IRRIGATION
what is irrigation - This artificial application of water to land for supplementing the naturally available moisture in the root-zone soil for the purpose of agricultural production is termed irrigation.
Water is to be supplied to agricultural field. Hence suitable water resources are to be identified and water retaining structures are to be built. Identifying, planning and building water retaining structures like tanks and dams and carrying stored water to fields is known as water resources and irrigation engineering. Constructing canals, distributories aquaducts and regulators form part of irrigation engineering.
Three basic requirements of agricultural production are soil, seed, and water. In addition, fertilisers, insecticides, sunshine, suitable atmospheric temperature, and human labour are also needed. Of all these, water appears to be the most important requirement of agricultural production. The application of water to soil is essential for plant growth and it serves the following functions
(i) It supplies moisture to the soil essential for the germination of seeds, and chemical and bacterial processes during plant growth.
(ii) It cools the soil and the surroundings thus making the environment more favourable for plant growth.
(iii) It washes out or dilutes salts in the soil.
(iv) It softens clods and thus helps in tillage operations.
(v) It enables application of fertilisers.
(vi) It reduces the adverse effects of frost on crops.
(vii) It ensures crop success against short-duration droughts.
In several parts of the world, the moisture available in the root-zone soil, either from rain or from underground waters, may not be sufficient for the requirements of the plant life. This deficiency may be either for the entire crop season or for only part of the crop season. For optimum plant growth, therefore, it becomes necessary to make up the deficiency by adding water to the root-zone soil. This artificial application of water to land for supplementing the naturally available moisture in the root-zone soil for the purpose of agricultural production is termed irrigation.
Storage of some major dams
Dam Height (m) Storage (million cubic metres)
Bhakra (India) 226 11,320
Kishau (India,projected) 244 1,980
Tehri (India, projected) 260 3,550
Hoover (U.S.A.) 222 38,600
High Aswan (Egypt) 97 156,000
WATER RESOURCES OF INDIA
India, with a geographical area of 329 Mha (million hectares), is blessed with large river basins which have been divided into 12 major and 48 medium river basins comprising 252.8 Mha and 24.9 Mha of total catchment area, respectively. It possesses about 4 percent of the total average annual runoff of the rivers of the world. The per capita water availability of natural runoff is, however, only 2200 cubic metre per year which is about one-third of the per capita water availability in USA and Japan . The per capita water availability in India would further decrease with ever-increasing population of the country.
The annual precipitation in the country is estimated at about 4000 cubic km. This amount includes snow precipitation as well. As per the assessment of Central Water Commission (CWC), the average annual runoff of various river basins in the country is about 2333 cubic km treating both surface and ground waters as one system. More than eighty (for Himalayan rivers) to ninety (for peninsular rivers) percent of the annual runoff occurs during monsoon months. Because of this fact and other constraints, it is assessed that the total average annual potential of water available in India is about 1880 cubic km out of which only about 1140 cubic km of water can be put to beneficial use by conventional methods of development of water resources.
The basinwise average annual potential, estimated utilisable surface water, and actual utilised surface water (1989). Utilisable ground water is estimated at about 450 cubic km out of which about 385 cubic km is utilisable for irrigation alone. The primary uses of water include irrigation, hydro-electric power generation, inland water transport, and domestic and industrial uses including inland fish production. indicates the amount of utilization of water in 1985 and the projected demands of water for various purposes in the year 2025.
NEED OF IRRIGATION IN INDIA
The rainfall in India is very erratic in its spatial as well as temporal variations. The average annual rainfall for India has been estimated at 1,143 mm which varies from 11,489 mm around Cherrapunji in Assam (with the maximum one-day rainfall equal to 1040 mm) to 217 mm around Jaisalmer in Rajasthan. Besides, 75% to 90% of the annual rainfall occurs during 25 to 60 rainy days of the four monsoon months from June to September. In addition, there is also a large variation from year to year, the coefficient of variation being more than 20% for most parts of the country
Erratic behaviour of the south-west monsoon is the main cause of India’s frequent droughts and floods. The recent proposal of the Government of India on interlinking of some major rivers of the country is aimed at (i) increasing the utilizable component of the country’s water resources, and (ii) solving the problems of shortages and excesses of water in some parts of the country for different regions (8). Dependability of rainfall is thus rather low from the agriculture point of view and storage is essential to sustain crops during non-monsoon periods and also to provide water for irrigation during years of low rainfall. For a large part of any crop season, the evapotranspiration (i.e., the water need of a crop) exceeds the available precipitation and irrigation is necessary to increase food and fibre production. About 45 percent of agricultural production in India is still dependent on natural precipitation. The need and importance of irrigation in India can be appreciated from the mere fact that the country would need to produce 277 million tonnes (against the production of about 185 million tonnes for 1994-95) of food to meet the per capita requirement of 225 kg (i.e., about one-fourth of a tonne) per year for an estimated population of 1,231 million in the year 2030
DEVELOPMENT OF IRRIGATION IN INDIA
Among Asian countries, India has the largest arable land which is close to 40 percent of Asia’s arable land . Only USA has more arable land than India. Irrigation has been practised throughout the world since the early days of civilization. In India too, water conservation for irrigation has received much attention since the beginning of civilization. The Grand Anicut across the river Cauvery was built in the second century. At the beginning of the 19th century, there were a large number of water tanks in peninsular India and several inundation canals in northern India. The Upper Ganga canal, the Upper Bari Doab canal and the Krishna and Godavari delta systems were constructed between 1836 and 1866. The famines of 1876–78, 1897–98 and 1899–1900 led to the setting up of the first Irrigation Commission in 1901 to ascertain the usefulness of irrigation as a means of protection against famine and to assess the extent of irrigation development required and the scope for further irrigation work. At this time (1901) the total gross irrigated area was only 13.3 Mha which increased to 22.6 Mha in 1950 as a result of a spurt in protective irrigation schemes.
The Bengal famine of 1943 underlined the urgency of increasing agricultural production to meet the needs of the growing population. After independence, the country began an era of planned development starting with the first five-year plan in 1951. The Planning Commission assigned a very high priority to irrigation development for increasing agricultural production. Giant projects like the Bhakra-Nangal, Hirakud, Damodar Valley, Nagarjunasagar, Rajasthan canal, etc. were taken up. This resulted in a great spurt in irrigation development activities and the irrigated area increased from 22.6 Mha in 1950–51 to 68 Mha in 1986–87. In June 1993, the irrigated area was 83.48 Mha i.e., 2.39 Mha more than that in June 1992. The yearwise development of irrigation potential in India since 1950–51 and up to 1994–95. The present food grain production is slightly more than 200 million tonnes.The total ultimate irrigation potential is estimated at 115.54 Mha of which 58.47 Mha would be from major and medium irrigation schemes and the remaining from minor irrigation schemes
IRRIGATION SCHEMES MAJOR AND MEDIUM OF INDIA
Major irrigation schemes are those which have culturable command area (C.C.A.)* more than 10,000 ha. Irrigation schemes having C.C.A. between 2,000 and 10,000 ha are classed as medium irrigation schemes . The important schemes of the first two plan periods include Bhakra- Nangal, Rajasthan canal, Gandhi Sagar dam, Gandak, Kosi, Nagarjunasagar, Hirakud, Tungabhadra, Malaprabha, and Ghatprabha projects. Later, the multipurpose Beas project, Ramganga dam and canals, Sri Ramsagar, Jayakwadi, Ukai, Kadana, Sardar Sarovar, Tawa, Teesta, etc. were taken up for utilising the monsoon waters.
The performance of major and medium irrigation schemes was examined by the National Irrigation Commission (1972), the National Commission on Agriculture (1976), and several other committees. It was found that the available irrigation potential was not fully utilised. The difference between the available and utilised irrigation potential exceeds 4.0 Mha. Water logging and salinity damaged large areas. Moreover, the return in terms of increased agricultural production was far below the expectations. For all these deficiencies, the following causes were identified
(i) Need for modernisation of the pre-Plan and early-Plan systems to provide water at the outlet delivery points to farmers at the right time and in the right quantity.
(ii) Lack of adequate drainage resulting in water logging conditions due to excess water used in irrigating crops as well as due to soil characteristics.
(iii) The absence of a distribution system within the outlet and the non-introduction of rotational distribution of water to the farmers.
(iv) Inadequate attention to land consolidation, levelling and all other aspects which can promote a better on-farm management of water.
(v) Lack of anticipatory research on optimum water use, particularly in black soils with considerable moisture retention capacity.
(vi) Lack of suitable infrastructure and extension services.
(vii) Poor coordination between the concerned Government organisations in the command areas.
* Gross command area of an irrigation system is the total area which can be economically irrigated from the system without considering the limitations of the quantity of available water. Area of the cultivable land in the gross command of an irrigation system is called the culturable command area (C.C.A.).
MINOR IRRIGATION
Minor irrigation schemes include all ground water and surface water irrigation (flow as well as lift) projects having culturable command area up to 2000 ha. Minor surface water flow irrigation projects include storage and diversion works and are the only means of irrigation in several drought-prone tracts such as undulating areas south of the Vindhyas and also hilly regions. Such projects offer considerable opportunity for rural employment and also help in recharging the meagre resources of ground water in the hard rock areas. When available surface water cannot be used for irrigation through construction of flow irrigation schemes due to topographical limitations, surface water lift irrigation schemes provide the solution.
Ground water is widely distributed and provides an instant and assured source of irrigation to farmers. It improves the status of irrigation supply and helps in controlling waterlogging and salinisation in the command area of a canal. Ground water development is the major activity of the minor irrigation programme. It is mainly a cultivator’s own programme implemented primarily through individual and cooperative efforts. Finance for such programmes are arranged through institutional sources. The first large-scale venture in scientific planning and development of ground water was initiated in India in 1934 when a project for the construction of about 1,500 tubewells in the Indo-Gangetic plains in the Meerut region of Uttar Pradesh was undertaken. Adequate energy for pumping ground water is essential for near-normal production of crops when there is severe drought. Hence, energy management is also essential. Besides electricity and diesel, biogas-operated pumps need to be popularised. The use of solar energy through photovoltaic systems will, probably, be the ultimate solution to the energy problem. Wind energy should also be tapped in desert, coastal and hilly regions.
IRRIGATION PROJECTS PLANNING
Agricultural establishments capable of applying controlled amounts of water to lands to produce crops are termed irrigation projects. These projects mainly consist of engineering (or hydraulic) structures which collect, convey, and deliver water to areas on which crops are grown. Irrigation projects may range from a small farm unit to those serving extensive areas of millions of hectares. A small irrigation project may consist of a low diversion weir or an inexpensive pumping plant along with small ditches (channels) and some minor control structures. A large irrigation project includes a large storage reservoir, a huge dam, hundreds of kilometres of canals, branches and distributaries, control structures, and other works. Assuming all other factors (such as enlightened and experienced farmers, availability of good seeds, etc.) reasonably favourable, the following can be listed as conditions essential for the success of any irrigation project.
(i) Suitability of land (with respect to its soil, topography and drainage features) for continued agricultural production,
(ii) Favourable climatic conditions for proper growth and yield of the crops,
(iii) Adequate and economic supply of suitable quality of water, and
(iv) Good site conditions for the safe construction and uninterrupted operations of the engineering works.
During the last four decades, many large irrigation projects have been built as multipurpose projects. Such projects serve more than one purpose of irrigation or power generation. In India, such large projects (single-purpose or multipurpose) are constructed and administered by governmental agencies only. Most of the irrigation projects divert stream flow into a canal system which carries water to the cropland by gravity and, hence, are called gravity projects. In pumping projects, water is obtained by pumping but delivered through a gravity system.
IRRIGATION DEVELOPMENT PROJECT
A small irrigation project can be developed in a relatively short time. Farmers having land suitable for agriculture and a source of adequate water supply can plan their own irrigation system, secure necessary finance from banks or other agencies, and get the engineering works constructed without any delay. On the other hand, development of a large irrigation project is more complicated and time-consuming. Complexity and the time required for completion of a large project increase with the size of the project. This is due to the organisational, legal, financial administrative, environmental, and engineering problems all of which must be given detailed consideration prior to the construction of the irrigation works. The principal stages of a large irrigation project are: (i) the promotional stage, (ii) the planning stage, (iii) the construction stage, and (iv) the settlement stage.
The planning stage itself consists of three substages: (i) preliminary planning including feasibility studies, (ii) detailed planning of water and land use, and (iii) the design of irrigation structures and canals. Engineering activities are needed during all stages (including operation and maintenance) of development of an irrigation project. However, the planning and construction stages require most intensive engineering activities. A large irrigation project may take 10–30 years for completion depending upon the size of the project.
IRRIGATION FEASIBILITY PROJECT
A proposed irrigation project is considered feasible only when the total estimated benefits of the project exceed its total estimated cost. However, from the farmer’s viewpoint, an irrigation project is feasible only if his annual returns (after completion of the project) exceed his annual costs by sufficient amount. The feasibility of an irrigation project is determined on the basis of preliminary estimates of area of land suitable for irrigation, water requirements, available water supplies, productivity of irrigated land, and required engineering works.
PLANNING OF AN IRRIGATION PROJECT
Once the project is considered feasible, the process of planning starts. Sufficient planning of all aspects (organisational, technical, agricultural, legal, environmental, and financial) is essential in all irrigation projects. The process of planning of an irrigation project can be divided into the following two stages:
(i) Preliminary planning
(ii) Detailed planning.
Preliminary plans, based on available information, are generally approximate but set the course for detailed planning. Based on preliminary planning, the detailed measurements are taken and the detailed plans are prepared. Obviously, detailed plans are more accurate. Alterations in the detailed plans may be necessary at all stages of the project. The preparation of plans of an irrigation project in an undeveloped region is a complicated task and needs the expertise of specialists in areas of engineering, agriculture, soil science, and geology. The following are the main factors which must be determined accurately during the planning stage of an irrigation project:
(i) Type of project and general plan of irrigation works
(ii) Location, extent and type of irrigable lands,
(iii) Irrigation requirements for profitable crop production,
(iv) Available water supplies for the project,
(v) Irrigable (culturable) areas which can be economically supplied with water,
(vi) Types and locations of necessary engineering works,
(vii) Needs for immediate and future drainage,
(viii) Feasibility of hydroelectric power development,
(ix) Cost of storage, irrigation, power, and drainage features,
(x) Evaluation of probable power, income, and indirect benefits,
(xi) Method of financing the project construction,
(xii) Desirable type of construction and development,
(xiii) Probable annual cost of water to the farmers,
(xiv) Cost of land preparations and farm distribution systems, and
(xv) Feasible crops, costs of crop production, and probable crop returns.
Most of these elements of project planning are interrelated to some extent. Hence, the studies of the factors listed above should be carried out concurrently so that necessary adjustments can be made promptly as planning progresses
The preliminary planning of an irrigation project consists of collecting and analysing all available data for the current study, securing additional data needed for preparing preliminary plans for major project features by limited field surveys, and determining the feasibility of the proposed development by making the preliminary study of major features in sufficient detail. While investigations for the preliminary planning of irrigation projects should be conducted with minimum expenditure, the results of the preliminary study must be sufficiently accurate.
0 Comments