« PreviousContinue »
The embankment of Tissa-waewa is 11,000 feet, or 21 miles, in length, and about 25 feet high across the bed of the valley, which is flat for a long distance. The width of the crest averages 12 feet, but in parts is 18 feet. The outer side slopes at the rate of 3 feet horizontal to I foot vertical; the upper part of the inner slope, adjoining the water, falls at the rate of 2.8 feet horizontal to I foot vertical until at the level of the flood escape it reaches the stone facing of boulders and wedged stones which is laid to protect it from erosion by waves; this is at an inclination of 1 feet horizontal to I foot vertical (Fig. 139). The bank is a well made and substantial work, which with a little attention may last practically for ever; it appears to be in its original state, and is a credit to the men who raised it. There is no sign that it has ever given way except at the low-level sluice, where there was a small breach when I first saw the work in 1873.
A low-level sluice was built in the northern arm of the embankment, and a high-level one at about the middle of the southern arm. These had the usual rectangular wells and stone culverts. The well at the low-level sluice was nine feet wide in the line of the culvert.
A place for the escape of floods was left at each end of the bank, unprotected by masonry. The level at both was about 15 feet 4 inches above the sill of the low-level sluice; it is now raised to 17 feet 6 inches. Their total width only amounted to about 50 feet, the catchment basin of this tank being a very small one.
The area of Tissa-waewa was about 396 acres; as now enlarged it may be 550 acres. Its capacity is unknown.
The construction of Vavunik-kulam, a reservoir in the Northern Province, should probably be assigned to nearly the same period. Its original name was Pēli-vāpi, so-called because it was formed by raising a long embankment across the valley of a stream now termed the Pāli river. The single reference to it in the Mahāvansa (i, p. 107) shows that it was in existence before the time of Duṭṭha-Gāmiņi, and this may
carry its construction back to the third century B.C., as the Tamil ruler Elāra, who was killed by that king, and who is stated to have been on the throne for forty-four years, from 205 B.C., to 161 B.C., is not known to have made any reservoirs. Of course there remains a possibility that it was formed during the reign of Elāra, and that the early annalists omitted to record the fact.
The reference to it in the history is as follows: To the northward of the capital, at the distance of seven yōjanas, in the sand-banks of the stream flowing into the tank of Pēli vāpi gāma, four superb gems, in size about a small grindstone1 and of the colour of the Umma flower, were produced.' The name, the distance from the city, and the reference to a stream with sand-banks render the identification certain, there being no other reservoir on the river, and no other stream with sandbanks at that distance north of Anuradhapura.
According to my hand copy of the inscription left by King Wasabha (66-110 A.D.) at Peramiyan-kulam, on the northern side of Anuradhapura-(No. 7 of Dr. E. Müller's Ancient Inscriptions)—it appears to have been granted by that king to the Community of Monks. The words in my copy are, Pali nakaraka wawiya ma tera Majibaka dini. He gave the Palināgara tank to the great thera Majjhima.' In the forest near the northern end of the embankment, Mr. C. F. S. Baker, the engineer who surveyed the tank, met with some ruins which may indicate the site of this ancient city, Pāli nāgara.
Detailed surveys have shown that when the reservoir was full the water covered an extent of 1975 acres, and the tank then had a capacity of 596 million cubic feet.
The work was of a different class from those already described, its object being solely the storage of water for the irrigation of the rich lands lower down the valley. Thus it may have been the first large reservoir entirely devoted to such a purpose. The fact that some of the most productive land in northern Ceylon would be irrigable by means of it, accounts
I do not know what is meant by this, the grindstone not being an Eastern article.
for the selection of this valley as the site of one of the first large irrigation schemes.
But the provision of water for this purpose would be useless were there not cultivators ready and willing to utilise it; it follows, therefore, that an adequate population who understood rice-growing was already established in this part of the island at this early period. We may safely assume that all could not be the descendants of settlers from the valley of the Ganges; and if not, the others must have been Dravidians, that is, most probably Nāgas, the Vaeddas being a race who were unacquainted with rice cultivation. The raising of such an embankment as that of Vavunik-kuļam would necessitate the presence of many hundreds of labourers accustomed to earthwork; the amount of work done itself indicates that there was already a large resident population in the district.
We may feel confident that other irrigation reservoirs of considerable size had been formed before the benefits derivable from large schemes of this nature had become sufficiently well known to induce the sovereign, who of course was the moving spirit in such matters, to undertake the construction of the long embankment of this tank solely for the furtherance of agriculture in an outlying part of his dominions.
The design of the work was of a simple character. A straight embankment was carried across the Pāli river, from the northern side of the valley, in a south-south-eastern direction, for a mile and a half. After arriving close to the southern side it was deflected into a south-western line for three-quarters of a mile, so as to include in the reservoir another subsidiary shallow valley, this part of the work being doubtless a subsequent addition to the original scheme. The extended bank ended by being turned round again into a south-eastern curve until it encountered higher ground. The total length is 13,350 feet, or about 2 miles.
Although the river rises only twenty miles away, and the catchment area has a rainfall which amounts to less than 50 inches per annum, the embankment has been badly breached in five places, and the reservoir has been abandoned for many
centuries, and its bed is now overgrown with jungle. There are also unmistakable signs of former breaches that have been repaired.
The only possible natural way in which five breaches can
be caused at the same time in an embankment of a reservoir is by the rising of the water until it flows over the top of the bank at any points where the earthwork is a trifle lower than elsewhere. This is what must have occurred at Vavunik
kulam; but it does not indicate, as might appear to be the case, that the space provided for the free escape of all ordinary floods was insufficient. On the contrary it may have been enough, under ordinary conditions, for a reservoir in such a site. In the northern part of the bank a flood-escape at least 80 feet wide, and possibly much more, was left open. At the southern end a width of 450 feet was allowed at the end of the extended bank, and therefore most probably a wide floodescape existed at the end of the original bank.
The experience of the last twelve years has shown that it may be suggested with confidence that the bursting of the reservoir was due to one of those violent cyclonic rainstorms which sometimes occur in this Province, and against which in most cases it is impossible to make provision, even if it could be foreseen. On the occasion of such a downfall in another part of the Northern Province in December, 1897, the actual depth of rain which fell in 24 hours, as recorded by three observers at Nedunkēni, one being the Medical Officer of the station and another his dispenser, was 31-72 inches. The enquiry which I personally made on the spot regarding the manner in which this fall was gauged satisfied me that it correctly represented the quantity of rain collected in the rain-gauge, and that in addition a small amount must have been intercepted by two high trees as the wind veered round in their direction. The storm began about three hours before this record commenced, and the total amount which fell in twenty-seven or twenty-eight hours must have been 34 or 35 inches deep.
It is almost unnecessary to state that the damage caused throughout the tract which experienced this cyclonic storm was enormous. Roads were washed away, and one iron bridge presented a curious spectacle, standing isolated over the river that it spanned, with the approaches, that is, the road on an embankment at each end of it, more or less carried away. The tanks of the district suffered most; more than 160 were burst, in all cases by the flood-water's pouring in a great volume over the crests of their banks.
One work called Periya-kulam, that had been restored by