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

Introduction

A well is a small hole dug in the ground from which sub-soil water is taken out for irrigation and drinking purposes. An ordinary well is about 3 to 5 metres deep, but can reach up to a depth of 15 metres. It is a cheap, dependable and a popular source of irrigation in the country. It has been used in our country from time immemorial. Well irrigation is widely practiced in those areas where sufficient groundwater is available. Such areas are in Ganga Plain, the deltaic region of Mahanadi, Godavari, Krishna and Cauvery rivers, parts of Narmada and Tapi valleys and some parts of Deccan Trap. Greater part of peninsular India is unfit due to hard rocky structure and shortage of underground water. Brackish groundwater is also unfit for irrigation and human consumption.
Tube wells are, today, the most popular source of irrigation in India. The first tube well was sunk in 1930 in Uttar Pradesh. Today there are more than 50 lakh tube wells operating in different parts of India. Uttar Pradesh has the largest number of tube wells in the country. Tube wells are generally popular with rich and medium farmers. More than half of the net irrigated area is irrigated by wells and tube wells in the states of Bihar, Gujarat, Madhya Pradesh, Maharashtra, Punjab, Rajasthan, Haryana, Tamil Nadu and Uttar Pradesh. Well and tube well irrigation has contributed substantially for the success of Green Revolution in India. Source wise net area irrigated and number of wells energised was given in tables 27.1 & 27.2 respectively. It could be observed that there are 15674673 wells in India irrigating, 37.78 Mha, more than 60 per cent of the net irrigated area in the country. Uttar Pradesh has the largest area under well irrigation. It is followed by Rajasthan, Madhya Pradesh, Punjab, Gujarat, Maharashtra and Bihar.

Table 26.2  Irrigation Pumpsets Energised and Electricity Consumption in Agriculture Sector during 2007-08 by Region/ State

Drilling of private shallow tube wells is the only way in which groundwater can be developed in most of the hard rock areas of India, as in Madhya Pradesh. In these areas small local aquifers exist in fissured rock. In areas having alluvial aquifers, as in the north-eastern Gangetic plain and in Gujarat, other water lifting devices can be used as well. In practice, private groundwater development can only be undertaken (a) where the aquifer is shallow enough to use a simple water point and (b) where farmers have the financial resources to invest in their own irrigation system.

A tube well is generally more than 15 metres deep. The water is lifted with the help of a pumping set. The following factors favour the installation of a tube well.

1. There should be enough groundwater, as a tube well can irrigate about 2 hectares per day against 0.2 hectares by an ordinary well.

2. The water level should be between 15 m and 50 m, otherwise the cost of lifting the water will be very high.

3. The power, i.e. diesel or electricity should be readily available, so that water can be taken out at the time of need.

4. The soil should be fertile and can produce enough to meet the cost of irrigation by a tube well.

26.1 Types of wells

The utilization of groundwater through dug well irrigation is an indigenous form of irrigation. A dug well is a shallow well, with its bottom on a fair depth below the water table, so that water from the surrounding aquifer accumulates in the well. Water collected in the well is lifted to ground surface through a water lift. The masonry lined dug well usually yields 7 to 8 m3 per hour (@ 2 1ps) when operated with a Persian wheel, which is the case for about 20% of the masonry wells. In the remaining dug wells, the water is lifted by animal power with leather or metal buckets, usually bullocks. These wells have very limited discharge rates and this practice is almost dispensed with due to high cost of labour and drudgery.

Shallow tube wells are drilled to penetrate a shallow aquifer and are usually less than 30 m deep. This depth is only possible when the tube well is placed at the bottom of a dug well, so that it is a dug-cum-tube well. Shallow tube wells are usually equipped with a small centrifugal pump. The filter point wells if Cauvery delta of Tamil Nadu in Trichy, Thanjavur, Thiruvarur, Nagapatinam districts are shallow tube wells irrigating individual farms. The electric or diesel motor is directly connected to the pump by a belt drive. The centrifugal pump is placed at the surface level and operates mainly in suction mode. These wells usually have a capacity of 20 to 30 m3h-1 (@ 7 lps).

Medium tube wells are small diameter submersible tube wells equipped with a strainer section. These wells are usually about 45 m in depth although they may be deeper depending on the depth of the aquifer and the capacity desired. They usually have capacities of about 30 to 40 m3h-1(@ 10 1ps) and are equipped with centrifugal pumps. Water distribution from these wells is through small unlined channels with the following lengths: masonry wells - 30 m; shallow tube wells - 200 m; and medium tube wells - 400 m.

Deep tube wells have a large diameter and vary in depth from 40 to 300 m. Pumps are sunk into the well, operate in force mode, and are driven by submersible electric engines or by shafts connected to engines at the surface. Deep tube wells have a large discharge capacity varying from 150 to 300 m3h-1 (40 to 80 lps). As discharge capacity increases, the length of the water distribution channels increases accordingly. For example a command area of 100 ha is served by water distribution system of 4 km in state tube well commands of UP, water is distributed through unlined earthen channels.

26.2 Case study of UP

The greater part of Uttar Pradesh belongs to the Gangetic Plain which mainly consists of alluvial sediments. No bedrock occurs to a depth of 250 m and there is some evidence that locally the alluvial strata extend down to thousands of meters. Based on topographical features the following soils are distinguished (1) recent alluvial soils (2) soils of flat lands (3) upland soils and (4) lowland soils. Texture of these soils varies from coarse sands to fine clays. Over centuries river inundations have created a heterogeneous pattern of depositions of mainly medium to fine sand with additional clay and silt deposits. The upper 250 meter is composed of clay, silt, fine to medium sand and kankar. Kankar is an Indian term for a calcium carbonate nodule. Such nodules are associated with the occurrence of a hard calcium carbonate layer, or called Kankar layer, at some depth in the soil profile. The medium and fine sand layers are local aquifers separated by clay and silt layers. These small aquifers are phreatic and semi-confined. These local aquifers are interconnected and are part of a regional aquifer system, which is a thick highly productive phreatic aquifer.

The water table is subject to seasonal fluctuations. In April-May the water table in the project area is usually at its lowest level between 4 to 8 meters below soil surface. During monsoon the water table generally reaches 2 to 3 meters below soil surface. In large areas of the project after monsoon the water table falls rapidly to 3-4 meters below soil surface. This is followed by a more gradual decline during the rest of the dry season. In the areas with groundwater levels at 4 to 8 meters below soil surface, groundwater extraction by shallow wells is technically possible. In some areas of the districts Faizabad, Sultanpur, Ballia and Bahraich the pre-monsoon water table is as low as 14 to 15 meters below soil surface, and rises during monsoon to about 8 meters below soil surface. The deeper water tables in these areas may be due to a relatively higher elevation of the area as well as a higher groundwater abstraction in combination with a relatively low recharge. In these areas, having a deeper water table, water can only be extracted through submersible pumps.

Irrigation from public tube wells is practiced from 1935 onwards and the Government of Uttar Pradesh invested in the construction of State or public tube wells. In 1940 some 1,471 public tube wells were in operation, serving a gross irrigated area of 240,000 ha. The number of public tube wells expanded slowly. By 1950 around 2,000 public tube wells were in operation, irrigating some 360,000 ha gross. The program was then accelerated, which doubled the served area to about 730,000 ha gross in 1960. The importance of private tube wells for irrigation was negligible up to the 1960s. The benefits generated by the private tube well investment increased in the 1960s because agriculture became more intensive due to the introduction of the Green Revolution technology. The area under private wells increased rapidly from some 50,000 ha in 1960 to about 4 Mha in 1980. Performance of public tube wells declined. Though the number of public tube wells in operation doubled between 1970 and 1980, the irrigated area served by public tube wells hardly increased. By 1980, some 17,000 public tube wells were in operation, covering a net irrigated area of 776,000 ha. So compared to 1960, the situation in 1980 was completely reversed. Instead of public tube wells, privately managed tube wells were the most important technology in exploiting UP'S groundwater resources. The greater part of the increase in private tube wells took place in the western part of the state, which is wealthier than the eastern part.

26.2.1 Improved design of public tube well systems

The water supply of the public tube well would not meet the crop water requirements to its fullest extent in the command area. The total cultivable command area of 100 ha was served by a deep tube well with a discharge of 150 m3h-1 or 0.42 1ps/ha. The public tube wells have an average depth of 65 to 90 m. Within this depth some 30 to 40 m of medium sand could be found. With a screen of 200 mm diameter, this aquifer would yield water for a tube well capacity of 150 m3h-1. It was assumed that power constraints would limit daily operation to about 16 hours, therefore average discharge was expected to decrease to 0.28 1ps/ha. It was further assumed that the tube well irrigation systems would be able to operate for about 3,500 hours per year when they were provided with a dedicated power supply. Thus, a 150 m3h-1 water point serving a CCA of 100 ha would be able to provide 525 mm per annum to this area. A public tube well would provide water to irrigate 34.5 ha in rabi and 56.5 ha in kharif in a command area of 100 ha.

A typical public tube well system consists of a well, submersible electrical pump and a brick-built pump house. From the well, water is pumped into a tank or so called elevated distribution chamber, from where it flows in a buried PVC pipe distribution system, which has the form of two closed loops each serving about 50 ha. On the pipe systems alfalfa outlet valves are constructed each serving about 5 ha and operated by farmers. Every tube well system has around 20 outlets. The length of the field tube well channels remains limited to 150 m. Public tube wells are grouped together in a cluster of some 20 to 30 wells. One cluster has one independent electrical feeder line, which connects all wells to one sub-station. The operation of the system was envisaged as follows. The two or more loops would in principle be supplied simultaneously. Within a loop, the command area of about 50 ha was divided into seven sub-commands of about 7 ha each, which were called area-daycommands. The idea was that such area would get the total water supply (75 m3h-1) for one day, the other 6 ha areas not getting water on that day. Farmers within each area-day command would form a committee and elect a leader. The area-day committee would organize the internal water distribution, with allocation times proportional to the holding sizes. The leader would supervise the water distribution within the area-day command area. Leaders of the area-day committees would elect five representatives to form a Tube well Management Committee (TMC) for each tube well. The TMC would be responsible for coordination and cooperation among area-day committees, for solving disputes and for advising the concerned Junior Engineers of the Department of Irrigation (DoI) in working out a rotational water allocation schedule. The President of each tube well committee would represent the tube well farmers on a Tube well Cluster Committee. Operation of the tube well was assigned to a tube well operator employed by the Department of Irrigation. Private tube well development was promoted by Free Boring Schemes in several states of India. In Uttar Pradesh, drilling of shallow tube wells was subsidized for farm holdings smaller than 2 ha. Investments by farmers were made in the pump and motor.

26.3 State Tube well (STW) programs

A major instrument of public policy – State Tube well (STW) programs – is devised originally to stimulate groundwater irrigation and to ensure that the access to this communal resource is diffused and is not monopolised by the rural elite. For hard rock regions, open dug wells are technically found to be ideally suited. Average command area of dug wells being rather low (less than 2 hectare), it would mean, in operational terms, government coping with an innumerable number of open dug wells. The other major problem with public tube well programs is their management, efficiency and quality of irrigation service they are able to provide. Numerous field studies, have pointed out poor maintenance, lack of accountability of the tube well operator of the community, domination by local elite, frequent power cuts, delays in repair and procurement of spare-parts, local feuds regarding the right of passage, etc., are amongst the several problems that STW programs suffer from. It was found that small farmers did benefit from public tube wells through improvement in crop pattern, crop yields, and cropping intensity. However, overall experience with public tube wells in various regions of the country is quite disappointing from the point of efficiency. As far as equitable distribution is concerned, the rural elite usually succeed in appropriating most of the benefits of public supply.

26.4 Community management

An important alternative to state intervention is that of community management. Democratic village institutions can play the crucial role of allocating groundwater through community decisions, if properly re-vitalised. This approach aims to enable the village community to make use of the information and control it possesses on local resources in order to prevent depletion. If farmers feel a genuine sense of ‘participation’ in community decisions, they may be much more inclined to comply with them than with state-enforced regulations.

26.4.1 Community Wells: an example

The disillusionment experienced with the working and performance of public tube wells with regard to both efficiency and equity concerns has led to the search for alternative institutional arrangements for groundwater management. Based on the theoretical premise that involving beneficiaries in the management of groundwater would help to solve problems which public tube wells suffer, certain forms of institutional arrangements like community wells and cooperatives could be advocated in the country. The functioning and management of these forms usually exhibit a mix of both successes and failures, as documented by several empirical investigations. Crucial factors for ‘success’ of such arrangements (as identified from literature) are the small size of the groups and homogeneity in the group members in terms of caste and landholding, quality of leadership, external support in both leadership, and management. Community processes may succeed to instill a sense of responsibility for the conservation of a community resource, such as groundwater. This requires a fundamental change in the perceived ownership rights, which in turn makes the approach problematic to implement. It is also important to note that the success of community management largely depends on the cooperation amongst the stakeholders. Their cooperation might arise in two ways. First, if there is a collective gain from the conservation of the resource that is larger than the individual private gains. This condition is, however, unlikely to be fulfilled in case of large farmers, who therefore, tend not to cooperate. Second, the problem of ‘free-riders’ can be sought through coercion and sanctions (e.g., imposition of fines on those who violate the agreed rules of water use). Unfortunately, in rural India, it is the case that rich large farmers are precisely in that position, who also stand to gain from the exploitation of groundwater.

26.5 Property rights

There is a lack of properly specified property rights on groundwater resources in India. In fact, it is extremely difficult to define property rights to groundwater. Customarily, in India, the rights in groundwater belong to the landowner as groundwater is attached to the land property. There is no limitation on the volume of groundwater extraction by a landowner. Since, landownership is a prerequisite to ownership of groundwater, it is difficult to assign ‘open access’ nature to groundwater resource. Although land owners own groundwater, this right is limited by the huge investment necessary to tap the groundwater by construction / drilling of irrigation well(s) and high well failure probability, which makes a selected few among them to have access to groundwater. Unless groundwater is tapped in a well and water is available in it, there is no accessibility, since there is no guarantee that any land owner who attempts to construct / drill a well is assured of groundwater, even for a short period. Therefore, there is need for a legislative change in India by limiting groundwater extraction over a particular period to the amount of water that percolates through the land over the same time period or by defining some kind of collective property rights over groundwater. However, it is rather difficult though not completely dismissible, to define and legally enforce such property rights. Also, some fundamental changes with regard to redefining property rights structure are required which should exhibit certain extent of flexibility and dynamism so as to appropriately address the varied nature of groundwater related issues in the country.

 Social ownership of wells – a ‘mixed’ intervention Socialising wells even if motors continue to be privately owned is another form of intervention to control groundwater overexploitation. Such socialization of wells has major advantages like,

1) prevention of overexploitation since public control could be exercised on the number and depth of wells in a particular area;

2) reducing problem of well interference by facilitating rational location of wells through coordinated planning;

3) equitable distribution of groundwater as large farmers would not have virtual monopoly of access to this resource;

4) transferring the risks in drilling wells from private individuals to community or government;

5) facilitate emergence of community management. Nevertheless, it has been largely overlooked in the literature on the management of groundwater resource