Irrigation Engineering | Introduction & Types of Irrigation | Civil Engineering | #CiviLSoL

Science of artificial application of water to the land, in accordance with crop requirements is known

as irrigation.

Techniques of water distribution in the field

1. Free flooding

2. Border flooding

3. Check flooding

4. Basin flooding

5. Furrow irrigation

6. Sprinkler irrigation

7. Drip irrigation

11.1 QUALITYOFIRRIGATION WATER

Sediment When fine sand from water is deposited on sandy soils, the fertility is improved. If the

sediment has been derived from eroded areas, it may reduce the fertility.

Soluble Salts The critical self-concentration in the irrigation water depends upon many factors.

However, amount in excess of 700 ppm is harmful to some plants and more than 2000 ppm is

injurious to all crops.

Low salinity (C1

) – 100 to 250 micro mhos/cm at 25°C

Medium salinity (C2

) – 250 to 750 micro mhos/cm at 25°C

High salinity (C3

) – 750 to 2250 micro mhos/cm at 25°C

Very high salinity (C4

) – more than 2250 micro mhos/cm at 25°C

Sodium Ions to other Cations (Sodium Absorption Ratio)

Low sodium water (S1

) → SAR = 0 to 10

Medium sodium water (S2

) → SAR = 10 to 18

High sodium water (S3

) → SAR = 18 to 26

Very high sodium water (S4

) → SAR > 26

S1 – Can be used for irrigation on all soils.

S2 – Not suitable for fine textured soil.

S3 – May be used with good drainage, high leaching, gypsum addition, etc.

S4 – Not suitable.

Concentration of Toxic Elements

The wastewater containing soap, etc., should be used with great care.

Boron concentration.

Above 0.3 ppm – toxic to certain plants

Above 0.5 ppm – dangerous to nuts and deciduous fruits

– cotton is moderately tolerant

– dates, asparagus tolerant

Above 4 ppm – no plant can tolerate.

Bacterial Contamination

Harmful, only if the crop is eaten without being cooked. Contaminated wastewater can be used for

crops like cotton which are processed after harvesting.

Water Requirement of Crops

Water requirement of a crop means the total quantity and the way in which a crop requires water, from

time to time it is sown to the time it is harvested.

Some Definitions

Crop period It is the time period elapsed from the instant of sowing to the instant of harvesting.

Base period It is the time between the first watering of a crop at the time of sowing to its last

watering before harvesting.

Frequently of irrigation/rotation period It is the time interval between two consecutive watering to

a crop.

Delta Total depth of water (in mm) required by a crop to come to maturity is called its delta. It may

be expressed in hectare-metre also.

Duty of water It is the number of hectares of land irrigated for full growth of a given crop by supply

of 1 m3

/sec of water continuously during the entire base period of the crop.

Relation between Delta (D) and Duty (D)

If B is the base period in days the volume of water applied to the crop during its base period

V = 1 >× 60 × 60 × 24 × B m3

.

= 864000 B m3

.

By definition of duty, one cubic metre supplied for B days matures D hectares of land. One hectares =

100 >× 100 m2

.

\ D = = 8.64 metres.

= 8640 B/D mm.

Shows approximate values of delta and duty for various crops in India

Table 11.1 Approximate value of delta and duty for various crops