[GATE NOTES] Irrigation – GATE, IES, Govt Exams – Handwritten Notes – Free Download PDF

1. Water Requirements of crops
2. Methods of Irrigation
3. Gravity Dams
4. Spill Ways
5. Diversion of Head Works
6. Design of Unlined Alluvial Canals by silt Theories
7. Water Logging and Drainage
8. Quality of Irrigation Water and Sodic soils

Irrigation :Science which deals with aritificial supply of water to the crops is known as Irrigation.

A regulation controls the flow of water into the canal.

Irrigation system comprises of hydraulic structures like dams, weirs, barrage, canal system, cross drainage works, regulators , canal falls and canal escapes (surplus escape and silt escape)

Hydroscopic water : Thin layer of water surrounding the soil grains which the roots of plants cannot absorb.

Types of water :

Gravitational water
Capillary water
Hydroscopic water

The moisture content is expressed as percentage at ultimate wetting point us called hygroscopic coefficient.

Hygroscopic water : It consists of two parts :
1. Amount of moisture absorbed from atmosphere by the soil grains
2. Thin film of moisture sticking to the soil grains which cannot be extracted by the plant.

Capillary water :

The amount of moisture stored in capillary pores which can be extracted by the plant is called capillary water or available water.
Saturation capacity : A state where all the voids are filled with moisture.
Field capacity : Amount of moisture retained in the soil against pull of gravity.
Water stored in capillary pore against gravity pull in the root zone is field capacity.
Temporary witting point : Plants can make use of water available in the soil.
Permanent Witting point : Plants recovers only with application of water.
Ultimate Witting point : Even with application if water, plant cannot receive i.e plant is dead.

Surface Irrigation Methods :

1. Flooding method :
a. Uncontrolled flooding ex inundation irrigation
b. Controlled flooding
-field channel method
-border irrigation method
-check or leave method
-basin method

2. Furrow method
3. Contour farming

Sub surface Irrigation method :

1. Natural sub surface
2. Aritificial subsurface
3. Drip Irrigation method

Infiltration opportunity time (IOT) is the difference of Advance time and recession time.
Using IOT, deep percolation loss is calculated from infiltration profiles. Knowing the deep percolation loss and tail water run off loss, application efficiency is calculated

Advance time – Time at which the water reaches a particular section.
Recession time – Time at which the water seize from that section.

Furrow method :
Furrow are small channels with mild slope which carry water with low velocities. Due to lateral seepage of water, the crops are grown.The water is directly supplied to the root zone.