Giant’s Tank is a marvel of ancient irrigation engineering in Sri Lanka and is a great place to see rare waders

Giant’s Tank (Yodha Vewa in Sinhalese) situated 25 km south-east of Mannar in north-western Sri Lanka is one of the largest ancient irrigation reservoirs of the Island, built by a Sinhalese king in 5th century AD by damming and diverting water from a river called Malwatu Oya via a 13 km canal.

British irrigation engineers who discovered Giant’s Tank in the 19th century failed to comprehend its design and considered an engineering failure. Sir James Emerson Tennent in 1860 wrote in his publication ” Ceylon – an account of the island physical, historical, and topographical with notices or its natural history. antiquities and productions”:

“From Anarajapoora, I returned to the west coast, following the line of the Malwatte-oya, the ancient Kadamba, which flows into the Gulf of Manaar, north of Aripo. Within a few miles of the coast our party passed, at Taikum, the immense causeway of cut granite, two hundred and fifty yards in length, and upwards of fifteen feet high, by which it was attempted to divert the waters of the river into the canal, that was designed to supply the Giants’ Tank. None of the great reservoirs of Ceylon have attracted so much attention as this stupendous work. The retaining bund of the reservoir, which is three hundred feet broad at the base, can be traced for more than fifteen miles, and, From Anarajapoora, I returned to the west coast, following the line of the Malwatte-oya, the ancient Kadamba, which flows into the Gulf of Manaar, north of Aripo. 

Within a few miles of the coast our party passed, at Taikum, the immense causeway of cut granite, two hundred and fifty yards in length, and upwards of fifteen feet high, by which it was attempted to divert the waters of the river into the canal, that was designed to supply the Giants’ Tank. None of the great reservoirs of Ceylon have attracted so much attention as this stupendous work. 
The retaining bund of the reservoir, which is three hundred feet broad at the base, can be traced for more than fifteen miles, and,as the country is level, the area which its waters were intended to cover would have been nearly equal to that of the lake of Geneva. At the present day the bed of the tank is the site of ten Populous villages, and of eight which are now deserted. Its restoration was successively an object of solicitude to the Dutch and British Governments, and surveys were ordered at various times to determine the expediency of reconstructing it. Its history has always been a subject of unsatisfied inquiry, as the national chronicles contain no record of its founder. A recent discovery has, however, served to damp alike historical and utilitarian speculations; for it has been ascertained that, owing to an error in the original levels, the canal from the river, instead of feeding the tank, returned its unavailing waters to the channel of the Malwatte river. Hence the costly embankment was an utter waste of labour, and the Singhalese historians, disheartened by the failure of the attempt, appeared to have made no record of the persons or the period at which the abortive enterprise was undertaken.”

Dr. Ananda W.P. Guruge in “The Waterlords Of Ancient Sri Lanka” ( UNESCO Courier , Jan, 1985 ) describes this failure of modern engineers to comprehend the ancient wisdom in Sri Lanka:

“Many a modern engineer has been baffled by the sophisticated designs on which these reservoirs and channel systems were constructed. It is known that the Dutch engineers of the eighteenth century and their British counterparts in the nineteenth failed to understand the design of the Giant Tank near Mannar on the northwestern coast. Only in recent years, when the tank was restored in conformity with the original design, was it found that leveling by the unknown engineer of the past was vastly superior to that attempted by modern engineers.”

The tank was restored between 1880 and 1902. The embankment of the tank is over 7 km in length with a height of 14 feet. Its catchment area is 38 square miles and is capable of holding 39 million cubic meters of water, feeding 162 smaller tanks (reservoirs) downstream and irrigating about 11,000 hectares of rice fields.

Today, Giant’s Tank is also a prime birding site. The tank and part of the adjacent forest which is 4,330 hectares in extent is protected as a Sanctuary. Observing birds here is mostly from the bund which is by the road, or by boat. There is no suitable accommodation near the tank. Birds to look for are Openbill, Common Coot, Pheasant-tailed Jacana, Cotton Teal, Rufous-rumped Shrike, Black Drongo, Collared Dove, Pintail, Gargany, Kestrel, Great Cormorant, Striated Weaver, Baya Weaver, Spot-billed Pelican and Purple Coot.

Grey Heron

Cormorants

Asian Openbill

Glossy Ibis

Pheasant-tailed Jacana

Purple Swamp Hen

(All photographs except Google maps are by the author. The visit to Adam’s Bridge was arranged by Flamingo Tours)