1 part b3: irrigation b3.1 irrigation techniques

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Part B3: Irrigation

B3.1 Irrigation techniques

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B3.2 Irrigation techniquesTopics

• Surface irrigation– Basin irrigation, border irrigation, furrow

irrigation

• Rainwater harvesting– Bunds, microcatchments,

• “Modern” irrigation techniques– Spray irrigation, micro irrigation

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B3.2.1 Irrigation techniquesSurface irrigation: Flow

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B3.2.1 Irrigation techniques Surface irrigation: Flow

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B3.2.1 Irrigation techniquesSurface irrigation: Inlet arrangements

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B3.2.1 Irrigation techniquesSurface irrigation: Inlet arrangements

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B3.2.1 Irrigation techniquesSurface irrigation: Inlet arrangements

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Tf = Time to reach the opposite end of the field (hr)

Ta = Application time (hr)

B3.1.4 Fundamentals of irrigation Surface irrigation: The quarter time rule

4a

f

TT

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B3.2.1 Irrigation techniquesSurface irrigation: Basin irrigation

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B3.2.1 Irrigation techniques Surface irrigation: Flow

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B3.2.1 Irrigation techniquesSurface irrigation: Basin irrigation

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B3.2.1 Irrigation techniquesSurface irrigation: Basin irrigation: Scaling

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B3.1.4 Fundamentals of irrigation Surface irrigation: Basin irrigation: Scaling

Stream size (l/s) Sand Sandy loam

Clay loam Clay

15 0.01 0.03 0.06 0.10

30 0.02 0.06 0.12 0.20

60 0.04 0.12 0.24 0.40

90 0.06 0.18 0.36 0.60

120 0.08 0.24 0.48 0.80

150 0.10 0.30 0.60 1.00

180 0.12 0.36 0.72 1.20

210 0.14 0.42 0.84 1.40

240 0.16 0.48 0.96 1.60

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B3.2.1 Irrigation techniquesSurface irrigation: Basin irrigation: Problems

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B3.2.1 Irrigation techniquesSurface irrigation: Basin irrigation: Terracing

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B3.2.1 Irrigation techniquesSurface irrigation: Border irrigation

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B3.2.1 Irrigation techniquesSurface irrigation: Border irrigation

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B3.2.1 Irrigation techniquesSurface irrigation: Border irrigation

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B3.2.1 Irrigation techniquesSurface irrigation: Border irrigation: Scaling

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B3.2.1 Irrigation techniques Surface irrigation: Border irrigation: Scaling

Soil type Irrigation depth (mm)

Slope (%)

Width (m)

Length (m)

Unit stream (l/s/m)

Sand 100 0.2 12-30 60-100 10-15

0.4 10-12 60-100 8-10

0.8 5-10 75 5-7

Sand 150 0.2 15-30 90-300 4-6

0.4 10-12 90-180 3-5

0.8 5-10 90 2-4

Sand 200 0.2 15-30 350+ 3-6

0.4 10-12 180-300 2-4

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Soil type Humid areas Arid areas

Bare soil Good crop cover

Bare soil Good crop cover

Sand 0.3 1.0 1.0 2.0

Clay 0.5 2.0 2.0 5.0

B3.2.1 Irrigation techniques Surface irrigation: Border irrigation: Scaling

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B3.2.1 Irrigation techniquesSurface irrigation: Border irrigation: Problems

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B3.2.1 Irrigation techniquesSurface irrigation: Border irrigation: Problems

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B3.2.1 Irrigation techniquesSurface irrigation: Furrow irrigation

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B3.2.1 Irrigation techniquesSurface irrigation: Furrow irrigation

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B3.2.1 Irrigation techniquesSurface irrigation: Furrow irrigation

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B3.2.1 Irrigation techniquesSurface irrigation: Furrow irrigation

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B3.2.1 Irrigation techniquesSurface irrigation: Furrow irrigation

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B3.2.1 Irrigation techniquesSurface irrigation: Furrow irrigation: Infiltration

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B3.2.1 Irrigation techniquesSurface irrigation: Furrow irrigation: Scaling

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B3.2.1 Irrigation techniquesSurface irrigation: Furrow irrigation: Scaling

Slope (%)

Max stream

size (l/s)

Average irrigation depth (mm)

Clay Loam Sand

75 150 50 100 150 50 75 100

0.05 3.0 300 400 120 270 400 60 90 150

0.1 3.0 340 440 180 340 440 90 120 190

0.2 2.5 370 470 220 370 470 120 190 250

0.3 2.0 400 500 280 400 500 150 220 280

0.5 1.2 400 500 280 370 470 120 190 250

1.0 0.6 280 400 250 300 370 90 150 220

1.5 0.5 250 340 220 280 340 80 120 190

2.0 0.3 220 270 180 250 300 60 90 150

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B3.2.1 Irrigation techniquesSurface irrigation: Furrow irrigation

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B3.2.1 Irrigation techniquesSurface irrigation: Furrow irrigation: problems

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B3.2.2 Irrigation techniquesRainwater harvesting

• The collection and concentration of runoff

• Sits between rain-fed agriculture and traditional irrigation– Can produce a crop where none is possible

with simple rain catchment

• Usually in arid and semi-arid areas but also suited to semi tropical

• Rainwater is purer than ground or surface water– salinity

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B3.2.2 Irrigation techniquesRainwater harvesting:

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B3.2.2 Irrigation techniquesRainwater harvesting

Production costs

Cash crops/income

Yields

Salinity hazard

Reliability

Rain fed agriculture

Rainwater harvesting

Irrigated agriculture

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B3.2.2 Irrigation techniquesRainwater harvesting: limitations

• Climatic fluctuations– Yields cannot be guaranteed

• Potential up and downstream conflict (but less than “traditional” irrigation

• Some scientific uncertainty

• Large schemes difficult to implement

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B3.2.2 Irrigation techniquesRainwater harvesting

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C = Catchment

Ca = Cultivated area

ETcr = Crop evapotranspiration

P = Design rainfall

k = Runoff coefficient

= Efficiency

B3.2.2 Irrigation techniquesRainwater harvesting: Catchment – cultivated area ratio (C:Ca)

crET PC

Ca Pk

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B3.2.2 Irrigation techniquesRainwater harvesting: Efficiency

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B3.2.2 Irrigation techniquesRainwater harvesting: Design Rainfall: curve

0.01

0.050.10.2

0.5 1 2 5

10

30

50

70

90

95

9899

99.8

99.9

99.95

99.99

0.02

99.98

0.1

1

10

Percentage of discharge exceeding

Dis

char

ge

(m3/s

)

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B3.2.2 Irrigation techniquesRainwater harvesting: Design Rainfall: Exceedance table

Jan Feb. Mar Apr May Jun Jul Aug Sep Oct Nov Dec

10% 200 60 150 250 250 240 200 200 170 370 390 300

20% 170 40 75 220 200 200 170 160 150 340 340 240

30% 160 18 65 210 190 190 160 150 145 310 310 190

40% 155 11 60 200 140 140 140 120 140 300 300 160

50% 120 7 55 190 85 110 120 110 120 290 290 110

60% 90 5 47 170 80 105 105 96 100 270 270 105

70% 60 1 40 150 74 100 100 90 90 250 250 90

80% 18 0 18 140 65 95 90 80 55 200 200 55

90% 16 0 4 90 60 90 40 72 40 190 190 40

99% 12 0 0 60 0 60 0 60 50 18 140 18

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B3.2.2 Irrigation techniquesRainwater harvesting: Microcatchments

• Small (thus the name) 1-1000m2

• Catchment and cropping areas adjacent

• Crops are usually a single tree/catchment or small annual crop

• No overflow

• Small area ratio (1:1 – 10:1)

• Tend to be in series of units

• Efficiency 0.5-0.6

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B3.2.2 Irrigation techniquesRainwater harvesting: Microcatchments

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B3.2.2 Irrigation techniquesRainwater harvesting: Microcatchments: Negarims

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B3.2.2 Irrigation techniquesRainwater harvesting: Microcatchments: Negarims

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B3.2.2 Irrigation techniquesRainwater harvesting: Microcatchments: Negarims

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B3.2.2 Irrigation techniquesRainwater harvesting: Microcatchments: Semi circular bunds

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B3.2.2 Irrigation techniquesRainwater harvesting: Microcatchments: Semi circular bunds

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B3.2.2 Irrigation techniquesRainwater harvesting: Microcatchments: Semi circular bunds

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B3.2.2 Irrigation techniquesRainwater harvesting: Microcatchments: Semi circular bunds

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B3.2.2 Irrigation techniquesRainwater harvesting: Microcatchments: Contour bunds

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B3.2.2 Irrigation techniquesRainwater harvesting: Microcatchments: Contour bunds

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B3.2.2 Irrigation techniquesRainwater harvesting: Macrocatchments

• Big 750-10,000m2

• Used for all types of crops

• Often includes overflow structures

• larger area ratio (10:1– 100:1)

• Efficiency 0.2-0.4

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B3.2.2 Irrigation techniquesRainwater harvesting: Macrocatchments Stone bunds

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B3.2.2 Irrigation techniquesRainwater harvesting: Macrocatchments Stone bunds

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B3.2.2 Irrigation techniquesRainwater harvesting: Macrocatchments Stone bunds

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B3.2.2 Irrigation techniquesRainwater harvesting: Macrocatchments: Hillside conduits

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B3.2.2 Irrigation techniquesRainwater harvesting: Macrocatchments: Hillside conduits

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B3.2.2 Irrigation techniquesRainwater harvesting: Macrocatchments: Hillside conduits

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B3.2.2 Irrigation techniquesRainwater harvesting: Macrocatchments: Hillside conduits

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B3.2.2 Irrigation techniquesRainwater harvesting: Floodwater harvesting

• Can be diverted to conventional-style irrigation or microcatchments

• Variable size Ha – km2

• Used for all types of crops

• Variable area ratio (1:1– 10,000:1)

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B3.2.2 Irrigation techniquesRainwater harvesting: Floodwater harvesting (water spreading)

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B3.2.2 Irrigation techniquesRainwater harvesting: Floodwater harvesting (water spreading)