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There were three sluices, two at about the same level being in the deeper part of the bank, and one at a slightly higher level near the middle of the southern arm. The middle one (Fig. 128), of which only I have particulars, had a rectangular bisōkoṭuwa 10 feet 5 inches long, parallel to the bank, and 6 feet 3 inches wide. There was a single rectangular stone culvert, 13 inches wide and 12 inches high in the inlet portion, and 12 inches wide and 12 inches high in the outlet part, the latter being raised 3 inches above the floor of the bisōkoṭuwa. The walls, 9 feet 5 inches high, were built of brickwork, and their lower part, for a height of 5 feet 10 inches, was lined with thin monolithic stone slabs, laid on edge.
The brickwork portion of the sluice was repaired or rebuilt several times, there being bricks of four different sizes in it. Some which were 2 inches thick belonged to the tenth or twelfth century A.D., and point to the last restoration of the work.
Others, 17 inches long and 2.33 inches thick, may have been burnt in the first or second century A.D. Those of a third type were 18.18 inches long, 9.12 inches wide, and 3.22 inches thick, Bt. being 29.3 and the contents 534 cubic inches. These belong to the period of very large bricks, extending over the second half of the second century B.C. and the early years of the first century.
The fourth type had a length of 17.75 inches, and a thickness of 2.75 inches, Bt. was 244, and if the width was half the length the contents would be 433 cubic inches. Apparently these bricks cannot belong to the same period as the last ones, and if, as is probable, they are of prior date, they may have been burnt in the third century B.C. It is possible, therefore, that the reservoir may have been constructed at that early period. The flat slopes of the bank also indicate a very early date.
Three flood-escapes were provided; one at the northern end of the bank, measuring 450 feet in width, but probably scoured out and much widened by floods; one at the southern end about 80 feet in width, these being on the natural surface of the ground; and a waste-weir of stone masonry
built in the angle at the commencement of the southern arm of the bank. Most probably this was of later date than the original formation of the reservoir. It was 270 feet long, and in its form of construction it resembled many subsequent works of the kind (Fig. 129).
In the deepest part it had five courses of wedged and partlycut stones, the top one being 27 inches deep at the outer face, and the others 18 or 20 inches; each course was set back 3 inches from the face of the course below, and was sunk an inch deep into it. The top of the weir was 17 feet wide, and it had a backing, along the side adjoining the tank, of brickwork apparently laid in mud, to prevent leakage through the stonework. At a distance of 10 feet from the outer face there was a row of dwarf cut-stone pillars, about 12 inches square and 2 feet 7 inches high, fixed in the top of the weir at irregular distances, which ranged from 10 feet to 17 feet. These were evidently placed there in order to assist in raising a temporary dam of sticks and earth after the floods had ceased, so as to retain an additional depth of perhaps 2 feet of water in the reservoir, an extremely hazardous proceeding when the level of the crest of the weir was itself dangerously near that of the top of the embankment.
The crest of the weir was 13 feet 6 inches above the sills of the low-level sluices, and the top of the bank was only 4 feet higher. At the weir level the area of the reservoir was 800 acres, and its capacity 200 million cubic feet. With an extra depth of 2 feet of water temporarily retained, the area became 918 acres, and the capacity 275 million cubic feet. The tank has recently been restored with a waterlevel about 2 feet below the original height of the weir, and an area of 646 acres, which was probably nearly the primitive size of the work.
THE SOUTHERN RESERVOIRS
During the third century B.C., King Mahā-Naga, the brother of Dēvānam-piya Tissa, and tributary king of southern Ceylon, appears to have formed a reservoir called Tissa-vapi, at his capital, Māgama. He or his immediate successors, in the
latter part of that century or the first half of the second century B.C., constructed also the Dūratissa-vāpi, 'the Far Tissa' tank, as well as another called Digha-vāpi, the Long Tank.' To these may probably be added one now termed Yōdakandiya, 'the Giant Embankment,' the original name of which is unknown.
The southern Tissa-waewa was made in a shallow valley about a mile and a half east of the Kirindi river, which flowed
past the capital. The town occupied the ground between the reservoir and the river, and for some distance lower down the valley, and also extended on the eastern side of the tank. The chief purpose of the work was the storage of water for the use of the city; it is not certain that any rice fields were irrigated by means of it, at any rate in very early times. Although the area from which water flows into the reservoir is very small, being only some five square miles, it is considerably larger than that of Abhaya-waewa, at Anuradhapura. The rainfall amounts to about 47 inches per annum. The early
designer of the work evidently gave this matter careful consideration, and decided that under such conditions it would be safe to allow a smaller margin than usual between the waterlevel and the crest of the bank; he fixed this at 5 feet, and his opinion has been justified by later experience.
The reservoir was formed by raising a straight bank about half-way across the bed of the valley until it met a low ridge with two slight elevations on it. From that point it was deflected slightly up-stream, so as to follow this ridge and save earthwork.
In the first century A.D., King Ila-Nāga (38-44 A.D.) improved the appearance of the work by abandoning the ridge, and in place of it continuing the straight portion of the bank in one line to the eastern side of the valley. The mounds on the ridge now form two small islands.
As there is no record of its restoration, the tank may have remained in working order until the end of the twelfth century, beyond which time the histories do not contain any references to Magama. At last, however, probably owing to continued neglect of the ordinary works of maintenance, it was breached; and the town, which had evidently dwindled into an unimportant settlement, was totally abandoned, the residents being too apathetic to carry out the small and simple work of repair that was necessary. The whole bed of the reservoir, the embankment, and the former rice fields or the lands on the low side of the bank, as well as the site of the old city, then became gradually overspread by a thick forest growth, infested by wild buffaloes, elephants, and bears. It is clear that the breaching of the embankment must have occurred several centuries ago.
The embankment was about three-quarters of a mile long, and after King Ila-Nāga's improvements was practically straight from end to end. It had a top which appears to have been always used as a cart-road (as at present), and was from 15 to 20 feet wide, with the flat side slopes that characterise many other early works. The inner slope was at the rate of about 5.1 feet horizontal to one foot vertical, and the outer one 4'4 feet to one. The level of the highest part of the bank was