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it a bridge 12 feet wide was constructed, supported by two pairs of wooden pillars for which socket-holes were cut in the rock. The ends of the bank at each side were protected by boulders.
At 6 miles, a bridge 154 feet long crossed the stream down which the water flowed. It was carried on three lines of stone posts, fixed in rows of three, which were 6 or 7 feet apart. Over each set of three posts a stone beam about 12 inches square and 10 feet long was placed; on these, longitudinal wooden beams must have been laid, for carrying the planking of the bridge, as shown in my restoration (Fig 141).
The bricks found at the dam are a proof of its age. They are 9-05 inches broad and 3.25 inches thick; Bt. is 309, and the length may have been 18 or 19 inches. It is evident that they belong to the period when the larger types of bricks were burnt, that is, that they must belong to the early part of the first century B.C., since they cannot be of earlier date than Nuwara-waewa.
For several centuries the water-supply provided by these works was sufficient for the requirements of the district and the people below them; but at length, as the population increased, it became insufficient in dry years. Doubtless it was observed that in flood times the greater part of the water passed over the dam in the river, and especially that when freshets occurred at times when the water was urgently needed, only a limited part of the flood could be secured.
A careful examination of the valley showed that at 31 miles below the dam in the river, two ridges projected into it, leaving a gap of only a mile between their ends. In order to increase the water-supply it was then decided to raise an embankment across the valley at this spot, closing up this gap, and impounding the floods in the reservoir thus formed, which is now termed Naccaduwa. It was a bold scheme, as floods estimated to amount to 14,000 feet per second were to be expected, and there was no suitable rock over which they could be allowed to flow; but it was carried out successfully.
The embankment, running nearly north and south, is 5550 feet long, or a little more than a mile. It was 36 feet high above the sill of the sluice, and 55 feet above the bed of the river; its top was about 20 feet wide, and both the sides sloped at the rate of 2 feet horizontal to one foot vertical. The slope facing the water was protected by a layer of small boulders.
A single sluice (Fig. 144) was built near the point where the bank crossed the river. It had the usual bisōkotuwa, IO feet 10 inches long in the line of the culverts, and 12 feet 6 inches wide. Its walls were 7 feet thick, but 11 feet thick on the side facing the tank; they were 16 feet high. The floor, and the walling for a height of 3 feet, were built of stone; above that level all the work was of brick.
Two inlet culverts, separated by a wall 2 feet thick, passed through the wall of the bisōkotuwa. They were 2 feet wide, and according to the drawings under 2 feet high. An inlet channel 9 feet wide, and 27 feet long led up to them. Its sides were protected by sloping walls of rubble stones, built at a batter.
There were two outlet culverts built of stonework, each 22 inches wide and about 18 inches high, separated by a wall 22 inches thick; they were covered by large thin slabs of stone.
In order to pass out the floods, a fine masonry dam, 44 feet wide at the crest, and 167 feet long (Fig. 145), was built at the point where the embankment abutted against the northern ridge. Its top sloped upward considerably from the back to the overfall, and the back was protected by a mass of brickwork to prevent leakage, although all the inner work of the dam consisted of boulders and wedged stones laid in good lime mortar, as well as brickwork.
In the deeper part, the work in the down-stream face consisted of seven courses of stones from one foot to 19 inches thick, each course projecting two inches beyond the one above it, which was sunk into it for about an inch. The upper course projected six inches, so as to form a coping; all the stones in it at the overfall were laid as headers,' while those at the rear face were 'stretchers.' A peculiar feature, which also occurs at some sluice inlets of stone masonry,
was a number of hammer-headed stones laid as headers in the down-stream face, so that the projecting 'head' of the hammer rested against the course above and the course below, to prevent them from moving outward (see Fig. 146).
Stone abutments were built at each end of this dam or wasteweir, with a backing of brickwork laid in lime mortar.
Part of the flood water which escaped over the dam was caught near the point where it rejoined the river, and passed down to Nuwara-waewa, by a channel about 50 feet wide. Possibly other water was permitted to flow down to this channel by a cut opened round the northern end of the waste-weir. Even by this means only limited use can have been made of the reservoir for supplying water to Nuwara-waewa, since only a shallow layer of the upper water can have been drawn off for it; and it is clear that the old channel opened from the dam in the river must have continued to be indispensable. The new tank only supplemented the old works to a small extent; part of its water was used for irrigating the land on the opposite side of the river.
The crest of the flood-escape at Nāccāduwa tank was 21 feet 6 inches below the top of the embankment, and 14 feet 2 inches above the level of the sluice. The tank had an area of 2015 acres, and a capacity of 525 million cubic feet. It is now restored so as to retain an increased depth of 8 feet 5 inches, at which the area is 3920 acres and the capacity 1600 million cubic feet.
The bricks used in the sluice measured 8.50 inches in length and 2.58 inches in thickness, Bt. being 21-8. These are the same dimensions as those of some bricks used in the repairs of the high-level sluice at Nuwara-waewa, and they show that the work at both reservoirs was done at about the same time. According to tradition, Nāccādūwa tank was made by Mahā-Sēna (277-304 A.D.); the bricks strongly support this date.
The upper part of the bisōkotuwa was built chiefly of a later type of bricks, which have a length of 12.55 inches, a breadth of 7:40 inches, and a thickness of 2.04 inches; Bt. is 15.1; and the contents 189 cubic inches. They nearly re
semble the bricks of the twelfth century found at Polannaruwa, but are not so wide; it is possible that they are of a little earlier date. There are also very large rectangular wedgeholes in some stones of the waste-weir, of a type which I have not found elsewhere excepting in twelfth century work, especially that of the time of Parakrama-Bāhu I. It is probable that he restored the work, and rebuilt the masonry weir.
When we examine the lists of reservoirs constructed by Mahā-Sēna and restored by Parakrama-Bāhu I (Mah., ii, p. 263), we see that if Nāccādūwa be included among them it must be one of two works, (1) the tank called Tissawa, Waḍunnāwa, or Vaḍdhana, or (2) Mahadāragalla. Of the rest that are found in both lists, I can identify all but the tank called Ciravāpi or Walāhassa, the first name of which, meaning 'Small Tank,' shows that it cannot be Naccaduwa. With another Tissa tank at Anuradhapura, this one is not likely to have been termed Tissawa; thus it may be Mahadāragalla.
How long the reservoir remained in order after the twelfth century is unknown. When the recent restoration was undertaken it had a deep breach at the river, and evidently it had been abandoned for many centuries. The whole bed and the embankment were overgrown with high forest, and I was informed that a year before my first visit two bear cubs were captured inside the bisōkoṭuwa; this will give an idea of the wild state into which the place had relapsed.
OTHER EARLY WORKS
It is stated in the Mahāvansa (i, p. 34) that King Kālakanni-Tissa (42-20 B.C.)' formed the great canal called Vannakaņṇa, as well as the great Amadugga tank,' but neither of these works has been identified, and the history gives no information regarding their position, nor are they again mentioned in it.
A reservoir called Paṇḍa-vāpi is referred to as being in existence during the reign of King Mahā-dāṭhika Mahā-Nāga (9-21 A.D.), and apparently it was made in pre-Christian times; but nothing is known of its construction. The name recurs