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in the face adjoining the water, and 2 feet to one in the outer face. The up-stream face was not protected as usual by a layer of small boulders. The total height was about 30 feet. The top was considerably worn down, so that the original level of the flood-escape was uncertain; if, as is probable, it was 13 feet below the crest, the area of the reservoir was 470 acres, and its capacity 141 million cubic feet. As now restored, the tank covers 635 acres.
The sluices were completely destroyed before the modern restoration. Apparently only the upper eight or ten feet of water were drawn off for irrigating or other purposes. A tradition, to which the inscription of Kalyānavati appears to contain a reference, states that the reservoir once possessed seven sluices; it seems to have been without any foundation in fact. It is unlikely that there were more than two, one of them being near the southern end.
Floods calculated at 4000 cubic feet per second are expected to be received by the reservoir from a catchment area of only ten square miles, in which the mean rainfall is about 78 inches. The ancient designer of the works, who may have had experience of floods in much drier districts only, must have greatly under-estimated them; and totally inadequate space was left for their escape. The breaching of the embankment on several occasions must have been the result. Bricks of four sizes in the southern sluice show that it had been rebuilt three times, and there were three breaches in the bank at the time of the last restoration, as well as in the thirteenth century. These prove that the floods found their way over the crest of the bank on both occasions.
It is probably to the early part of the first century B.C. that the construction of Nuwara-waewa, 'The City Tank,' the last of the early reservoirs of Anuradhapura, must be assigned. It is on the east side of the Kadamba river or Malwatta-oya, and a mile and a half distant from the present town, in a shallow flat valley, with a drainage area of about 29 square miles, from which no excessive floods were to be expected, the rain
fall amounting to only 55 inches per annum. was utilised partly for irrigating rice fields and partly for supplying water to adjoining monasteries and suburbs.
The embankment follows the example of that at Tissawaewa, Anuradhapura, that is, the higher portion, a mile long, crosses the bed of the valley, while at each side long arms stretch up-stream at obtuse angles, to sufficiently elevated ground to prevent the escape of floods round their ends. At the southern end of the main bank a long mound of high ground rendered any earth-filling unnecessary for three-quarters of a mile; the southern arm began on the opposite side of this. The total length was three miles. The embankment was 37 feet high in the bed of the valley, above the sill of the low-level sluice, and from 12 to 16 feet wide on the top. The side facing the water sloped downward at the rate of 3 feet horizontal to one foot vertical, to the top of the wedged stonework or 'pitching' that protected the face from erosion; this began at about 4 feet below the crest of the bank, and was laid at a much steeper inclination, perhaps 1 or 2 to one. The outer face sloped at about 24 feet horizontal to one foot vertical. The main bank appears never to have given way excepting at one insignificant breach, which may have been cut, but there is some leakage through the soil under it.
This reservoir was provided with two sluices, one being at a low level, and the other having a sill 3 feet 1 inch higher. At the low-level sluice, the bisōkoṭuwa measured 11 feet in the line of the culvert, and 15 feet in a transverse direction; it had walls 3 feet 6 inches thick, which rose 14 feet above the sill. It was lined with stone slabs.
There were two inlet and two outlet culverts built of stone. The former were only 17 feet 6 inches long, and were separated by a masonry wall 6 feet 6 inches thick; they were 2 feet wide, and 4 feet 2 inches high. An open paved inlet channel, 71 feet 6 inches long and 15 feet wide, led up to them; this had side walls 3 feet 6 inches thick.
The outlet culverts were about 156 feet long, and were separated by a wall 7 feet thick. They rested on a floor 18
inches thick. Each culvert was 2 feet wide and 2 feet 9 inches high; their outer walls were 18 inches thick, and they were covered with large stone slabs.
The bisōkotuwa of the high-level sluice was built of brick and not lined with stone; it measured 8 feet 4 inches transversely, and 7 feet 10 inches in the line of the culverts. It was 22 feet high, and had walls 3 feet thick.
136 Plan and Section of Nuwara-waewa Low-level Sluice
137. Plan and Section of Nuwara-waewa High-level Sluice
FIGS. 136-139. Nuwara-waewa Sluices, and Anuradhapura Banks.
The inlet culvert was of a peculiar form. It began inside the reservoir, at 115 feet from the toe of the bank, as a single rectangular stone culvert, 2 feet 9 inches high and 2 feet 6 inches wide, with walls and floor 18 inches thick, and cover-stones one foot thick. At 148 feet from its entrance it was converted into two culverts, 2 feet wide and 3 feet high, with the wall between them, the side walls, and floor 2 feet thick, and cover-stones 18
inches thick. These were 25 feet long up to the interior of the bisōkotuwa.
There were two outlet culverts, 14 inches wide and 20 inches high, separated by a wall 2 feet 8 inches thick, having sidewalls and cover-stones 18 inches thick, and a floor 2 feet thick. They were 154 feet long, and the total length from the entrance of the sluice to the outlet was 335 feet. A thickness of 2 feet of clay puddle was laid round all the masonry. For these particulars I am indebted to drawings of the sluices made by Mr. W. Wrightson, C.M.G., who carried out their restoration.
The bricks used in this sluice afford the only means of fixing the age of the reservoir. I was unable to measure their length; the breadth is 9.85 inches, and the thickness 3.15 inches, Bt. being 31 square inches. If the length was six times the thickness it would be 18.90 inches, making the contents 586 cubic inches. When these dimensions are compared with those of the bricks laid in the Abhaya-giri dagaba, they are seen to agree extremely closely with them. At the latter structure the length of the bricks is 18.92 inches, the breadth 9.62 inches, and the thickness 3.20 inches; Bt. is 30.7 inches, and the contents becomes 583 cubic inches. I conclude, therefore, that the reservoir was made during the reign of WaṭṭaGāmiņi, in the first twenty years of the first century B.C., or at very nearly that time.
It was repaired at subsequent times. One of these is indicated by bricks which measure 8.48 inches in breadth and 2.64 inches in thickness, to have been about 300 A.D. At a later restoration the bricks were 7.50 inches wide and 2.30 inches thick, a size which points to about the fifth century.
A flood-escape was provided in the high ground to the south of the main bank, at a rocky site. It was 136 feet wide. The sides of the cutting were protected by dry stone walling, probably at a later date than the formation of the reservoir. The permanent depth of water retained appears to have been 17 feet; but it seems probable, as the crest of the embankment was 20 feet higher, that a temporary dam of sticks and earth was raised at the site, so as to hold up a considerably greater depth of water. The top of the stone pitching which protected
the slope of the bank is 14 or 15 feet higher than the rock at the flood-escape, a height that would be unnecessary if an additional depth of water had not been retained. Had this not been the case the southern arm of the bank would also not have been required.
With a depth of 17 feet the area was 2160 acres; at six feet higher, the level now adopted, which appears to have been nearly the former higher level, it became 3180 acres, according to my tracing of the contours. The capacity then was about 1500 million cubic feet.
Immediately after the reservoir was made the flow off the catchment area must have failed to fill it year after year, and an additional supply of water was discovered to be necessary. This was obtained by taking levels-(as we may assume)up the adjoining Malwatta-oya, until a point was reached sufficiently high to permit water to be diverted from it into the reservoir. Above this spot a ridge of rocky ground approached close to the river, and indicated the most suitable place for the dam which was required. At this site, therefore, a strong masonry dam (Fig. 140) of wedged and more or less cut stones was built across the river.
Nearly all the stones were removed in 1873, for use in a roadbridge that was erected over the river. The remains show that the dam was at least 33 feet wide and nearly 160 feet long; it was well and solidly built. It rose about 8 feet high above the bed of the river. At the north end, an abutment 10 feet high, of rough stones, laid in four courses, protected the end of the bank of the channel that was cut for conveying the water to Nuwara-waewa.
From this point a channel about 40 feet wide, capable of passing a depth of four feet of water, was opened till it met with a small stream that flowed into the reservoir, at 5 miles from the dam. The bed of the channel had a gradient of about one foot in 5000 feet, a slope adopted in several later instances.
At 150 feet from the dam, an escape for floods was provided at a rocky site, in order to pass out surplus water when it entered the channel. This was 44 feet wide, and over