IRRIGATION AND POWER
ASSESSMENT OF WATER RESOURCES In India, as in other countries, rivers have had a powerful influence on national and local life. Successful agriculture in most parts of the country is not possible without the use of river waters. The large land resources of India cannot be put to productive use without a simultaneous development and use of the water resources. In fact, an integrated development of the land and water resources of India is of fundamental importance to the country's economy. From times immemorial, life and civilization in India have been dependent largely on rivers. The earliest civilizations developed along the banks of the Indus and the Ganga and their tributaries. In the Deccan, except for the narrow strip along the western coast, large parts of the population have depended for their existence on river waters.
2. Irrigation, or the artificial application of water to crops is an old art in India ; in many parts it began with agriculture itself. References to the practice of irrigation in India have been traced to many centuries prior to the commencement of the Christian era. The large numbers of tanks, which are found in the Deccan, have been in existence for ages. The Cauvery delta canals date back to the second century and the Yamuna canals were constructed originally about the 14th century. Under certain favourable conditions river waters provide a cheap source of power either directly or through the generation of hydroelectric power. In India, with little oil and coal deposits confined to certain parts of the country, hydro-electric power has an important part in her development. Apart from rivers, underground waters constitute an important source of water supply for domestic and agricultural purposes. The exploitation of sub-soil water resources must be integrated with the use of river waters.
3. Physiographically, India may be divided into four parts : the Peninsula proper, the Himalayas and associated mountains, the Indo-Gangetic alluvial plains and the Thar desert. The Peninsula is an ancient landmass owing its present features to denudation and weathering over long ages. It is composed mainly of ancient crystalline and metamorphic rocks. The western third of the Peninsula is covered by lava flows. Except for a fairly broad strip along the east coast and a comparatively narrow one along the west coast, most of the surface of the Peninsula is composed of hills and plateaus. The coastal plains are the most productive parts of the Peninsula. The Himalayas and associated mountain ranges of northern India are folded mountains of the tertiary age. The Indo-Gangetic plains lie between the Himalayas and Peninsular India and represent a sag or depression in the earth's crust which has been filled up with alluvium brought down by the rivers. They constitute one of the most fertile tracts in the world. The alluvial soil of these plains is being cultivated
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from times immemorial and shows little signs of exhaustion. The rivers flowing through the plains are snow fed, active during the rainy season and carry enormous detritus load. The Thar desert is an and region in the north-western part of the country. It occupies a large part of Rajasthan.
4. India lies partly in the tropical and partly in the sub- tropical regions of the world the Tropic of Cancer passes through the Rann of Cutch and the middle of West Bengal. The sub-tropical zone, comprising Rajasthan and the western part of the Indo-Gangetic Plains shows extremes of climatic condition, while the tropical zone is more equable. In most of the country, there are three seasons : (i) Winter : November to March ; (ii) Summer : April to June ; and (iii) Rainy season : July to October. The exact duration of each season, however, varies in different parts of the country.
5. The outstanding feature of the rainfall in India is its unequal distribution during the year and its variation from year to year in respect of quantity, incidence and duration. The average annual rainfall of India is 50 inches but it is only of the order of 5 inches in the desert in the north-west, increasing gradually across the plains of northern India from west to east until it is about 100 inches in Assam (see Figure 1). In central India, the mean rainfall is of the order of 50 inches a year, and in the Peninsula, except along the west coast, the mean annual rainfall is of the order of 30 inches. Almost the entire rainfall in the country is due to the south-west monsoon and is received during the four months of June to September, with the exception of the south-east portion of the Peninsula, where the rainfall is heavier from October to December. In winter the rainfall varies from 1 to 2 inches except in north-east monsoon areas, and from March till the onset of the south-west monsoon, the country is almost rainless. Apart from its unequal distribution in the year, the rainfall shows considerable variations from year to year. It is not uncommon in many places for rainfall in a year to be less than half the normal ; even one fourth of the normal during a critical period in the crop rotation has been experienced.
AVAILABLE WATER RESOURCES 6. The rivers of India may be broadly divided into two groups : (1) The snow-fed rivers of northern India, and (2) the rivers of central and southern India. The Himalayas give rise to three important river systems of northern India : the Indus, the Ganga and the Brahmaputra. The chief rivers of central and southern India are the Mahanadi, the Godavari, the Krishna and the Cauvery flowing eastward into the Bay of Bengal and the Narmada and the Tapti flowing westward into the Arabian Sea. The Chambal, the Betwa and the Sone drain the northern edge of the Peninsula and flow into the Ganga system.
7. The rivers of northern India, rising in the Himalayas, are snow-fed and flow all the year round though the supplies available in winter are low. The rivers rise with the melting of snows in spring and with the break of monsoons they swell further and carry enormous floods during the rainy season, the supplies falling again from October onwards. The rivers of central and southern India have no snow-fields at their heads and their supplies
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depend entirely on rainfall. Since this rainfall is confined to a small part of the year, the rivers carry large supplies in these months and the dry weather flow sometimes dwindles down to almost a trickle.
8. Detailed gauge and discharge observations are available for many of the major rivers in India for the last few decades. Most of these observation are however, mainly in connection with existing or projected irrigation works. There has been no attempt to make a complete hydrographic survey of the country; the task is one of great magnitude. The Indian Irrigation Commission of 1901-1903 estimated that the total annual surface flow in the rivers in India, (as it was then, but excluding Burma, Assam and East Bengal) was 51 billion cubic feet. This is equivalent to 1170 million acre-feet* of water. A more recent appraisal of the water resources of the country, based on an empirical formula co-relating the river flow in each basin with its rainfall and temperature, gives the total annual flow as equivalent to 1356 million acre-feet for the Indian Union. Of this only 76 million acre-feet or 5.6 per cent are at present being used for purposes of irrigation ; the rest flow waste to the sea. The position in regard to utilization of water resources in the important river basins is set out below:
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9. There are numerous other rivers and rivulets in which waters are available for utilization, mostly on an intermittent basis during the rainy season. On quite a large number of these, small irrigation reservoirs have already been built ; but many more can be constructed and there is an increasing activity all over the country to utilize the waters of these small streams.
10. Substantial water supplies for irrigation, industrial and municipal uses are available from under-ground waters. Wells have been constructed in all parts of India for domestic water supply and for irrigation of land and they are in use from times immemorial ; but large scale irrigation from this source is possible only with the help of tube wells operated by power pumps. No inventory of the ground water resources for the country as a whole has as yet been prepared. The information available indicates that ground water is generally available in all parts of the country, but it would be economical to tap it for large scale irrigation by means of power-driven tube-wells only in parts of Uttar Pradesh, Bihar, Punjab, Rajasthan and Gujerat.
WATER RESOURCES THAT CAN BE DEVELOPED FOR IRRIGATION 11. Water supplies for irrigation can be obtained from three sources :
(i) directly from the water normally flowing in rivers i.e.,by diversion Canals ;(ii) from storage of flood-waters flowing in rivers or directly of rain water from small catchments ; and (iii) from the waters available underground i.e., by wells or tube-wells. The extent to which supplies are available from the three sources mentioned above varies in different parts of India ; so also does the extent to which the available sources can be utilized economically.
12. The total quantity of water flowing in the rivers, a rough quantitative indication of which has been given in paragraph 8 above, is not wholly available or needed for irrigation.
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This is due mainly to the following reasons :-
(i) Over most of the country, rainfall is concentrated in a comparatively short period of 4 to 6 months. The rivers carry large volumes of water during this period, a great portion of which must go unutilized because it is neither physically possible to divert, nor economic to store, all but a small portion of this flow.
(ii) The volume of water, in the rivers, also varies greatly from year to year. Schemes of development, on the other hand, can be executed only on the basis of firm supplies i.e., supplies which would be available during most of the years.
(iii) In areas of high rainfall, like the west coast and north-eastern India, irrigation is either not necessary or is needed only to a very limited extent.
(iv) Certain quantities of water must be allowed to flow in rivers for hydroelectric development, for purposes of navigation, conservancy and water-supply for towns and villages.
It is difficult to state the percentage of the total river flow that can be used for irrigation. On the Cauvery, which is the most developed river in India, about 60 per cent of the annual flow is utilized. On the other hand, on the Brahmaputra the utilization is almost nil. While conditions certainly vary from river to river, it will not be far out to state that out of a total of 1356 million acre- feet of water, it should be possible to put to beneficial use about 1/3rd or 450 million acre-feet ; the existing utilization is 76 million acre-feet. It should be clear, however, that the extent to which river supplies can be put to further use is governed largely by the extent to which monsoon flows can be stored. Storage projects, by their nature, are more costly than diversion projects. There are, however, two important features of these projects which offset their high cost, viz., the possibilities of hydroelectric generation at the dams and the protection afforded against flood damage.
EXISTING DEVELOPMENT 13. Irrigation-A hundred years ago, about 1850, two or three million acres of land were irrigated by large numbers of indigenous irrigation works. These works were in the nature of small tanks in southern India, inundation canals in northern India and reconditioned canals like the Cauvery delta system in Madras and the Yamuna canals. About five million acres were under well irrigation at that time mostly in northern India. The first major irrigation work constructed in India was, the Ganga Canal in Uttar Pradesh, opened for irrigation in 1854. This was followed by the Upper Bari Doab canal in the Punjab and the Godavari delta system and the Krishna delta system in Madras. Then came the Sirhind canal in the Punjab, the Lower Ganga and the Agra canals in Uttar Pradesh and the Mutha canals in Bombay, the last named being from a storage reservoir. A number of other large irrigation works were constructed towards the end of the last and the beginning of the present century and again after the end of the first World War. Table 1 gives particulars of important irrigation works existing in the country and Table 2 shows important irrigation and agricultural statistics by States.
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14. Subsoil waters have been used in India for irrigation from time immemorial by means of ordinary percolation wells. During recent years, electrically driven tube-wells have opened- up a new method of utilising ground-waters on an extensive scale and in Uttar Pradesh, there are over 2000 State-owned tube-wells. Bihar, Punjab and some other States have also recently taken up the exploitation of ground waters for purposes of irrigation by tube-wells. Tube-well irrigation is generally more costly than irrigation by gravity canals from diversion projects. But for areas not otherwise commanded it is a useful means of irrigation in regions with good underground supplies.
15. It will be seen from Table 2 that India has a gross area of 812.52 million acres of which 491 million acres lie in Part `A' States and 322 million acres in Part `B' and Part States. Agricultural statistics are not available for the entire area of the country ; about 230 million acres which formed part some of the former " Indian States " have not yet been classified. Statistics are at present ,available for only 581 million acres of land and out of this 369 million acres are culturable. The area actually under cultivation in a year is 277 million acres. The area irrigated form all sources is a little less than 50 million acres or roughly 18 per cent of the total area sown in a year. Thus 92 million acres out of the classified area have yet to be developed in addition to large areas similarly awaiting development from out of the 230 million acres so far unclassified.
16. Navigation-Apart from the use of river waters for irrigation and power generation, for water supply and disposal of sewage, another important use is for purposes of navigation. At one time the rivers of northern India were the main arteries of communication. With the construction of railways, river traffic gradually fell off and inland water transport today is restricted to certain parts of Assam, West Bengal and Bihar. The waterways have also gradually gone out of use because of the withdrawal for purposes of irrigation of the bulk of the dry weather flow. In central and southern India, inland transport could not have been very extensive as the dry weather flow was not enough for navigation except by very small country boats.
Flood control-Although flood control cannot be called a water use, the problem of flood control can best be considered in relation to the existing development on the rivers in India. Every year considerable damage occurs from floods in different parts of the country. Until recently no regular statistics of this damage were collected. Whenever heavy damage resulted from a flood in the larger rivers, enquiry committees were set up and in some cases suitable flood control measures were undertaken. Extensive embankments have been constructed in parts of Assam, Bihar, West Bengal and Orissa. The problem of flood control is now always considered in conjunction with the construction of multi-purpose projects. The construction of large dams to store these flood waters is the most effective way of preventing flood damage.
Recreation-Rivers, natural and artificial lakes and large canals provide important places of recreation for the people. Some of these sites are potential centres of tourist traffic. Fish Culture-Large collections of water and regulated river flow provide excellent facilities for fish culture. Some of these have been developed but not on any large scale.
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ASSESSMENT OF POWER RESOURCES 17. Sources of power can be divided broadly into two classes-(i) exhaustible or those which represent accumulation of energy, gradually formed under the action of the sun's light and heat, e.g. coal, mineral oil, peat, natural gases ; and (ii) inexhaustible, or those which are replenished by nature as fast as they are utilized, e.g. water falls, winds and tides.
The production of power from sources like tides and winds is by its nature limited. Among the fuels derived from growing vegetation, alcohol, which can be manufactured from molasses, mahua flowers, etc., alone has good prospects in India. Projects for increased production of alcohol are dealt with elsewhere in the report. Until atomic power and solar energy come into the field, the development of power resources in India can only be from coal, oil and water.
18. India's reserves of coal have been discussed in Chapter XXVII of the Report. It will be seen that out of total workable reserves estimated at 20,000 Million tons, good quality coal is only 5,000 million tons. This has to be conserved for important metallurgical and other operations in which the use of good quality coal is indispensable. There art, however, large reserves of low grade coal available which it is now possible to utilize for steam generation in suitably designed furnaces. This opens up a new source of supply for electric power generation by burning lignites (available in large quantities in South Arcot district and in Cutch) and other coals of high ash content which were hitherto considered to be unuseable for this purpose. It is however, obvious that on account of the high inert content of these coals, their transport over long distances cannot be economical and these can be used for power generation only in areas in which they occur.
India's wealth of coal is confined to Bihar and, West Bengal with small outliers in Assam, Madhya Pradesh and Hyderabad ; large deposits of lignites occur in South Arcot district in Madras and in Cutch. The distribution is uneven and distances from the coal field to industrial centres are so great that except at or near localities where coal mines exist thermal generation of power may often prove uneconomic. Resources of petroleum, so far as known, are small. There is only one field in Assam which produces about 5 per cent of the total requirements of the country ; the remaining 95 per cent of the consumption has to be met by imports.
19. India's resources of hydro-electric power are vast. These resources have not even been surveyed in their entirety. A committee was appointed which issued a preliminary report in 1919 and a final report in 1921 and indicated a minimum continuous water power potential in India of 3.5 million kW. This, however, is proved to be an under-estimate. Projects not included in that survey have since been taken up for investigation and some of them are in an advanced stage of development. There are no doubt other sites which have not yet been taken up for investigation. The total hydropower potential of India may be UP to 40 million kW.