As modern pioneers of the irrigation sector in Sri Lanka, the Irrigation Department is now on the move to unveil another irrigation marvel in the country. That is the abandoned Kudavilachchiya Tank in the northeast corner of the Wilpattu National Park, about three kilometres away from the Mahavilachchiya Reservoir.
It is believed that it was constructed during the era of Prince Saliya and Ashokamala. It is known to be more than 1,900 years old. For many years, this massive irrigation asset has been hidden by the thick jungle of the Wilpattu National Park.
The tank was breached at several places when it was found. The latest surveys conducted by the Irrigation Department have identified that this massive earthen dam is 2.55km in length and the maximum height of the dam is about 32 feet – around 500,000 cubic metres of massive earthen work done by the ancient irrigation specialists.
Like other ancient reservoirs, the Kudavilachchiya Tank also consists of two sluices (bisokotuwa in ancient Sinhala terminology) which have been destroyed by treasure hunters. Luckily, the structural features of these sluices remain intact. Plenty of 8’ x 2’ x 2’ stone fillers were aligned precisely to form the sluice well and all structures were covered by two-metre to four-metre thick brick masonry to arrest leakage into the sluices. It is amazing that these nearly 2,000-year-old bricks and cement mortar also remain intact without any harm or damage. The stone-carved sluice tunnels and groves are also intact and still in working condition.
According to Anuradhapura Irrigation Engineer Lasindu Kotawilaarachchi, the two steps of the retaining wall type providing riprap protection along the entire tank bund, show the great structural knowledge used in ancient irrigation technology. However, the Irrigation Engineer emphasised that the question is, this massive earthen dam which is 2.5 kilometres long and 20-feet high has a spill length of 15m which is odd in dimension when compared to other reservoirs that hold the same capacity.
Irrigation Director Dr. Weligepola who has conducted modern hydrological studies relevant to the Kudavilachchiya Tank reveals that “though this entire bund (dam) can hold more than 46,000 acre-feet of water, the annual inflow to the reservoir might be less than 28,000 acre-feet. Therefore, this hydrological analysis proves that those ancient irrigation technicians might have some sense and knowledge of hydrological features of the upper catchment which may cope with the shorter length of the spill built at the Kudavilachchiya Tank.”
He said they have another question - why had they constructed a bigger dam wasting a massive amount of materials and human resources when the annual inflow is low? This could have been a difficult and inconvenient task those days. An interesting justification for that question can be found when walking along the Kudavilachchiya Tank bund.
“As we know in the then dry zone, the annual yield might be less than 1,750mm. But, when we consider 1,000 years or more, it can yield more water. So, that might be the reason behind the massive earthen dam. By the time they knew that the length of the spillway is not enough to cope with such an event, and so they may have introduced a breaching section artificially to the bund where geological features are not supported for a natural, safe breaching section,” he said.
“It is still can be observed that 275m away for the existing spillway, there is a stone abutment that can be considered as protecting the bund from breaching in the event of a massive flood. Even at present, the downstream protection by dress stone masonry which may be clear evidence that they have provided room for excessive water by preventing the bund from erosion. On top of this massive dress stone abutment, there are ruins of a building which can be assumed as the operation room for dam operating staff that may be a vital factor for operating the breaching section in the event of severe floods.
“Hence, these assumptions are true; this will be the first-ever evidence of the hydrological knowledge of ancient Sri Lankan irrigation technology. The Irrigation Department has now completed the relevant designs and modifications of this ancient reservoir to bring this irrigation marvel back to service our nation. Archaeological findings that have been discovered at the Kudavilachchiya Tank site which remained hidden for centuries in the Wilpattu National Park showcase the excellent irrigational engineering skills of our ancestors,” the Irrigation Engineer said.
Irrigation Engineer Kotawilaarachchi told the Daily News that they were waiting for the archaeological report on the tank to start conservation and renovation work of the totally-abandoned Kudavilachchiya Tank. He said Rs. 1,000 million would be required to complete the tank restoration project, while preserving its archaeological irrigational artifact values.
He explained further that once renovation work is over, the tank water would be solely used for the consumption of wild animals and the commencement of the Mahawilachchiya proposed water supply project, leaving water in the Mahawilachchiya Tank for cultivation purposes.
from daily news