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 canals 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 of10 to 20 cm per kilometre still baffles experts today for its minute precision.
Built during the regime of King Dathusena in fifth century AD, who also sponsored the construction of Kala Wawa reservoir, Yoda ela was constructed to convey excess water from Kala Wawa in Polonnaruwa to Thissa Wawa reservoir in Anuradhapura.
However the ancient engineering methods in calculating the exact elevation of the Kala Wewa against ThissaWawa 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 Wawa to Thissa Wawa. The canal was not designed for the quick conveying of water from Kala Wawa to Thissa Wawa but to create mass of water between the two reservoirs, which would in turn provided for agriculture and the use of humans and animals.
Another unique feature of the 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 a features had been added to the canal since its construction. King Parakramabahu who governed the country nearly 700 years after the Yoda Wawa, reconstructed the canal added more feeders to the canal starting from thirty four reservoirs found between Kala Wawa and Thissa Wawa, re-naming it Jaya Ganga or the river of victory.
The extra water from these tanks would be fed to the canal which would distribute it in an area of 180 square miles feeding 11,400 acres of paddy lands and 120 small tanks.
However part of this ingenious creation was destroyed during the attempts to create a second Jaya Ganga under the Mahaweli Development Project causing dearth of water to some parts of the dry zone while measures are now been taken to reverse the damage done to an engineering marvel of ancient Sri Lanka.