The map of Sri Lanka is studded with literally thousands of man-made lakes, commonly known as tanks, or wewas (pronounced, and occasionally spelt, “vavas”). The civilization of early Sri Lanka was essentially agricultural, and the need to ensure a regular supply of water for rice cultivation posed a crucial problem given the location of the island’s early capitals in the dry plains of the north. The climate in these parts – a harsh contrast of famine and plenty, with brief monsoonal deluges separated by long periods of drought – made the use of irrigation, based on the storage of water for the regular cultivation of wet fields, a vital element in early Sinhalese civilization – one which, once mastered, succeeded in transforming the island’s arid northern plains into an enormous rice bowl capable of supporting a burgeoning population.
The first, modest examples of hydraulic engineering date back to the earliest days of Sinhalese settlement in the third century BC, when farmers began to dam rivers and store water in small village reservoirs. With the later increase in royal power, Sri Lanka’s kings began to take an active role in irrigation schemes, while Sinhalese engineers mastered the technology which allowed water in tanks to be stored until needed, then released through sluice gates and channelled through canals to distant fields.
The first giant reservoirs were constructed in the reign of Mahasena (274–301), who oversaw the construction of some sixteen major tanks, including the Minneriya tank, and Dhatusena (455–473), who constructed the remarkable Jaya Ganga canal, almost 90km long and maintaining a subtle gradient of six inches to the mile, which delivered water to Anuradhapura from the huge Kalawewa – whose waters ultimately hastened that unfortunate king’s demise (see Sigiriya Rock). Further tanks and canals were built during to the reigns of Mogallana II (531–551), whose Padaviya tank, in the northern Vavuniya district, was the largest ever constructed in ancient Sri Lanka, and Aggabodhi II (604–614), who was responsible for the tank at Giritale, amongst other works.
The construction of large-scale irrigation works became a defining feature of early Sinhalese civilization, while the maintenance of such massive hydraulic feats required skilled engineering and a highly evolved bureaucracy. The captured waters allowed a second rice crop to be grown each year, as well as additional vegetables and pulses, all of which supported much higher population densities than would otherwise have been possible. The surplus agricultural produce created by large-scale irrigation and the taxes raised from the system were major sources of royal revenue, allowing expansive building works at home and military campaigns overseas culminating in the reign of the Polonnaruwan king, Parakramabahu I, who famously declared that “not one drop of water must flow into the ocean without serving the purposes of man”, and who oversaw the creation of the vast Parakrama Samudra at Polonnaruwa, one of the last but finest monuments of ancient Sinhalese irrigation.