Concise Mahavamsa Ruwan Rajapakse, P.E., Sinhalanet.com 1

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Concise Mahavamsa Ruwan Rajapakse, P.E., Sinhalanet.com 24 Main purpose of Abhaya Wewa was to provide water for the city population for drinking and bathing. The embankment of Abhaya Wewa is 5,910 feet long and 22 feet high. The slope of the embankment was found to be three horizontals to one vertical. Top of the embankment has a width of six to eight feet. Slope of Abhaya Wewa was flatter than that of Panda Wewa. It could be due to the fact that later designers decided to build the embankment stronger. Reservoirs, which were built after Abhaya Wewa, had much flatter embankments, and in some cases exceeded four horizontals to one vertical. Author’s Note: Abhaya Reservoir (Ref: Seeing Ceylon, R.L Brohier) “Basawakkulam (Abhaya reservoir) lying in a shallow valley with its waters held up by an earth bund whose concave side faces up-stream claims pride of place as the oldest of the three Anuradhapura city reservoirs. (Nuwara Wewa, Tissa Wewa and Abhaya Wewa). Abhaya reservoir was built after Pandukabhaya, an intelligent young King assumed rule over the kingdom. There is nothing in the structure to indicate its antiquity, but if evidence be needed of the remarkable achievement of that early unnamed hydraulic engineer who designed it, there is proof that this structure remains unbreached even after the thrilling history of Anuradhapura, with its unique records of conquests, dynastic ambitions, regal triumphs and tragedies, had ended on the crest of a mighty wave of invasion 1200 years after the city was founded”. ------------------------------------------------------------------------------------------------ Author’s Note: (Components of a Reservoir): Ancient reservoirs in Sri Lanka (Wewa) have following major components. 1. Bund or embankment to hold water. (Bund is known as “Waw Kandiya” in Sinhalese). 2. Sluice to obtain water from the reservoir. (Sluice is known as “Sorowwa” in Sinhalese). 3. Spill to remove water during major flood events. (Spill is known as “Pitawana” in Sinhalese). Bund: (Built using soil) Figure 1 Ancient reservoir bunds were built with soil. If water flows over the bund, that bund would fail. Water should never be allowed to flow over the bund.
Concise Mahavamsa Ruwan Rajapakse, P.E., Sinhalanet.com 25 Spill (Pitawana): (built using rock) During flood events, water is allowed to go over the spill. Spill is built using rock. Spill will not fail when water goes over it. On the other hand as mentioned earlier, bund would fail if water goes over it, since the bund is built using soil. Bund (soil) Spill (rock) Figure 2 Ancient Engineers had to decide whether the length of the spill is enough to remove all the water during a major flood. If the length of the spill is not enough, water would rise and go over the bund. Then the reservoir bund would fail. As mentioned earlier, water should never be allowed to go over the bund. In the case of Kalawewa, spill was 170 feet long and 216 feet wide!. (Compare this to a length of a soccer field of 300 ft). Early British investigators believed that the spill of Kalawewa was over designed. Later studies proved that the ancient Engineer was right since flood water could accumulate very fast during major flood events and longer and stronger spill is required to remove the water quickly to save the reservoir bund.
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Concise Mahavamsa Ruwan Rajapakse, P.E., Sinhalanet.com 1

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