Dossiers en cours
2008 / 2009
dph participe la coredem
11 / 2009
Found all over the Dravidian land in the Indian state of Tamil Nadu, tanks offer much more than agriculture. These tanks have been historically linked to the progress of communities and civilisations. Presently, they are swaying for survival. Their proper functioning is important to support the ever-increasing population.
The landscape of southern India is dotted by about 140,000 tanks that have been the backbone of the irrigation system for centuries. Over time, and modernisation, most of the tanks have gone into disuse. Due to poor management, the gross area irrigated by them has come down from 4.78 million hectares to 3.07 million hectares though new tanks were constructed during this period. The share of tanks in the net irrigated area decreased from 18.50 per cent in 1960-61 to about 7 per cent in 1990-91 at all-India level while it has declined from 38 per cent to about 23 percent in Tamil Nadu. In Tamil Nadu, some of the tanks are still functioning while some are being revived. Most of these tanks supply channels. They are in a dilapidated condition due to encroachment, scrub jungle formation, contract lands, and agricultural activities within the tank area, siltation and breached channel banks. This has resulted in the reduction of their water harvesting and carrying capacity.
Definition of a water tank
A tank is a human made or natural reservoir of water containing earthen bunds or embankments. River or rainwater runoff from the catchment empties into the tank. The tanks are non-system and system tanks. Non-system tanks are those tanks, which receive their water intake from the rain and have a small storage capacity. They have an area of less than 40 hectares and the minor irrigation department of the government is responsible for their management. System tanks are fed with water from rivers and runoffs through diversion weirs, feeder channels and surface flow. They may be linked as cascades where water from one upper tank flows into the lower tank.
Some of these chains of tanks are now functioning as isolated cases. These tanks irrigate many ayacuts (agricultural command areas) spread over multiple villages, and across various government administrative zones. The tail-end region of a tank is the catchment of the next tank in the series. A tank has a surplus weir that allows excess water to flow out preventing the breaching of the bund. There are sluice gates that divert water from the tank to the main irrigation canal. From the main irrigation canal within an ayacut, the water is diverted to fields through branch canals. The accessories consists of water bodies, tank structures, feeder and supply channels and canals, wells, wetlands, semi-dry tank fed lands, soils, plants, animals, birds and fishes making it one of the oldest eco-systems.
These culturally associated tanks accompanied well-organised village institutions to maintain and manage them. The social activities of management and maintenance survived across thousand years before the colonial rule set in. Then came the Indian government who also followed colonial legacy of central control. The locals lost interest and the situation turned grim. Isolated efforts were always made to maintain them.
Management of tanks
In the past…
One of the most phenomenal elements of tank systems is its management. There are multiple stakeholders – the government, farmers, landowners, local organisations – all have a say or a piece in their management. Water has to be allocated to various ayacuts, some large, some small, conflicts arise and they have to be solved. Historically, these tanks were under the control of rich zamindars (landlords) and mirasidars (big landowners) who used to form informal groups to enforce kudimaramati system. The village community, the kudimaramats (user) were expected to contribute labour for upkeep and irrigation maintenance. But the British brought the change in land tenure under the Ryatdari (land tenure) system, because of which the mirasidars lost their power to maintain tanks as these tank now were part of government property. Regulated rules for water distribution were maintained by mamoolnamas (record keepers) in a recorded form and this system deteriorated.
After independence, these tanks passed on to government departments. The public works department (PWD) is responsible for management and maintenance of all system tanks and non-system tanks with areas of more then 40 hectares (ha) tank area. The tanks have immense potential but due to lack of proper maintenance and inconsistency in grant allocation, the utilisation factor is less. The small tanks with area less than 40 ha are being taken care of by the panchayats (local village administrative body) and are called erie panchayats. The PWD appoints neerkatti (waterman) to supervise the tank water supply. These neerkattis are appointed from villages and they are paid with a share of the crop from the ayacuts. The ayacutdars are responsible for the maintenance of inlet channels, tank bed, tank bund, surplus weirs, sluices and associated structures.
Recently, the trend of forming water users association (WUA) at the tank sluice level or in the village level has also started. The WUA is responsible for the maintenance and management of the tanks.
Sharing of water
Water in most cases is allocated to the villages within an ayacut jointly by the PWD and the irrigation board (IB). The tanks have superintendents who are assisted by a number of laskars (lower level clerks in the PWD). The superintendent is responsible for opening the vents of the surplus, and the waste weirs once the water level rises above the sill level. Vents are kept open to allow water into the tank from the river as long as the level does not fall below the sill. The superintendents have to ensure that the water reaches the tanks from its sources without any hindrance and that all the weirs are provided with vents, and the sluices are well maintained. The authority has to see that all trees along the bank of the channel and the bunds are cut. This is done to maintain a 1.8 m path and a clear headway of 3.4 m. The pathway is needed for the laskars to clear silt and carry other repair works.
The opening and closing of the sluice determines the allocation of water among the different segments of the ayacut of each tank. Requirements of the villages determine the opening and shutting of sluices. Supply is released on the basis of yadas – a written slip, for release of a specified quantity of water to the ayacut, given by the village representative to the secretary of the irrigation board or to the junior engineer of the public works department. The decision to open or close the sluices is made by the PWD in consultation with the irrigation board or the tank farmers association (TFA). Nobody can make independent decisions. Once the sluices are opened, they won’t be closed even after the rainy season is over. All villages get a continuous supply till the third season. The availability of water in the third season depends on village’s distances from the tank and on the height of the sluices. The low sluices are served first, followed by the middle and the higher sluices. In some cases, the high level sluices don’t get water until the tank is full. When the storage is poor, then the low-level sluices are opened depending on priority. Head reach regions served by the lower sluices gets the maximum supply. Higher sluices get limited water for a limited duration. This leads to the cultivation of single crop only even when the tank is at full level.
After a sluice is opened, it is not closed till the ayacut receives heavy rainfall. Water flow is continuous. From the main channel, water is diverted to individual villages by masonry structures and diversion vents. These structures are made on the procedures of the mamulnamas. In order to prevent abuse of the supply channel, kamukotties and thotties are appointed by the villagers in the middle reach and tail reach villages. In some cases, there are two types of rationing – automatic regulation and supervised regulation.
In the automatic system, the water flows to the irrigation channel when the tanks supply is released into the main channel. Rationing of water is adopted at the main and the branch channel level by constructing a permanent structure to divert water in the required proportions.
Under the supervised system, the neerkatties and kammukotties of the respective village or channels regulate supply in a main or branch channel. For e.g., in the Moolai sluice of the Kaveripakkam tank system, there are three points where the regulation is supervised. Each point serves two channels. One of the channels irrigates for 30 naligai in the daytime while the other irrigates at night for the same duration. The kammukotti or thotti has to be present when the water is released. Irrespective of the ayacut is fully irrigated or not, only 30 naligai will be allowed. Supervised supply is found in one of the sluices of the Kaveripakkam too. Under one method, two hours (4 am to 6 am) is diverted to irrigate the ayacut in Kondapuram village. From 6 pm to 8 am, water is diverted into the Theyradi channel. In the remaining 20 hours, a foot deep supply is diverted to Kondapuram.
The main channel of Athipattu has another method of regulation. Kammukutties divert full supply water from 6 am to 6 pm to Athipattu. From 6 pm to 6 am, next day, the supply is diverted to Sirukarumbur. Vilaham village also gets water for 12 hours but on alternate days. This system has uninterrupted supply for 12 hours. When the water reaches the villages, the farmers follow customary rules to allocate the water among the different community members.
When there is enough water, all the network channels supply water simultaneously. All the farmers take any amount of water they want. This is a wasteful method, but generally followed in case of high water supply. The problem arises when there is a shortage of water.
During periods of scarcity, the farmers practice murai which is fixed time bound rationing of water. The water is distributed through one branch channel at a time through rotation. Villages that are supplied by lower level sluices do not practice murai as the supply situation is better. When murai is in force, a maximum of 30 to 40 per cent per acre (1 acre = 4000 square metres) of ayacut can be cultivated. If three days of water supply were allotted for one village, then, in 72 hours, it would get seven minutes by which it would irrigate an average of 255 ha, each acre getting water for 7 minutes. The duration of supply is fixed. This type of system is followed mainly in the tail-end villages of the Kaveripakkam.
The farmers are free to decide whether to sow a crop or not. They decide the crops to be sown also. Individual farmers decide on crops depending on the water availability. In this case, farmers having private wells are at an advantage as they can sow crop without depending on the water from the tank.
These tanks have served these vast domains of agricultural tracts for centuries now. The negligence of the tanks increased the digging of wells whose number multiplied. This has depleted the groundwater table. There are chances of increase in salinity in the ground water. The presence of many industries like tanneries has already contaminated the surface water and groundwater sources in many parts of Tamil Nadu.
The maintenance of the tank is not enough to provide water for agricultural activities. If the catchment is neglected, drought situations may arise in certain parts. Tamil Nadu receives good rain. This has to be tapped and stored in the tanks. The tanks cannot depend only on perennial and non-perennial sources when there is a huge runoff available.
These tanks are community assets and they have to be completely responsible for the whole system. Institutional mechanism performing from the village level is very important. The government can pass the tanks under the control of the villagers, as was originally. The performance will be further enhanced. Government can act as the boost in the process with guidance and financial help.
The approach has to be holistic with complete participation of all stakeholders. It is important to include other aspects related to the tank like fisheries, and tourism also. Then a tradition can become strong to support the farmer, the community, an economy, an ecosystem, an institute, and a state.
This sheet is available in French: Les cascades de réservoirs d’eau au Tamil Nadu
K. PALANISAMI, « Reconciling with the private wells in the tank community », in Anil Agarwal et al (eds), Making Water Everybody’s Business, Centre for Science and Environment, New Delhi, 2001
R. SEENIVASAN, T. SENTHILKUMAR, N. KARUPPUSWAMY, « Hydrology of Tanks in Vallakulam Cascade », in Tank Cascade, DHAN Foundation, Madurai, Vol.1, No.1, 1999, pp. 1-7.
S. Martin SELVERAJ and N. VENKATESAN, « Encroachments and Evictions in Tank Systems: A Case study of Athikarikulam Tank in Theni District », in Tank Cascade, DHAN Foundation, Madurai, Vol.1, No.2 & 3, 1999, pp.31-40.
S. Martin SELVERAJ and M. P. VASIMALAI, « Sharing the Tank Water: Type and Issues in Vallakulam Cascade », in Tank Cascade, DHAN Foundation, Madurai, Vol.1, No.1 1999, pp. 21-26.