. (5.92)]. However, Table 5.16 does not refer to traditional surface irrigation, which has very low investment in equipment and often produces uniformity and efficiency near the lower values in Table 5.15.

Table 5.16. Costs and efficiencies of different types of modern on-farm irrigation systems

Irrigation Method

Equipment Initial Cost

Economic

Annual Maintenance

Application

and Type

(U.S. dollars/ha)a

Life (years)

(% of cost)

Efficiency (%)

Surface precision

Basin (level)

370-1,085

10-15

10

70-90

Border

370-1,085

10-15

10

70-85

Furrow

150-750

10-15

3-5

65-85

Conveyance

Lined

400-1,250

15

3

Piped

800-2,500

20

1

Automation

300

10

5

Sprinkle

Lateral

Hand-move

450-675

15

2

65-80

End-tow

600-950

10

3

65-75

Side-roll

800-1,100

15

2

65-80

Side-move

950-1,350

15

4

65-80

Hose-fed

450-675

5-20

3

60-80

Traveling gun

950-1,200

10

6

55-70

Center-pivotb

Standard (400 m)

1,100

15

5

70-85

w/Corner

1,200

15

6

65-85

Long (500 m)

700

15

5

65-85

Linear Moveb

Ditch-feed

1,100-1,300

15

6

65-85

Pipe-feed

1,600-2,050

15

6

65-85

Solid-Set

Portable

2,700-3,250

15

2

65-75

Permanent

2,300-3,500

20

1

65-75

Microirrigation

Orchard

Drip/spray

1,500-3,500

10-20

3

75-90

Bubbler

2,500-4,000

15

2

60-85

Row-crop

Drip Tubing

2,000-5,000

10-20

3

65-90

Thin-wall tubing

1,650-3,000

1-20

20

b Costs more than double when systems irrigate smaller areas (<30 ha). Source: Adapted from [141].

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