Water has become a scarce resource, both in urban and rural India. Therefore, rainwater harvesting has become an urgent necessity. In rural areas, rainwater harvesting is done through surface storage bodies. The most important of such storage bodies are the traditional systems of surface water storage, called eris in Tamil, kere in Kannada, cheruvu in Telugu and a variety of other names elsewhere in the country.
These eris have played a very important role in providing water for agriculture in rural societies in regions with relatively low rainfall. Unfortunately, these systems, which have served our society for centuries if not millennia and are functional even today, are in a neglected state.
Time and again, the importance of surface water bodies has been recognised. In practice, policies have favoured the development of groundwater in the form of wells and borewells. Compared to groundwater, surface water is a renewable resource. And surface water bodies play a very important role in the recharge of ground water. Hence, even if groundwater is to be used on a sustainable basis, the maintenance of surface water bodies becomes very important.
Traditionally, eris have played a very important role in irrigation and the local ecosystem in areas with relatively low rainfall, such as large parts of Karnataka, Andhra and Tamil Nadu. These eris are located mostly in parts of India that receive an annual rainfall of 1,000 mm or less. Over the last 50 years or more, the contribution of eris in the area irrigated in our country has declined steadily. This points to a policy of neglect of these community-owned and managed structures in favour of individually owned wells.
Not only are eris marvellous examples of indigenous engineering skills and ingenuity, they also illustrate an understanding of nature and a sound and ecologically sustainable intervention in nature. An understanding of this technology and its relevance for today will go a long way in providing ecologically sustainable alternatives to the current mode of modernisation and development.
What is an eri?
An eri is a reservoir of water contained behind earthen bunds or embankments. Usually, the bund surrounds the water on three sides. The fourth side is open to the catchment from which the water flows down to collect in the eri. Normally, the middle of the bund is the deepest portion of the eri and the depth decreases as we go to the sides or flanks of the bund.
One of the main functions of an eri is irrigation of fields for agriculture and each eri is designed to irrigate a certain extent of agricultural land known as the ayacut of the eri. The water reaches the fields with the help of gravity, across (below) the bund through openings or valves called sluices (madhagu in Tamil). Normally, there are fairly elaborate arrangements for opening and closing of the sluices, which can be operated from the top of the bund. An eri has, depending on its size, a number of sluices. They are located at different levels so as to be able to supply water to fields at different elevations.
In India, agriculture depends upon and closely follows the monsoons (Southwest and Northeast), which are regular occurrences. Water conservation and irrigation technologies such as eris, took on the supplementary role of adding to the sufficiency, certainty and predictability of water availability for agriculture.
Where rainfall was relatively low, every effort was made to retain all the water that fell on the ground through appropriate water retention and conservation strategies. Since eris are local resources, the estimates of water available in them are constantly made by the village communities, which are used to make sure that the most efficient use of available water is made.
Traditionally, eris have played several roles:
1) As appropriate irrigation devices in the cultivation of paddy. Paddy is a highly location-specific crop, which is the reason why there were perhaps a couple of lakhs of paddy varieties all over India. Data from different parts of Tamil Nadu for the late 18th and early 19th centuries reveal that under eris, the productivity of paddy was considerably high and in fact higher than the yields in the 1960s. It is indeed important to understand how this was possible.
2) As a system that acted as a flood control device, thus preventing soil erosion and wastage of runoff water during periods of heavy rainfall.
3) As storage devices that acted as insurance against low rainfall periods and also recharged groundwater in the surrounding area.
4) As a device that was crucial to the overall ecosystem.
The Indian civilisation seems to have placed a great value on the decentralisation of resources and political power, which automatically set a limit to the size of irrigation structures. Large-scale systems such as modern dams would not have been compatible with the values and goals of Indian civilisation. The traditional irrigation technology of eris were also the ecologically optimal solutions for the natural conditions occurring in some parts of India.
T M Mukundan
Yoga instructor & Ayurveda scholar; founding trustee of Centre for Policy Studies