Chapter: Irrigation Techniques and Quality of Irrigation Water · 2018-12-27 · (6) Sprinkler...

Hydrology, Irrigation and Flood Management (CE 4163)

Chapter: Irrigation Techniques and Quality of Irrigation Water

Reference Book: Irrigation Engineering and Hydraulic Structures by S.K. Garg

Lecture prepared by

Md Nuruzzaman

Lecturer, Department of Civil Engineering

Bangladesh Army University of Engineering and Technology (BAUET)

Definition

Irrigation may be defined as the science of artificialapplication of water to the land, in accordance with thecrop requirements throughout the crop period for fullfledged nourishment of the crops.

Advantages of Irrigation

1. Increase in food production

2. Optimum benefits

3. Elimination of mixed cropping

4. General prosperity

Advantages of Irrigation

5. Generation of Hydro-electric power

6. Domestic water supply

7. Facilities of communication

8. Inland navigation

9. Afforestation

Disadvantages of Irrigation1. Irrigation may contribute to water pollution throughseepage into ground water.2.Irrigation may result in colder and damper climate.3. Over-irrigation may lead to water-logging and reducecrop-yields.4. Procuring and supplying irrigation water is complex andexpensive in itself.

Types of Irrigation

1. Surface Irrigation

(a) Flow irrigation

(b) Lift Irrigation

2. Sub-surface irrigation

Flow Irrigation

When the water is available at a higher level, and it issupplied to lower level, then it is called flow irrigation.

Lift Irrigation

If the water is lifted up by some mechanical or manualmeans, such as by pumps, etc. and then supplied forirrigation, then it is called lift irrigation.

Types of flow irrigation

(a) Perrennial irrigation

(b) Flood irrigation

Sub-surface irrigation

When the underground water nourishes the plant roots by capillarity, it is termed as sub-surface irrigation.

Techniques of Water Distribution in the farms

(1) Free Flooding or Ordinary flooding

In this method, ditches are excavated in the field andwater from these ditches flow across the field. No attemptis made to control the flow by means of levees, etc. It isalso called wild flooding.

(2) Border Flooding

In this method, the land is divided into a number of strips,separated by low levees called borders. The land areasconfined in each strip is of the order of 10 to 20 meters inwidth and 100 to 400 meters in length.

(3) Check flooding

Check flooding is similar to ordinary flooding except thatthe water is controlled by surrounding the check area withlow and flat levees.

(4) Basin Flooding

This method is a special type of check flooding and isadopted specially for orchard trees. One or more trees aregenerally placed in the basin and the surface is flooded byditch water.

(5) Furrow irrigation

In furrow irrigation method, only one-fifth to one-half ofthe land is wetted by water. Furrows are narrow ditchesexcavated between rows of plants and carry irrigationwater through them. Furrows may be 8 to 30 cm deep andas much as 400 meters long.

(6) Sprinkler irrigationIn this method, water is applied to the soil in the form of a spray through a network of pipes and pumps. It is a kind of an artificial rain.

•Favorable conditions for Sprinkler irrigation method•When the land topography is irregular•When the land gradient is steeper.•When the land soil is excessively permeable.•When the watertable is high.

•When the area is such that the seasonal waterrequirement is low.•When the water is available with difficulty and is scarce.

Advantages of Sprinkler irrigation method

•Seepage loss is completely eliminated.

• Land levelling is not required.

•No cultivation area is lost for making ditches.

• It avoids surface runoff and its bad effects.

•Fertilizers can be uniformly applied.

•This method leaches down salts and prevents water-logging.

•Upto 80% efficiency can be achieved.

Limitations of Sprinkler irrigation method

•High winds may distort sprinkler pattern.

• In areas of high temperature and wind velocity,considerable evaporation loss may occur.

•They are not suited for larger depths of irrigation cropssuch as paddy.

• Initial cost of the system is high.

•Only sand and silt free water can be used.

• It requires larger electrical power.

•A constant water supply is needed for commercial use ofequipment.

Drip Irrigation

• In this method, water is slowly and directly applied tothe root zone of the plants, thereby minimizing thelosses by evaporation and percolation.

Quality of Irrigation water

• Impurities of Irrigation water

•Sediment concentration in water

•Total concentration of soluble salts in water

•Proportion of sodium ion to other ions

•Concentration of p5otentially toxic elements present inwater

•Bicarbonate concentration as related to theconcentration of calcium plus magnesium

•Bacterial contamination

Classification of irrigation water based on salinity

Sodium Absorption Ratio (SAR)

The proportion of sodium ions present in the soils, isgenerally measured by a factor called Sodium-AbsorptionRatio (SAR) and represents the sodium hazards of water.SAR is defined as:

𝑆𝐴𝑅 =𝑁𝑎+

𝐶𝑎+ +𝑀𝑔+

2

Where, the concentration of the ions is expresses in equivalent per million (epm)

Classification of irrigation water based on SAR

Problem 1.1: What is the classification of irrigation water having thefollowing characteristics: concentration of Na, Ca and Mg are 44, 3 and1.5 milli equivalents per liter respectively and the electrical conductivityis 500 micro-mhos/cm at 250C?

Hydrology, Irrigation and Flood Management (CE 4163)

Chapter: Water Requirements of Crops

Reference Book: Irrigation Engineering and Hydraulic Structures by S.K. Garg

Lecture prepared by

Md Nuruzzaman

Lecturer, Department of Civil Engineering

Bangladesh Army University of Engineering and Technology (BAUET)

Water Requirements of Crops

Water Requirements of Crop

The term ‘water requirement of crop’ means the total quantity and the wayin which a crop requires water from the time it is sown to the time it isharvested.

Crop period

The time period that elapses from the instant of its sowing to the instant ofits harvesting is called crop-period.

Base period

The time between the first watering of a crop at the time of its sowing toits last watering before harvesting is called Base period.

Water Requirements of Crops

Frequency of irrigation or Rotation period

The time interval between two consecutive waterings is called frequencyof irrigation or rotation period.

Delta (∆)

The total depth of water (in cm) required by a crop to come to maturity iscalled its delta.

Duty of water

The duty of water can be defined as the number of hectares of landirrigated for full growth of a given crop by supply of 1 m3/sec of watercontinuously during the entire base period (B) of that crop.

Water Requirements of Crops

Relation between duty and delta

Let there be a crop of base period B days. Let one cumec of water beapplied to this crop on the field for B days.

Now the volume of water to be applied to this crop during B days

= V = 1 x 60 x 60 x 24 x B m3 = 86400B m3

By definition of duty (D), one cumec supplied for B days matures Dhectares of land or 10000D m2 of area.

Total depth of water applied on this land =86400𝐵

10000𝐷=

8.64𝐵

𝐷

By definition, this total depth of water is called delta (∆)

∆=8.64𝐵

𝐷meters

∆=864𝐵

𝐷cm

Water Requirements of Crops

Factors on which duty depends

Type of Crop: For a crop requiring more water, duty is less and viceversa.

Climate and Season: Duty will be less in hot season as evaporation losswill be higher and vice versa.

Useful rainfall: More the useful rainfall, less will be the requirement ofirrigation water, and hence, more will be the duty of irrigation water.

Type of Soil: If the permeability of the soil under the irrigated crop ishigh, the loss due to percolation will be more and hence, the duty will beless.

Efficiency of cultivation method: If the cultivation method is lessefficient and faulty, resulting in the wastage of water, the duty of water willnaturally be less.

Water Requirements of Crops

Kharif-Rabi ratio or Crop ratio

The ratio of proposed areas, to be irrigated in Kharif season to that in theRabi season is called Kharif-Rabi ratio. This ratio is generally 1:2.

Paleo irrigation

Sometimes, in the initial stage before the crop is sown, the land is verydry. In such a case, the soil is moistened with water, so as to help insowing of the crops. This is known as Paleo irrigation.

Kor watering

The first watering which is given to a crop, when the crop is a fewcentimeters high, is called kor-watering. It is usually the maximum singlewatering followed by other waterings at usual intervals, as required bydrying of leaves.

Water Requirements of Crops

Kor-period

The kor-watering must be applied within a fixed limited period, called Kor-period.

Cash Crops

A cash crop may be defined as a crop, which has to be encashed in themarket for processing as it cannot be consumed directly by thecultivators.

Optimum Water Depth

The quantity of water at which the yield is maximum, is called theoptimum water depth.

Water Requirements of Crops

Irrigation Efficiencies

Efficiency of water conveyance

It is the ratio of the water delivered into the fields from the outlet point ofthe channel, to the water entering into the channel at its starting point.

Efficiency of water application

It is the ratio of the quantity of water stored into the root zone of thecrops to the quantity of water actually delivered into the field. It is alsocalled farm efficiency.

Water Requirements of Crops

Irrigation Efficiencies

Efficiency of water storage

It is the ratio of the water stored in the root zone during irrigation to thewater needed in the root zone prior to irrigation.

Efficiency of water use

It is the ratio of the water beneficially used, including leaching water, tothe quantity of water delivered.

Water Requirements of Crops

Water Requirements of Crops

Water Requirements of Crops

Water Requirements of Crops

Water Requirements of Crops

Water Requirements of Crops

Water Requirements of Crops

Water Requirements of Crops

Water Requirements of Crops

Water Requirements of Crops

Water Requirements of Crops

Water Requirements of Crops

Water Requirements of Crops

Water Requirements of Crops

Water Requirements of Crops

Water Requirements of Crops

Example 2.15 After how many days will you supply water to soil

in order to ensure sufficient irrigation of the given crop, if (i) Field

capacity of the soil = 28% (ii) Permanent wilting point = 13%

(iii) Effective depth of root zone = 70 cm (iv) Dry density of soil

= 1.3 gm/cm3 (v) Daily consumptive use by crop = 12 mm.

Water Requirements of Crops

Canal Irrigation System

Canal Irrigation System

Intensity of Irrigation

Canal Irrigation System

Canal Irrigation System

Canal Irrigation System

Canal Irrigation System

Canal Irrigation System

Canal Irrigation System

Canal Irrigation System

Hydrology, Irrigation and Flood Management (CE 4163)

Chapter: Water logging, salinity and reclamation

Reference Book: Irrigation Engineering and Hydraulic Structures by S.K. Garg

Lecture prepared by

Md Nuruzzaman

Lecturer, Department of Civil Engineering

Bangladesh Army University of Engineering and Technology (BAUET)

Water logging, salinity and reclamation

Water logging, salinity and reclamation

Problems due to water logging

Water logging, salinity and reclamation

Water logging, salinity and reclamation

Water logging, salinity and reclamation

The water logging can be controlled only if the quantity of water into the

soil below is checked and reduced. Various measures adopted for

controlling water-logging are enumerated below:

❖Lining of canals and Water courses

❖Reducing the intensity of irrigation

❖By introducing crop rotation

❖By optimum use of water

Controls of Water logging

Water logging, salinity and reclamation

❖ By provision of an Efficient Drainage system

❖ By Improving the Natural Drainage of the Area

❖ By adopting consumptive use of surface and subsurface water

Controls of Water logging

Water logging, salinity and reclamation

Reclamation of Saline and Alkaline Lands

Land reclamation is a process by which an uncultivable land is made fit

for cultivation. Saline and water logged lands give very less crop yields

and therefore almost unfit for cultivation, unless they are reclaimed.

Water logging, salinity and reclamation

Reclamation of Saline and Alkaline Lands

Every agriculture soil contains certain mineral salts in it. Some of the

salts are beneficial for plants and some of the salts are injurious to plant

growth. The injurious salts are called Alkali salts and their common

examples are Na2CO3, Na2SO4, and NaCl.

** Na2CO3 named Black Alkali is the most harmful

** NaCl is the least harmful

Water logging, salinity and reclamation

Efflorescence and Saline soil

This phenomenon of salts coming up in solution and forming a thin (5 to

7.5 cm) crust on the surface, after the evaporation of water, is called

efflorescence.

Land affected by efflorescence is called saline soil.

Water logging, salinity and reclamation

Alkaline soil

Saline soil is unproductive. If the salt efflorescence continues for a

longer periods , a base exchange reaction sets up, particularly if the

soil is clayey. Thus sodiumising the clay, making it impermeable, ill

aerated and highly unproductive.

Such soils are called Alkaline soil.

Water logging, salinity and reclamation

Reclamation of Salt affected Land

Efflorescence can be avoided if the water table is maintained sufficiently

(about 3m) below the roots, so that the capillary water is not able to

reach the root zone of the plant.

All those measures that prevent water-logging hold good for preventing

salinity of soil also.

Water logging, salinity and reclamation

Leaching

Land is flooded with adequate depth of water > alkali salt get

dissolved > percolated down to water table.

This process is repeated till the salts in the top layer of the land are

reduced to such as extent that some salt resistant crop can be grown.

This process is known is Leaching.

Water logging, salinity and reclamation