The First Oblique Dam in the world
The Tissa Wewa is one of the four large ancient irrigation tanks in the area and is believed to be constructed the 3rd Century BC by King Yatala Tissa, or regional king Maha Naga who is a brother of king Devanampiyatissa (250-210 BC).
Since the rainfall of this area is low and the catchment area is small, the builder of the tank took all these in to consideration in building the bund (embankment). The water was retained at about 13 feet depth and left only 5 feet between the water level and the top of the bank. The embankment is about 1.2 km long. A single flood escape section (pita wana) about 100 meters in length is located on the eastern side. From this the water is flown to Yodha Wewa down stream. The surface area of the tank covered 652 acres resulting a capacity of 160 million cubic feet. According to a report written in 1858 by Mr. G. D, B. Harrison, the bund was was built of large roughly-hewn blocks of stone, few of which are less than a ton in weight.
During the restoration work in 1871, the top of the banks was cut down by 3 feet since much of it was worn away. Water was retained to a level of 10 feet. Just about 25 years later it was realised that this was not the optimum and it was rebuilt to the original specifications set by of the Sri Lankan irrigation engineers over 2300 years ago.
Tissa Wewa is also an engineering marvel of the Sri Lanka’s ancient tank building technology, for the dam built across Kirindi Oya to divert water to Tissa Wewa is the first known oblique dam in the world which proves the level of knowledge the Sri Lankan Engineers had on handling large bodies of water. The Europeans understood the principles and concepts of the oblique dams only in the 18th Centaury – 2100 years later.
Henry Parker, in his book ‘Ancient Ceylon’ published in 1909 describes this marvel
“…. The special point of interest in the Kirindi-oya dam is the astonishing fact that instead of being taken across the river by the shortest possible line, as one would expect, it was built at an oblique angle, which, from the traces I saw, I judged to be nearly forty-five degrees from the direct line. There is a possibility that this does not prove that the principle of the oblique dam, and of its greater discharging power than one built square across a river, the knowledge of which was only acquired in comparatively recent years in Europe was understood in Ceylon in very early times. Mr. Harrison, in commenting on this oblique dam, stated that in India there was an idea that one built at such an angle would be less exposed to the action of the current than one built square across the river. The Sinhalese possessed profound practical knowledge of the best methods of dealing with water, and the illustrations in Fig. No. 133, of typical dams 40 feet wide, the usual size of the larger ancient works, show clearly that they believed that such a dam must have much greater stability than one of the same width built square across a river; and especially must be more capable of withstanding violent shocks due to the impact of great tree trunks, than the dam. It is evident that in the oblique dam the blow of a log carried by the water would have much less tendency to displace a stone than in the other. Nevertheless nearly all the later dams were built square across the rivers, probably because that was the line of the rocks, on which they were founded. …. “
Today, water from the Tissa Wewa and the other tanks is used to irrigate the paddy fields near Tissa keeping the surroundings lush and green year round. Especially at dawn and sunset, the Tissa Wewa, part of the Wirawila Bird Sanctuary is a great place to see a variety of water-bird life.
- Ancient Irrigation Tanks of Sri Lanka
- Ancient Heritage Sites of Sri Lanka
- Other Places of Interest Within close proximity
Map of Tissamaharama Tissa Wewa
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Travel Directions to Tissamaharama Tissa Wewa
Route from Colombo to Tissamaharama Tissa Wewa
|Through : Ratnapura – Kahawatta – Thanamalwila|
Distance : 225 km
Travel time : 5 hours
Driving directions : see on google map