It is known fact that India has a very large population and different studies show that it will continue to rise at least till 2050 A.D. The United Nations publication “Sustaining Water - An Update”, published in 1994 indicates that the population of India by that time could vary between 1349 million (low projection) and 1980 million (high projection), with a medium projected figure as 1640 million. At present the country’s food grain availability is around 523 grams per capita per day (though it varies significantly with the economic level). In China and USA, the corresponding figures are 980 grams and 2850 grams respectively. Assuming a population figure of 1800 million by 2050A.D, and a small rise in per capita consumption of food grain at about 650 grams, the annual requirement of the country would be around 430 million tonnes. The present productivity of irrigated land is about 2.5 tonnes/hectare and les than 0.5 tonnes/hectare for rainfed lands. Assuming that these levels can go up to 3.5 and 1.0 T/hr respectively by 2050 AD (which should be the urgent needs that has to be addressed to by the water resource engineer), it is imperative that the irrigation potential of at least 130 million hectare is created for food crop alone and 160 million hectare for all crops to be able to meet the demands of the country by 2050 AD.
Since the land and water resource of any country is not going to change much over the years, the water resource planners have to make cautious decisions on optimizing the available resources for maximum benefit. In the next section, we look into the options available and the decisions that may be taken.
Sustainable development in Irrigation
For the survival of the country, there is an urgent need to implement and plan irrigation strategies for now, and in future, as the population continues to grow. But that should not be at the cost of degradation of the present available resources of land and water, which means the natural resources that we have, should more or less remain the same after 50 or 100 years and beyond. This concept is termed “sustainable”, which was not much of a problem earlier when compared to the resources the demand was less. But now it is reversed and for devising any planning strategy the constraints have to be kept in mind. As an example, the utilization of ground water may be cited. In many regions of India, there has been alarming withdrawal of ground water for meeting demands of irrigation and drinking water demand than that which can be naturally recharged. This has led to rise of further problems like arsenic and fluoride contamination. Since ground water recharge by natural means takes a long time, perhaps years and even decades, there is little hope of regaining the depleted table near future.
Next we look into the options available to the irrigation engineer for development of irrigation facilities within the constraints.
The question that is to be resolved is this: Are we capable of producing the required amount of food grain for the country? Apart from spreading the network of irrigation system further into the country, there is an urgent need on research- for better seeds, better water management and distribution practices, low cost fertilizer etc., Nevertheless, the possible options available to water resource engineer to meet the future irrigation and food requirement may, therefore, include evaporation control and reduction and losses during conveyance of water through channels, recycling of water, inter basin transfer, desalination of sea-water in coastal areas, rainfall by cloud seeding, improved technology, etc. Loss of top soil due to erosion in one of the forms of degradation which can be contained on a limited scale but problems of salinity, alkalinity, water logging, etc. reduce the productivity. The future lies in considering and bringing under cultivation additional area and considering intensified production on existing good agricultural land and water resource system optimization.
Constraints of land and water
The total geographical area of land in India is about 329 million hectare (M-ha), which is 2.45% of the global land area. The total arable land, according to an estimate made by the Food and Agricultural Organization (FAO), made available through the web-site Aquastat, is about 165.3 M-ha which is about 50.2 % of the total geographical area (the average world figure is 10.2%).
India possesses 4% of the total average annual run off in the rivers of the world. The per capita water availability of natural run off is at least 1100 cubic meters/yr. The utilizable surface water potential of India has been estimated to be 1869 cubic kms.but the amount of water that can actually be to put to beneficial use is much less due to severe limitations imposed by physiographic, topographic, interstate issues and the present technology to harness water resources economically. The recent estimates made by the Central Water Commission indicate that the water resources utilizable through surface structures is about 690 cubic kms only (about 36% of the total ground water is another important source of water).
Ground water is another important source of water. The quantum of water that can be extracted economically from the ground water aquifers every year is generally known as ground water potential. The preliminary estimates made by the Central Ground Water Board indicate that the utilizable ground water is about 432 cubic km.thus the total utilizable water resource is estimated to 1122 cubic km. It must be remembered that this amount of water is unequally spread over the entire length and breadth of the country.
Of the total 329 M-ha of land, it is estimated that only 266 M-ha possess potential for production. Of this, 143 M-ha is agricultural land. It is estimated that 85 M-ha of land suffers from varying degrees of soil degradation. Of the remaining 123 M-ha, 40 M-ha is completely unproductive. The balance 83 M-ha is classified as forest land, of which over half is denuded to various degrees.
It is alarming to note that the percapita availability of land is half of what it used to be same 35 years ago. This would further reduce as our country’s population continuous to grow. At present 141 M-ha of land is being used for cultivation purposes. Between 1970-71 and 1987-88 the average net sown area has been 140.4 M-ha. The need for production of food, fodder, fibre, fuel in the crop growing areas have to compete with the growing space require for urbanization. The factors of land degradation, like water logging, salinity, alkalinity and erosion of soils on account of inadequate planning and inefficient management of water resources projects will severely constrain the growth of net sown area in the future.
Benefits of irrigation
With the introduction of irrigation, there have been many advantages, as compared to the total dependence on rainfall. These may be enumerated as under:
Classification of irrigation schemes
Irrigation projects in India are classified into three categories –major medium & minor according to the area cultivated the classification criteria is as follows:-
The ultimate irrigation potential of the country from major and medium irrigation projects has been assessed as about 64 M-ha. By the end of the ninth plan period, the total potential created from major and medium projects was about 35 M-ha.
Major and medium irrigation projects vis-à-vis minor irrigation projects
While formulating strategies for irrigation development the water resources planner should realize the benefits of each type of project based on the local conditions. For example, it may not always be possible to benefit remote areas using major/medium projects. At these places minor irrigation schemes would be most suitable. Further, land holding may be divided in such a way that minor irrigation becomes inevitable. However, major and medium projects wherever possible is to be constructed to reduce the overall cost of development of irrigation potential.
According to the third minor irrigation census carried out in 2000-01, there are about 5.56 lakh tanks in the country, with the most occurring in the following states
Due to non use of these 15 percent tanks nearly 1 M-ha of Irrigation potential is lost. Another, around 2 M-ha of potential is lost due to under utilisation of tanks in use. Loss of potential due to non use is more pronounced in Meghalaya, Rajasthan and Arunachal Pradesh (above 30%), whereas loss of potential due to under utilisation is more than 50 percent in case of Gujarat, Nagaland, Rajasthan, A&N Island and Dadar and Nagar Haveli.
It also appears that the maintenance of the tanks has been neglected in many parts of the country and their capacity has been reduced due to siltation. It has been estimated that about 1.7 M-ha of net area has been lost under tank irrigation due to drying up of tanks and encroachment of foreshore area. Some advantages of minor irrigation should also be kept in mind. These are: small investments, simpler components, labour intensive, quick maturing and most importantly it is farmer friendly.
On the other hand, it is seen that of the assessed 64 M-ha of irrigation potential that may be created through major and medium projects, only about 35 M-ha have so far been created. Hence a lot of scope for development in this sector is remaining. These may be realized through comprehensive schemes including storage, diversion and distribution structures. Some of these schemes could even be multi-purpose thus serving other aspects like flood control and hydro power.
Outlook of the national water policy
Our country had adapted a national water policy in the year 1987 which was revised in 2002. The policy document lays down the fact that planning and development of water resources should be governed by the national perspective. Here we quote the aspects related to irrigation from the policy.