Ancient Sri Lankans are celebrated for their indigenous knowledge in irrigation.
Irrigation systems of ancient Sri Lanka consist of a large number of village tanks, gigantic reservoirs and an intrinsic network of water cannals connecting these tanks while supplying water to farming land.
Despite the abundance of irrigation constructions in Sri Lanka, Yoda Ela or Jaya Ganga, an 87 km long water canal carrying excess water from Kala Wewa in Polonnaruwa to ThissaWewa in Anuradhapura, is a construction dependent on remarkable instrumentation precision. Its gradient of 10 to 20cm per kilometer still baffles experts today for its minute precision.
Though it was built during the regime of King Dathusena in fifth century AD, The ancient engineering methods in calculating the exact elevation of the Kala Wewa against Thissa Wewe and the exact gradient of the canal to such fine precision had been lost with the fall of the civilisation.
Moreover the ingenuity of ancient engineers is also exhibited in how Yoda Ela was designed as an elongated reservoir, which passes through traps creating sixty six mini-catchments as it flows from Kala Wewe to Thissa Wewe. The canal was not designed for the quick conveying of water from Kala Wewe to Thissa Wewe but to create mass of water between the two reservoirs, which would in turn provided for agriculture, the use of humans and animals.
Another unique feature of Yoda Ela is that the canal has only one bund to manage the canal pressure with the influx of water. Two bunds would have increased the pressure causing damage while with one bund the water spreads on the upper side and releases the pressure creating no danger to the bund. Built along the contours the canal collects and dispenses water throughout its 87 km flow length.
Many features had been added to the canal since its construction. King Parakramabahu who governed the country nearly 700 years after the Yoda Wewe, reconstructed the canal and added more feeders to it starting from thirty four reservoirs found between Kala Wewe and Thissa Wewe, re-naming it Jaya Ganga or the river of victory.