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of the bank :-At the southern low-level sluice, 11 feet 2 inches by 8 feet 10 inches; at the central sluice, about 8 feet square; at the northern low-level sluice, 8 feet 2 inches square, and
at the northern high-level sluice, 13 feet 8
inches by 8 feet.
The culvert at the waste-weir was built of stone, and the well of the northern low-level sluice was also lined with stone, with a substantial backing of brickwork. At the others, the well of the central sluice probably, and those of the other two sluices certainly, were built of stone in the lower part,
FIG. 126. Bisōkoṭuwa. N. Low-level Sluice.
with a backing of brickwork, but after the first two or three courses were finished in brickwork only, the side of the southern low-level sluice adjoining the central line of the embankment being, however, faced throughout with stone slabs (Fig. 124). All the brickwork was laid in excellent mortar made with lime burnt from coral. The stonework in all the sluices is of the type of all later works, and consists of long thin slabs of considerable breadth, passing from one side of the wells to the other when laid in their walls. These slabs were placed on edge when used as linings of the wells, and in all sites they were fitted together with great care. The faces and beds
of the stones were well, though not finely, dressed, but the backs were left rough (see Figs. 124 and 126).
The dimensions of the bricks employed in the low-level sluices provide the only clue to the age of the reservoir. At the southern low-level sluice their length was 17.36 inches, the breadth 8.60 inches, and the thickness 2.89 inches; Bt. was 24.8 inches, and the contents 433 cubic inches. The size clearly points to some date not later than the early part of the first century B.C. The figures agree very closely with those of the Sandagiri dāgaba at Tissa, which was built by King Kakavaṇṇa-Tissa in the first half of the second century B.C., and they are also nearly those of other very early dāgabas.
The bricks in the northern low-level sluice may be of a slightly later date, as the variations in the length and breadth prove that moulds of a different size were used for them, that is, that they were not burnt at the same time as the others. They have a length of 16.70 inches, a breadth of 8-29 inches, and a thickness of 2.94 inches; Bt. is 24.4 square inches and the contents 408 cubic inches.
The thickness of the bricks at both these sluices is relatively much greater than in those of the Lankarāma dāgaba, and if that work be excluded the dimensions indicate some period either in the third century, or-if we accept the Sandagiri bricks as our guide-in the second century B.C. Considering the advanced type of the designs for the sluices, the latter is the more probable time.
The southern low-level sluice was of special interest. The unbroken state of practically all the bricks used in the face of the well, and the fact that they were all of one size, prove that this part of the work was the original structure, just as it was left by its builders. When I saw it twenty-four years ago, it was still fulfilling the purpose for which it was constructed, although the culvert was damaged; and a small
1 Mr. R. A. Powell, of the Public Works Department, the engineer who supervised the re-construction of the sluice, has informed me that in the backing' of the brickwork he found bricks of several sizes. This must indicate some subsequent repairs to that part of the work, although the lining or face of the walls appeared to be intact.
rice field was supplied with water which passed through it. It is greatly to be regretted that it was taken down and rebuilt according to an 'improved' design a few years afterwards, when the reservoir was partly restored by the Public Works Department. This is the more to be lamented for the reason that in all likelihood it was the only work of the kind of such an age in the island, unless the sluices at Vavunik-kulam are also in their original state.
As in all later sluices, the work in this one consisted of three parts, (1) a rectangular open well built near the point where the water level met the inner slope of the embankment, (2) an inlet culvert through which the water passed into this well, and (3) a discharging culvert from the well to the foot of the outer slope of the bank.
The well is called in Ceylon a bisō-koṭuwa, which literally means' Queen-enclosure,' but probably would be more correctly termed bisi-kotuwa, 'the enclosure where (the water level) lowers.' The sketch (Fig. No. 123) shows the manner in which the inner work of three of the sides was built at this sluice. The flooring was formed of long well-fitted slabs of cut stone, like those in the walls. I do not know the thickness of the brick walls; at other sluices it is often from five to six feet. Mr. Powell stated that the walls were surrounded by very good clay' puddle' for a thickness of two feet or more, and that the brickwork was of such excellent quality that he could not avoid regretting that he had been instructed to pull it down. This well was 14 feet deep; originally it was probably built up to the level of the flood escape, that is, a little more than 18 feet above the sill level.
The inlet culvert was 52 feet 6 inches long, and had a peculiar bend in its line, as shown in the plan (Fig. 122). I have seen nothing of the kind elsewhere. Across its entrance there was a block of brick masonry 7 feet thick and 9 feet long, which rose 6 feet high above the sill of the culvert and had foundations 3 feet 6 inches deep. No similar construction has been seen at other works. The culvert was rectangular, 2 feet wide and 2 feet 6 inches high at the inlet, and 2 feet 6 inches wide and 3 feet 6 inches high at its junction with the
bisōkotuwa or well. It had walls 2 feet thick, and was covered by slabs about 9 inches thick. Its floor was at the level of the bottom of the well.
The outlet or discharging culvert was of a very interesting form. For a length of 14 feet 6 inches it was divided into two culverts, each 2 feet square, separated by a wall 2 feet thick (Fig. 124). From the end of these double passages their outer walls were continued in straight lines to the outside of the embankment, gradually approaching each other until they were 2 feet 6 inches apart at the outer end. The height of the passage for the water was, however, gradually increased from 2 feet until it became 3 feet 6 inches at the end of the culvert. The walls were 2 feet thick, and on them were laid large coverstones of varying thicknesses, from about 9 inches to a foot; these were from 5 feet 9 inches to 8 feet long, or more, and like those of the floor were dressed on the face and sides. Across the outer end of this culvert there was a brick wall like that at the inlet, 6 feet high and 12 feet long. The culvert walls were built throughout of large stones, well dressed on the faces, ends, and beds, and fitted together very carefully. For all these measurements of the culverts I am indebted to the drawings of them made when the new work was about to be built.
When compared with later sluices, practically the only difference occurs in the form of the inlet. In most sluices the inlet channel is a very short one, and in large works its entrance is protected by a high wall across it, with sloping wings built at a batter, to support the soil at each side of the approach to it. The increase in the height of the discharging culvert from the well to the outlet occurs at some large works only; in most cases the section remains the same throughout. It is astonishing to find this early work adhering so closely to the best type of later designs.
No means of regulating the out-flow of the water is visible at any of the ancient sluices in Ceylon, and considerable speculation has arisen regarding the purpose for which the wells were invariably built across the line of the culverts, in the up-stream slope of the embankments. It has been
thought that the intelligent engineers who designed these great works may have believed that the culvert was relieved from internal pressure caused by the water in it, when the water was allowed to rise freely in these open wells. This opinion is easily proved to be incorrect. The bisōkotuwas, as I prefer to term the wells (the word 'well' usually implying a work with a very different function), are much larger than would be needed for such a purpose, and at the northern high-level sluice at Pāvaṭ-kulam we find a larger one than at the low-level sluices. Even when other arrangements were adopted which would really tend to relieve the culvert from excessive pressure-as by enlarging its sectional area from the well to the outlet-we still find the well always present.
As one whose duties permitted him to gain an intimate acquaintance with the ancient works, I have never concealed my admiration of the engineering knowledge of the designers of the great irrigation schemes of Ceylon, and the skill with which they constructed the works; and my friend and predecessor the late Colonel C. Woodward, R.E., expressed the same opinion to me more than thirty years ago, when recommending me to study them thoroughly. When we find, therefore, that the open well is never absent at any sluice in a reservoir, excepting only such works as the culvert under the Pāvat-kulam waste-weir, we may safely conclude that it fulfilled a very important function.
Since about the middle of last century, open wells, called ' valve-towers' when they stand clear of the embankment and 'valve-pits' when they are in it, have been built at numerous reservoirs in Europe. Their duty is to hold the valves, and the lifting-gear for working them, by means of which the outward flow of the water is regulated or totally stopped. Such also was the function of the bisōkotuwa of the Sinhalese engineers; they were the first inventors of the valve-pit, more than 2100 years ago.
It will be readily understood that in an age when ironcasting was unknown, and even the smallest plates of iron could be heated only with difficulty in the early forges, no iron or