Man-made lakes: ancient heritage and modern biological resource

Abstract

The most substantial remains of the ancient civilization of Sri Lanka which date back to 600 BC, are the numerous man-made lakes. These comprised a well integrated irrigation system unmatched for its engineering sophistication in ancient times. This system of irrigation largely was abandoned around AD 1200 and was `discovered' by observers only about 200 years ago. Large surface areas >1,000 ha−1, sophisticated sluices for drawing water out, and well engineered channels and river dams reached construction standards which have excited the wonder of modern engineers. Rural settlements were centred around small reservoirs (called tanks after the Portuguese Tanqué) and the village came to be synonymous (in Sinhalese) with tank. The high density of reservoirs and adjacent ricefields indicate human densities which have been estimated at as high as 70 million. A more reasonable estimate of peak human density is around 4--6 million, still a very high density in ancient times for a country with only 65,000 km2, of which about half was unoccupied hill country. Although large urban centres were few, they were well organized. The irrigation system was the basis for rice cultivation, and life was affluent.