Ancient Reservoirs and Irrigation Systems of Sri Lanka (ශ්‍රී ලංකාවේ පුරාණ වාරි කර්මාන්ත)

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Irrigation systems of ancient Sri Lanka consist of a large number of village reservoirs to gigantic reservoirs and a intrinsic network of water canals connecting these tanks while supplying water to farming land. There about 30,000 reservoirs in Sri Lanka of which the majority was built form 3rd century BC to 12th century. This compared to the Sri Lankan dry zone land area of about 40,000 sq. kilometres (where almost all the tanks are located), is almost equivalent to one reservoir for each sq. kilometer.

The first large reservoir to be built in recorded history is Abaya Wewa in 3rd century BC. From that day onward Sri Lankan tank builders developed a remarkable expertise on controlling large bodies of water which allowed them to built massive reservoirs which no other civilisation ever could have dreamt of.

The breakthrough which made the Sri Lankan Irrigation Engineers build such massive reservoirs was invention of the “Biso Kotuwa” of valve pit as early as 3rd century BC which could easily regulate the out flow extremely large water bodies. Europeans stared using the valve pits in their reservoirs only in the mid 18th century, 2100 years later according to H. Parker, an Irrigation Engineer who was in charge of restoring many ancient irrigation reservoirs in late 1800’s, in his book ‘Ancient Ceylon’

He goes on to say,

……..At first, only the simplest works of the smaller class, with very low embankments, would be undertaken; but when a better knowledge of the art of raising such banks of earth to hold back greater depths of water was acquired, schemes of a more comprehensive character would be attempted, until at last no reservoir was looked upon as too great to be constructed, and the lengths of the embankments extended for any distance up to a maximum of nine miles, while their heights in a few instances rose to more than fifty feet…………..
……… It may appear to be such a simple matter to raise a long bank of earth in order to hold back a certain quantity of rain water for bathing purposes or for watering an adjoining rice field after the rains have ceased, that any people living in hot countries where the rains are only seasonal and are followed by several almost rainless months might be expected to be struck by the idea of making these little reservoirs for themselves, without its transmission from another country ; but as a matter of fact the notion of reservoir-making appears to have been originated in only one country, and never to have been invented independently elsewhere, at any rate in the Old World. …………

Another development of the ancient irrigation systems is the remarkable instrumentation precision. When king Dathusena (459-477 AD) built Yodha Ela, also known as Jayaganga, the ancient irrigation engineers first found out that the Kala Wewa in Pollonaruwa was built on a slightly elevated ground compared to Tissa Wewa in Anuradhapura. Then he built the 54 mile ( 87 Km ) Yoda Ela with a gradient of 6-12 inches per mile ( approx 10 to 20 cm per kilometer) to carry excess water in the Kala Wewa to Tissa Wewa. How these engineers could achieve such precision still baffles experts today.