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Irrigation Water Requirements

Canal Irrigation System

Design of Canals

Diversion Headwork

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Regulating Structures

Cross-Drainage Structures

Water-Logging and Drainage

Introduction Irrigation and its Method

Definition of Irrigation
Irrigation is defined as the science of artificial application of water to the land for the purpose of the raising crops. Optimum crop yield is the main objective of irrigation.

Necessity of Irrigation

  • Uneven Distribution of the Rainfall
    It is necessary when the rainfall in the region is adequate but it is not evenly distributed over the time.
  • Growing Perennial Crops
    As rainfall is not regular, irrigation is necessary to yield the production of perennial crops.
  • Inadequate Rainfall
    When rainfall at the place is in adequate to meet the water requirement of the crops the irrigation is necessary, this is generally for the arid and semi-arid region.
  • Increasing the Yields of Crops
    If the supply of water is properly controlled, the yield of the crops per hectare is substantially increased by irrigation.
  • Growing Superior Crops
    Irrigation contributes a lot in growing the superior crops that require the high rate of supply of water.
  • For Controlled Water Supply
    Water supply has always been an issue where the water availability is sparse. So irrigation helps in controlled supply of water.
  • Development of Agriculture in Desert Areas
    Irrigation does help in the development of production and productivity / agriculture in desert areas too. Unused land can be irrigated and can be made cultivable

Advantages of Irrigation

  • Yield of Crops.
  • Protection from famine.
  • Improvement in cash crops.
  • Prosperity of farmers.
  • Source of revenue.
  • Hydroelectric Power generation.
  • Water Supply.

Disadvantages of Irrigation

  • Rising of water table.
  • Breeding of bacteria and mosquitoes causing the outbreak of diseases like malaria.
  • Water pollution by seepage.
  • Cold and damp climate.
  • Loss of valuable lands.

Status and Need of Irrigation in Nepal 
Total area = 1,47,181 km2
Total cultivated area = 2.6 million ha
Total irrigable land = 66%of cultivable land = 1.7 million ha
Total irrigation facilities = 60% if irrigable land =1.06 million ha
90% of people are directly or indirectly depend on agriculture. Irrigation facilities are developed only in Terai but small and negligible in the hilly region.

Project Categories of Irrigation

  1. Extensive irrigation scheme
  2. Intensive irrigation schemes
  3. Commanded area development schemes

Large Irrigation Project in Nepal

  1. Sunsari Morang Irrigation Project
  2. Mahakali Irrigation Project
  3. Gandaki Irrigation Project
  4. Koshi Irrigation Project

Medium Irrigation Project

  1. Babai
  2. Sikta
  3. Marchawa
  4. kamala
  5. Bagmati
  6. Kankai

Nepal government have launched the FMIS (farmer management irrigation systems) scheme to develop the irrigation purpose in the hilly terrain of Nepal where the management and use of the irrigation project are the sole responsibility of farmers. This helps in encouraging the feeling of ownership among them.

Types of Crops as per Time of Production

  • Rabi Crops
    These crops are usually cultivated during 1st October to 31st March. They are termed as winter crops. Rabi crops are wheat, barley, gram, mustard, potatoes, etc
  • Kharif Crops
    These crops are usually cultivated during 1st April to 30th September. They are termed as summer crops. Kharif crops are rice, maize, cotton, tobacco, etc.
    Water required by the Kharif crops is about 2-3 times the amount needed by Rabi crops.

Commanded Area 

  • Gross Commanded Area (GCA)
    It is the total area which can be economically irrigated from irrigation system without considering the limitation on the quantity of available water. It includes both cultivable and uncultivable area. It includes residential areas, roads, ponds, lands etc.
  • Culturable or Cultivable Commanded Area (CCA)
    It is the cultivable part of the GCA and includes all the lands of GCA on which cultivation is possible,  include pastures and fallow lands which can be made cultivable.

Intensity of Irrigation
It is the percentage of CCA proposed to be irrigated to be irrigated in a given season.

Method of Field Irrigation and Their Suitability

  1. Surface Irrigation
    Here, the water is directly applied to the surface of the land, it is further categorized as:
    1. Flow Irrigation
      When water flows from the higher level and it is supplied to lower level by the mere action of gravity, it is flow irrigation. It is further sub divided as:
      1. Perennial Irrigation
        Here, constant and continuous water supply is assured to the crop in accordance with the requirement of crops throughout the crop period.
      2. Flood Irrigation
        Here, soil is kept submerged and thoroughly flooded with water so as to cause thorough saturation of land. It is also called inundation irrigation.
    2. Lift Irrigation
      Here, water is lifted up by some mechanical or manual means such as by pumps, etc and then supplied for irrigation. Eg- Narayani irrigation project, Chitwan.
  2. Sub-surface Irrigation
    1. Natural Subsurface
      When underground irrigation is achieved simply by natural processes without any additional extra efforts then it is called natural subsurface.
    2. Artificial Subsurface
      When a system of open-jointed drain is artificially laid below the soil so as to supply water to crops by capillarity then it is called artificial subsurface irrigation,
      There are various ways in which the irrigation water can be applied to the fields:
      1. Free Flooding
        In this methodwater is supplied through ditches. It flows across the field. This method is mostly used in India, U.S.A., Egypt, etc.
        Free Flooding
         Free Flooding
      2. Border Flooding
        In this farm is divided into no. of strips. The width & length of each strip should not exceed 9-18 m & 100 – 400 m respectively.
        Border Flooding
        Border Flooding
      3. Check Flooding
        In this case, the farm is divided into small check areas. These are surrounded on all sides by low, flat ridges.
        Check Flooding
        Check Flooding
      4. Basin Flooding
        It is same as check except that it is applied to an orchard.
        Basin Flooding
      5. Furrow Irrigation
        In this case, crops are grown by supplying water between crops rows. This method consists in applying water to the field by furrow supplying 8 – 24 cm per 100 m.
        Furrow Flooding
        Furrow Flooding
      6. Sprinkler Irrigation
        This is an irrigation system based on overhead sprinklers, sprays or guns, installed on permanent risers. You can also have the system buried underground and the sprinklers rise up when water pressure rises, which is a popular irrigation system for use on golf courses and parks.
        Sprinkler Method
        Sprinkler Method
      7. Drip Irrigation
        This is known as the most water-efficient method of irrigation. Water drops right near the root zone of a plant in a dripping motion. If the system is installed properly you can steadily reduce the loss of water through evaporation and runoff.
        Drip Method
        Drip Method

Planning of Irrigation Project

  • The main objective is to meet the demand and water availability as closely as possible.
  • Water availability estimation.
  • Crop planting technique.
  • Estimating irrigation demand for the planned crops.
  • Matching supply and demand.

Stages of Planning

  • Primary Planning
  • Feasibility Study
  • Final Design

Factors to be Considered While Planning

  • Type of project and general plan of irrigation.
  • Location, extend and types of irrigation land.
  • Crop water requirement.
  • Culturable area.
  • Cost of work.
  • Needs of immediate and future drainage.
  • Evaluation of benefits.
  • Method of financing.
  • Types and location of engineering work.
  • The annual cost of water to the farmer.

Irrigation Engineering and Hydraulic structures book by SK GARG 
Hydraulic Structures by P. Novak, A.I.B. Moffat and C. Nalluri, R. Narayanan
NPTEL irrigation materials
Irrigation Enginnering by N.N Basak
Irrigation, Water Power and Water Resources Engineering by K.R Arora






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