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  • 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 artificial application of water to the land, in accordance with the crop requirements throughout the crop period for full fledged 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 Irrigation 1. Irrigation may contribute to water pollution through seepage into ground water. 2.Irrigation may result in colder and damper climate. 3. Over-irrigation may lead to water-logging and reduce crop-yields. 4. Procuring and supplying irrigation water is complex and expensive 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 is supplied to lower level, then it is called flow irrigation.

  • Lift Irrigation

    If the water is lifted up by some mechanical or manual means, such as by pumps, etc. and then supplied for irrigation, 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 and water from these ditches flow across the field. No attempt is made to control the flow by means of levees, etc. It is also 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 areas confined in each strip is of the order of 10 to 20 meters in width and 100 to 400 meters in length.

  • (3) Check flooding

    Check flooding is similar to ordinary flooding except that the water is controlled by surrounding the check area with low and flat levees.

  • (4) Basin Flooding

    This method is a special type of check flooding and is adopted specially for orchard trees. One or more trees are generally placed in the basin and the surface is flooded by ditch water.

  • (5) Furrow irrigation

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

  • (6) Sprinkler irrigation In 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 water requirement 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 crops such 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 of equipment.

  • Drip Irrigation

    • In this method, water is slowly and directly applied to the root zone of the plants, thereby minimizing the losses 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 in water

    •Bicarbonate concentration as related to the concentration 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, is generally measured by a factor called Sodium-Absorption Ratio (SAR) and represents the sodium hazards of water. SAR is defined as:

    𝑆𝐴𝑅 = 𝑁𝑎+

    𝐶𝑎+ +𝑀𝑔+


    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 the following characteristics: concentration of Na, Ca and Mg are 44, 3 and 1.5 milli equivalents per liter respectively and the electrical conductivity is 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 way in which a crop requires water from the time it is sown to the time it is harvested.

    Crop period

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

    Base period

    The time between the first watering of a crop at the time of its sowing to its 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 frequency of irrigation or rotation period.

    Delta (∆)

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

    Duty of water

    The duty of water can be defined as 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 (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 be applied 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 D hectares of land or 10000D m2 of area.

    Total depth of water applied on this land = 86400𝐵

    10000𝐷 =



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

    ∆= 8.64𝐵

    𝐷 meters

    ∆= 864𝐵

    𝐷 cm

  • Water Requirements of Crops

    Factors on which duty depends

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

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

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

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

    Efficiency of cultivation method: If the cultivation method is less efficient and faulty, resulting in the wastage of water, the duty of water will naturally 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 the Rabi 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 very dry. In such a case, the soil is moistened with water, so as to help in sowing of the crops. This is known as Pale


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