Tank irrigation, Mechanics of Tillage and Traction | Mechanics of Tillage and Traction Notes- Agricultural Engg - Agricultural Engineering PDF Download

The first census (1986-87) of Minor Irrigation schemes showed that there were 5,07,212 minor irrigation tanks in use in the country (excluding Rajasthan where no census was conducted). The southern region consisting of Andhra Pradesh, Tamil Nadu, Karnataka and Kerala, accounted for about 65 per cent of the irrigated area under tanks. (Table 24.1). Besides these, Madhya Pradesh, UP and West Bengal also have a large number of tanks in their respective States.

24.1 Tank Irrigation in South India

Tanks are a common feature of the south Indian cultural landscape and many were built in the 18th and 19th centuries by kings, zamindars and even the British rulers. Tanks are one of the important and oldest sources of irrigation and though they are found in all parts of India, they are concentrated in the Southern states of Andhra Pradesh, Tamil Nadu and Karnataka.

TABLE-24.1 Net Area Irrigated by Tanks in India, 1985-86

Unlike the northern region, the rivers in the south are mostly seasonal and the plains are not much extensive. Further, the geology is not favourable for groundwater storage. The local topographic variations have been effectively exploited to impound rainfall in tanks which are used to raise irrigated rice crops and simultaneously serve as means of improving groundwater recharge in their command areas. Tanks play vital role in the irrigation of Tamil Nadu where 20.4 per cent of the net irrigated area is watered through tanks. Andhra Pradesh (16.1%), Kerala (13.1%), Orissa (14.6%), and Karnataka (9.9%) in the Peninsular India and West Bengal (7.4%), Bihar (4.3%) and Rajasthan (0.77%) in the northern plains have sizeable net irrigated area irrigated through tanks. The area under tank irrigation increased from 36.13 lakh hectares in 1950-51 to 45.61 lakh hec­tares in 1960-61. Between 1970-71 and 2000-01 it declined from 41.12 lakh hectares to a minimum of 25.24 lakh hectares.

24.1.1 Andhra Pradesh

In Andhra Pradesh as many as eight districts are drought prone and tanks are the main source of water supply. Tanks were built in a series to avoid wasting water. The total number of tanks in the state during 1959-62 was 58,518 comprising 49711(85 per cent) irrigating less than 40 ha and the remaining irrigating more than 40 ha, However, the total number of tanks increased to 76,663 by 1988-89 with the addition of new tanks. Still, the number of tanks irrigating more than 40 ha has been reduced from 8,811 in 1955-56 to 7743 in 1986-89. Most of the decline in tanks is found in the drought prone areas of the state, where well irrigation is now the dominate source of irrigation. There was about a 28 per cent decline in the tank irrigated area between 1960s and 1980s, whereas well irrigated increased from 160,925 ha to 575,333 ha (i.e., 257 per cent increase) from 1959-62 to 1986-89.

24.1.2 Karnataka

Nearly 75 per cent of the Karnataka is drought prone and the state has about 36508 tanks of varying sizes with an irrigation potential of about 0.65 m.ha. The Malnad region (Shimoga, parts of Dakshina Kannada and Uttara Kannada ) has about 25 per cent of the total tanks in the state. Generally the tanks are small in size and harvest rain. Tanks in the Northern plateau (Belgaum, Dharwar, Bijapur, Bellary, Raichur, Gulberga, and Bidar) account for only 15 per cent) of the total tanks. In the Southern plateau (Chitradurga, Tumkur, parts of Chikmagalur, Hassan, Kadagu, Mysore, Mandya, Bangalore and Kolar), tanks are well distributed and account for 60 per cent of the total tanks. About 38 per cent of the tanks have a command area of less than 4 ha and large tanks with command area of more than 200 ha account for only about 1.4 per cent of the total number. Tanks with command area between 4 and 20 ha account for about 60 per cent and tanks with a command area between 20 and 200 ha account for about 10 per cent.

24.1.3 Tamil Nadu

There are more than 39,000 tanks in the State, of varying sizes and types. The tanks are classified into system tanks (which receive supplemental water from major streams or reservoirs in addition to the yield of their own catchment area) and non-system or rainfed tanks which depend on the rainfall in their own catchment area and are not connected to major streams or reservoirs. The tanks are also classified into Panchayat Union, PWD and ex-zamin tanks based upon the management authority. Panchayat Union tanks have a command area of less than 40 ha, and are under the control of village communities (Panchayat union). Those tanks having a command area of more than 40 ha as well as all the system tanks are maintained by PWD. Ex-zamin tanks were constructed by zamindars (landlords) during the British administration. After abolishment of zamindari system by the State government in 1957, they were transferred to Panchayat Union and PWD based upon the sizes of command areas. Out of the total of 39,000 tanks in the State, 53 percent are PU tanks, 22 per cent are PWD tanks and 25 per cent are ex-zamin tanks. There are about 9,800 ex-zamin tanks, of which more than 60 per cent are concentrated in the undivided Ramanathapuram district. About 9 per cent of total tanks are system tanks while rainfed tanks of the PWD, Panchayat Union, and ex-zamin tanks account for 13 per cent, 53 per cent, and 25 per cent of the total number of tanks in the State, respectively.

24.2 Classification of Tanks

Tanks are normally classified into system and non-system tanks. System tanks are those, which receive, water from nearby major streams or reservoirs in addition to the run-off from their catchment. Often these tanks enable farmers to raise more than one crop. Non-system tanks depend on rainfall and are not connected to a river system. Usually a single crop is raised under these tanks (Palanisami, 1981). Non- system tanks are often linked with the other tanks, thus forming a series of tanks. During times of heavy rainfall, the surplus water from upper tank will flow to the lower tanks. In the non-system tanks, the command to catchment area ratio may vary from 1:6 (in a high rainfall area) to 1:15 (in a low rainfall area). In system tanks, the ratio is smaller; and ranges train 1:2 to 1:5.

Tanks are also classified based on the size of command area or on the type of maintenance responsibility. Normally, after standardization, tanks are classified as major or minor tanks. Major tanks irrigate an area of more than 80 hectares and minor tanks irrigate less than 80 hectares. However, the maintenance responsibility is based on a different size classification. In Tamil Nadu, tanks of more than 40 hectares are the responsibility of the PWD while smaller tanks are under the control of Panchayat Unions for maintenance. About 7.300 tanks irrigate more than 40 hectares each, while about 31,900 tanks irrigate less than 40 hectares. Thus in numbers, small tanks are the most important to the state. The responsibilities for tank management also vary among the different states (Table -24.2). In all the states, the local village is responsible for water distribution and management of the tanks with a command area below 40 ha.

TABLE-24.2 Tank Management Responsibilities in Four Indian States

24.3 The issues of Tank Irrigation- Tamil Nadu experience

Tank irrigation, in certain parts of India, provides a good alternative for irrigation development. Tanks can have a wider geological distribution than large scale projects. Income distribution and employment generation effects are not limited to one area. Tank investments tend to be less capital intensive, have fewer negative environmental impacts and can better involve local communities in improvement and construction works. Currently the tank irrigation potential is under utilized due to problems relating to rainfall, poor tank structures, and lack of collective tank management.

24.3.1 Issues above the Tank Outlet

Siltation has reduced tank storage capacity by almost one-third. In the earlier days farmers used to de-silt the tanks using their bullock carts and manual labour to maintain tank storage capacity. This practice has become increasingly difficult to implement due to the lack of bullock carts and the decline in kudimaramathu (community repair work). The Government does not want to de-silt the tanks because of the cost and the difficulty involved in disposing of the silts outside the tanks. Furthermore in many tanks added capacity is needed in two out of ten years to store the surplus water. Thus in these tanks de-silting will only improve irrigation 20 per cent of the time.

In many tanks the supply channels which bring water to the tanks are heavily silted and in several cases they are missing due to the combined effect of siltation and encroachment. The use of illegal ‘pattas’ (rights from the government) to encroach on the tank foreshore is common and the run-off as well the tank storage capacity has been reduced. The encroachers drain the tank water when their crops in the tank foreshore are about to be submerged. They then argue with the Government that the tanks are not full most of the time and hence their right to cultivate the tank foreshore area should be sanctioned. Tank siltation is further aggravated by the deforestation in the tank catchment area both by the encroachers and the tank irrigators for fire wood. The end result is increase run-off and severe soil erosion during heavy rains. Simple procedure of closing the sluices during the rainy days, when there is no demand for water has been shown to increase the irrigated area by more than 20 per cent at a 17 per cent lower risk of crop failure. However, the present method of water distribution is continuous irrigation with sluices opened throughout the crop season.

 24.3.2 Issues below the Outlet

The command area of the tanks has been fixed based on the rainfall pattern, the number of tank fillings and the capacity of the tanks. After the introduction of the high yielding varieties of rice, the water requirement for rice has steadily increased. Thus the command areas are now too large for many tanks to serve effectively, given farmers’ emphasis on rice production. Many changes in cropping patterns have been recommended by the Department of Agriculture but few changes have occurred.

Due to inadequate tank water supplies for rice, particularly at the end of the crop season, there is a growing need for supplemental well irrigation. Currently about 15 per cent of the tank farmers own wells and there is a powerful monopoly market for groundwater in a number of tank irrigated areas. It was estimated that about 38 per cent of the crop income of the non-well owners is paid as water charges to the well owners in Tamil Nadu during 1992-93 (Palanisami, etal, 1997). Involvement of the farmers in the decision making processes concerning new tank construction and/or tank improvements has been very limited. This results in poor coordination between the Public Works Department (PWD) and the local communities in tank management.

Under the present two-tier system, the ownership and maintenance responsibilities for most of the tanks lies with the state Public Works Department (PWD) but the collection of water charges is the responsibility of the Revenue Department. There is practically no coordination between the two departments. The funds allotted by the revenue department to lank repairs and maintenance are highly inadequate. It costs about Rs 80 to Rs 120 per ha for the operation and maintenance of the tanks and the funds allotted for this purpose are only about As. 20 to 40 per ha. The water charges which are linked with the land revenue vary from Rs 80 to 90 per ha and are not allocated for tank maintenance by the revenue department.

24.3.3 Poor Water Distribution and Farmer Conflicts

The Government has the responsibility for developing water resources, but has little control over tank water distribution. The present system of water distribution is vested with the local villagers, sometimes village committees. The PWD does the major maintenance on tanks under its control such as the repair of tank bunds, tank sluices, and breaches above the main canal Outlet. Maintenance below the canal outlets primarily the responsibility of the farmers and the Panchayat Union. However, for some of the larger tanks, the PWD does maintain the main canals. In the case of tanks with less than 40 ha, the local Panchayat does the maintenance, with financing from minor irrigation grants (for non-standarized tanks) and from local irrigation grants (for standardized tanks) (Revenue Department, 1980).

Normally the water is released from the tank by a waterman (called Madayan Thotti) who is paid by the villagers in kind after the crop harvest. Their appointment is hereditary but the Waterman can be replaced if his service is inadequate. The appointment is made by local committees in the villages. The watermen also have responsibility for water use at the farm level, but their main job is to open and close the tank sluices as directed by farmers. Reliable statistics are not available concerning the volume of water in the tanks or the quantity used for irrigation. The usual assumption, which has continued for decades or even centuries, is that 85.8 hectares of rice can be irrigated during one crop season with one Mm3 of water. This figure is very low since more acres can be irrigated with one Mm3, particularly on heavier soils. The field to field irrigation practice results in heavy water losses. Water is normally drawn continuously from the tanks even when there is no apparent demand for water, that is, even on days of adequate rainfall.

Tank water user organizations have tended to be very weak and have received little support from the state or central government. A high variation in farm size appears to contribute to the poor cooperation among tank farmers. In such cases, the large-scale farmer with a strong asset position, usually have one or more wells and show little interest in contributing to tank management. The farm-size variation problem may be further compounded by the influence of local caste and political party affiliations. In large tanks, these factors are likely to make t difficult to agree on a common tank management strategy.

24.3.4 Multiple Uses and Property Rights

One of the key factors that have caused a misuse and excessive competition in tanks is inadequate institutional arrangements to guide their use including the lack of clearly defined, stable, and enforced use-rights. An example of this is the case of encroachers, who illegally cultivate in the tank foreshore area and pressure government officials into granting them the use of this land. This creates conflicts with the tank irrigated farmers, since the encroachers illegally open the sluices when the tanks begin to till during heavy rains tearing that their foreshore lands will be submerged.

It property rights are not completely specified, not exclusive, not transferable, or not enforceable; they likely give user incentives to misuse the resource. Insecure property rights prevent resource users from planning to use their resources efficiently over time because they cannot be certain they will retain access to the resources. This is clear in the case of encroachers, who often encroach and cultivate the fertile foreshore lands, but do nothing to improve the land or the catchment area.

Since in many tanks foreshore and catchment areas are mostly unmanaged, they are basically open access resources and subject to serious misuse. Insecure benefit streams due to uncertain property rights leads to little investment in tank management because potential contributors to tank improvement are certain of bearing the costs of improvement, but may not enjoy many of the benefits. Thus the expected private returns to investment are lower than the expected social returns. In the case of open access resource one individual’s use does affect the use by others. Since those costs are distributed across the entire community of users, they are ignored by the individual users and overexploitation of the resource results. When the open access situations exist individuals can exploit a resource without owning it. Under insecure property rights and encroachment, people who use resources may fear losing access to it, so they use it with a short time horizon in mind. Other examples include tank water, groundwater, common grazing lands, and fisheries that are overexploited in many of the tanks.

Incomplete property rights thus can lead to two closely related problems. First, people tend to over-utilise the resource because they obtain all the benefits but only bear a portion of the costs of drawing down the resource (stock effect). Second, people tend to under invest in maintaining resources with insecure property rights because they bear all the investment costs but may gain only a portion of the benefits. Low productivity and gradual degradation of such resources is likely to occur. Sometimes this is because traditional agreements regarding access to resources cannot be sufficiently enforced under current conditions. For example, even though farmers are eligible to remove silt from the tanks, they are prevented by the social forestry officials from entering into the water spread area. In other cases, incomplete property rights occur because governments replaced traditional property rights and working rules with others that are not applicable. For example, the Government replaced traditional property by supporting the social forestry in the poramboke (Government owned) land and in the tank water spread area. This has now been recognized as a mistake and the Government currently is discouraging plantations in the water spread area.