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Over the period from 1885 to 1978 there have been major changes in the irrigation systems of the villages, during which three different types of irrigation, canal, tank and well, have been used.

4,3*1 Canal

As described in Chapter 2, the lands of Village A overlap the area under the Periyar Scheme, a major traditional canal network. Water is diverted from the River Suruli, which

distributes water to Kambam Valley, via a distribution channel (see Fig 4.1) and to individual fields via smaller distribution channels. Water is made available constantly, though at varying rates of discharge over an eight to nine month period from

June to March. Water is bunded into level fields on the eastern side of the channel for paddy cultivation. There has been no change in the methods used within this system since the inception of the Periyar Scheme in 1895- The First Settlement Register of 1885, however, shows that while there was sufficient water for a second crop in the southern section of the canal irrigated land, the northern section comprising 21% of this land received canal irrigation for only one crop. Canal water is government owned, and the sluice-gates of the distribution channel to the village are controlled by Public Works

Department officials. Farmers pay a relatively high land revenue for the use of this water on lands classified at

settlement as "wet", and progressively higher fines for the continued illegal use of canal water on lands classified as

"dry" or on occupied government land.

Ganal water has in some cases been diverted from the distribution channel to government-owned lands, having been drawn off from the channel by underground pipes into wells acting as reservoirs for water which is subsequently pumped overland to gardens in the west of the village.

The presence of the distribution channel, too, keeps the water-table to the west of the channel at an artificially high level for a large part of the year, a factor which has been important to gardenland cultivation, especially with the increased output associated with powersets.

An important part of the canal irrigation system has been the Karuvelan Tank, which is now filled in and use^L directly for agriculture# Its purpose was to act as a reservoir for canal 1 water received through the distribution channel in order to ensure a sufficient supply of water for wetland in the northern section of the village, especially during the second crop. It was also the village pool, and acted too as a barrier to

erosion, collecting the runoff from gullies flowing from west to east through the village. The encroachment of the tank took place over a period of about two to three years from 1969.

4.3.2 Tank

Tank irrigation has been used in both villages, although 1 1 6 .5 0 of its 24.33 acres are under agricultural land.

in a secondary role in conjunction with both well and canal irrigation. In Village B there are four tanks which trap the runoff of rainwater flowing from west to east through the village (Fig 4.2). Thus the level of water in the tank varies annually and seasonally with rainfall. The tanks do not

exist primarily for the purpose of directly irrigating land, their role being mainly to act as reservoirs of water, helping to maintain water levels in wells located on their eastern perimeters* This function is well appreciated by villagers in Village B, who have an as yet uninitiated scheme to build a dam in the South-West of the village to trap runoff flowing from south-west to north-east through the village (see Fig 4.2).

Qne?of the tanks (T4), has been used directly as a source of

. . 1

irrigation in the past, irrigating a limited area of land , which was at the same time under well irrigation, through a

small outlet channel for three to four months annually, sufficient for a single crop of paddy. However this is now dry. Another of the tanks (T2), was classified as a second class source of irrigation in the 1885 settlement register, irrigating some 2.64 acres of land. It has not performed this function, however, within living memory#

The tanks, as well as acting as reservoirs for irrigation

water, have been important in surface erosion. rwt\(

(the four tanks in Village B form a chain in a section of the drainage network). Tanks also perform the function of acting as the village pond (T3 is the most important in this respect), 1 Reports suggest this varied between 7.26 and 25*71 acres,

implying that it was a minor irrigation source depending very much on rainfall for its effect, and probably supplemented by well irrigation.

which is of importance to the life of the village, as v/ell

as offering the important facility for washing cattle. The tank in Village A, as described above, has ceased to exist, but the river may perform many of the functions of the tank. While tank levels have declined in Village B, so has the demand for their use, with declining numbers of draft cattle.

4.3.3 Well

Wells are independently controlled sources of irrigation built to act as reservoirs of ground water as well as points of access to groundwater. They are generally of a width and breadth of about 25 feet by 25 feet. The depth of operating wells must reach below the level of the water table during the rainy season, and its supply of water depends upon the length of time during the year during which the base of the well remains below the groundwater level. Water flows into the well through underground aquifers which are tapped either by the well itself or by boreholes added to the well.

The extent of well irrigation in either village depends, therefore, on the spatial extent of access to groundwater.

There are some local variations within the village in the hardness of the parent rock , and thus the ability to sink 1

wells, and also in the courses of underground aquifers because of geological structure. However, the main determinant of access to groundwater is the level of the water- table, which varies positively with seasonal rainfall, and negatively with altitude.

1 This constraint on powerset adoption is noted for North Arcot District, Tamilnadu by B. H a m s s (1977)*

Idealised water table levels for wet and dry seasons are shown for both villages in Fig 4.6. The spatial extent of well-irrigated land is clearly defined in both villages; wells have been sunk outside areas of possible access to groundwater, and are thus physical proof of unsuccessful ventures, and help to mark the boundary of possible access.

The direct seasonal relationship between groundwater availability, as measured in well water levels, and rainfall has been demonstrated by C.M. Bandara (1974) for North Arcot District, which has a largely similar rainfall regime and geological structure. Unfortunately it was not possible to collect data from within the village on changing seasonal groundwater levels, or for the Kambam Valley .1

Since 1885 there have been two major methods of drawing water from wells. Until the introduction of powersets in Village A in 1967 and in Village B in 1963* the traditional method of drawing water was the kamalai, a bullock operated machine. (The ettram, an ancient method of drawing water by a lever system, was in operation in one well in Village A from 1915 to 1925)» Some wells had the facility to operate more than one kamalai at a time. The kamalai is only able to operate up to a maximum depth of about 50 feet, as increasing depth from which water is draini necessitates increasing effort over increasing time for diminishing output.

1 The Groundwater Directorate, Madras, have been collecting data