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History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c32.s2.t2: Reservoirs

History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c32.s2.t2

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Reservoirs

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Reservoirs are constructed to impound water to irrigate large tracts of arable land in the absence of rivers and dependable channels leading off from them. Usually a reservoir is surrounded on three sides by earthern embankments and the fourth side is open to the catchment area from which water flows down to collect in the basin of the reservoir. The water reaches the fields by gravity flow, below the embankments through openings or sluice gates or valves. The reservoirs which are fed by channels from rivers are known as “system tanks”. These types of reservoirs were constructed mostly in the southern region to augment irrigation needs. The artificial reservoirs, usually referred to in Anglo-Indian jargon as ‘tanks’, were variously known as *śarasi* (Sanskrit), *ayam*, *eri*, *taṭāka*(Tamil), *samudra*, *sarovara* (Kannada) and so on. The reservoirs were named after the benefactors, royal dignitaries, rulers, dynasties, deities with the above mentioned names as suffixes. To indicate the variation in size and economic importance of tanks, *eri*, *samudra*, *sarovar* applied to very big water formations. Lesser formations, artificial or natural, were also designated by such names.

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Much attention was paid to the proper location of tanks and dams. The *Mahābhārata* (Roy, Eng.Tr. II, p. 14) stresses that large tanks and lakes should be constructed at proper distances. Manu, the Law giver, advocates that dams, wells, tanks and *prasarvaṇas* should be built where boundaries meet (*MS*, VIII, 248; vide also Eng.Tr by Buhler). As their locations were vulnerable to attacks by the enemies the idea of locating them on the boundary lines was not advocated by Kauṭilya. He recommends that the tanks and dams should be constructed in the centre of a province or village (*AŚ*, III, 51, Shamasastry, 1961). Tiruvalluvar in his *Tirukkuṛal*; ‘Sacred Couplets’ (22.5; vide Eng.tr. Pope, 1886) compares wealth in the hands of the liberal minded people to the water in the Central tank and this confirms that tanks were located at the central place for all to benefit, such public tanks were known in Tamil Ūruṇi-kuḷam (drinking water pond for public).

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The site selected for the construction of large reservoirs by the tank builders was in between two mountains; for the mountain slopes on either side served as the natural embankment. This sort of arrangement undoubtedly increased the storage capacity of the reservoir. This technique is, of course, possible where there is such a natural arrangement. The famous Sudarsana lake in Kathiawar was located round the mountain Girnar. It was “so well joined in construction as to rival the spur of a mountain” (EI, VIII, No. 6, p. 46). The Ciramegha taṭāka constructed in the first quarter of the 7th century A.D. by the Pallava Mahendravarman is by far the largest tank in the Cingleput district, Tamil Nadu. It is situated in between two hills which form the natural embankment for it. “The bund rests upon the bases of two hills and lets rise here and there in the centre of the reservoir making it the prettiest tank in the district” (Madras District Manuals: North Arcot, II, p. 305). As already mentioned, the Bhojapur lake near Bhopal was created by constructing two solid masonry dams across the watershed of a circle of hills. The Rāmappa lake constructed during the reign of the Kākatīya Ganapatideva at a distance of 44 miles north-east of Warangal (Andhra Pradesh) is an excellent testimony to the skill of the Kākatīyas in irrigation works of a high order. This magnificent lake is formed by a ring of hills on three sides with a colossal bund (embankment) on the northern side (Gopal Reddy, p. 62). The same technique was applied by them in constructing a tank at Buddhapuri (Andhra Pradesh) (CTI, p. 52).

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After selecting the site either in a hilly tract or in plains, the bed of the reservoir in the basin system was strengthened with hard clay. Further, the entire area enclosed by a group of hills or earthern embankments was adjusted to form the bed of the reservoir. The elevation (kūrma) in the middle of the tank bed was totally avoided. Otherwise, the storage capacity of the reservoir would be reduced. The bed of the reservoir at the egress was formed of stony bed along a tortuous line, so that the water issued from it whirled round with great force, forming strong eddies (EI, XIV, p. 108, f.n. 8). It was provided with an inlet and outlet channels and the inlet channel was normally three yojanas distant from its source. In the basin system it was also the practice to carry the flood waters into the basin by canals. Main canals carried the water from a river. Distribution canals fed the water from the main canals into the basin. A dam across the portions of hills was constructed of a firm and compact stone wall. The stones from the quarry were straight and long to withstand pressure and strain. In the mountainous tract the question of an earthern embankment strengthening it with stone facing did not arise; whereas in the level plain it was necessary to throw up earthern banks all around the tank bund.

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Taṭākas were dug and built either in the middle or the peripheral area of the village. Care was always taken that in the site chosen there were springs of good drinkable water. A well was usually dug in the middle of the tank with its length in the north south direction. The tank was also fitted with an inlet and outlet channels for filling and emptying it (Kalavali, 2:4; Nānmaṇikkaḍigai, 73:3). Big tanks attached to temples were provided with a number of deep sunk wells (urai-kiṇaru) and maṇḍapa at the centre which was known in Tamil as nīrāli maṇḍapa. Such tanks were generally provided with flights of steps, a covered verandāh or corridors or platform all round and ornamental gateways on all the four sides (VV. p. 51).

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Although isolated tanks which were fed by the run off waters from their own catchment did exist, it was common to have tanks as part of an interconnected chain of tanks, wherein the surplus waters of one flowed down to the next tank down the line and so on. It would be of topical interest here to quote the rules laid down in the Arthaśāstra.

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“The water of the lower tank, excavated later on, shall not irrigate the field (already) irrigated from the higher tank; and the natural flow of water from a higher to a lower tank shall not be stopped, unless the lower tank has ceased to be useful for three consecutive years” (AS. II. 9). The real significance of this injunction laid down by Kauṭilya is that there was such a system of carrying the surplus water of one tank to another in ancient times. We have two classic instances from the south. The Vīranārāyaṇa eri or Viranam tank (first half of the 10th century A.D.) is at the fag end of the Kaveri delta near Kattumannar Koil (South Arcot District) and 8 miles west of Gaṅgaikoṇḍasolapuram (Tirucirappalli district). The bund of the extant reservoir alone is 10 miles in length and has amean width of some 3 miles. “The circumference of the tank when it is full is nearly 25 miles” (GAAD, 1906, p. 132). The surplus water of the famous ‘Colaganam’ tank (now in ruined condition) constructed by the Cola Rajendra I in 1012-14 A.D. at Gaṅgaikoṇḍa-solapuram went to make up this tank through a canal. Another interesting instance comes from Karnataka. A Kannada inscription (IA, VI. No. 32, pp. 138 ff.) dated 1096-97 A.D. from Kāṭṭageri (Bādāmi Taluk, Katadgi district) refers to the existence of a ‘Larger Big tank’ during the rule of the Western Calukya ruler Vikramaditya VI. J.F. Fleet, who identified the place and the tank based on the inscription, attributes three reasons for the sustained water supply in that area after in situ inspection of the place. “The system of tanks at Kāṭṭageri was formerly a large one. First, there is the small tank, on the west of the Fort, and close under the walls ... Secondly, there is a larger tank, on a slightly higher level, which if repaired, would, when full, include the proceeding in itself, formed by an embankment running to the south from just below the south-east corner of the Fort. And thirdly, about 1/4 of a mile away to the south-east of the proceeding, and on a lower level there are the remains of a large embankment, now breached and quite useless, which when in repair, evidently formed a tank of considerable area”. From the above description, it is discernible that the method of draining the surplus water from the tank at the higher level to the tank at the lower level must have been successfully applied in this case. These two instances prove that the ancients had a sound knowledge of hydraulic engineering while planning and executing the irrigation works.

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