Over a surface area of 65,600 km2, 19.5 million people live in the country. Water bodies, a considerable portion of which are man-made, cover about 4 percent of the land. The terrain of the island is mostly made up of coastal plains, with mountains rising only in the south central part.
Sri Lanka is a classic example of the "hydraulic civilization" which had developed in the ancient period. With the immigration of Aryans from Eastern India to Lanka in 543 BC, cultivation of rice developed into a grand scale in the island. As the new essentially agricultural Aryan civilization flourished, increasingly ambitious projects of irrigation were launched at a pace with a view to harness the monsoon rains. It can be safely deduced that the first great reservoirs ever in the world were built in Sri Lanka. Since the great lakes of Egypt, being merely natural hollows into which streams were turned do not fall into the category of man-made rainwater reservoirs as those of in Sri Lanka.
The rainwater reservoirs developed in the ancient kingdom of Anuradhapura (437 BC-845 AD) & Polonnaruwa (846 AD-1302 AD), Dry Zone of central lowlands resulted in two season of farming while the Wet Zone remained sparsely populated and covered by thick forests. Today around 12,000 ancient small dams & nearly 320 ancient large dams together with thousands of man-made lakes dot the lowlands, with over 10,000 reservoirs in the Northern Province alone. Today Ancient Sinhalese irrigation supplemented by Modern Irrigation Projects continues to provide the self-sufficiency in cultivation of rice, which is the major food of the Sri Lankans.
"Many are the instances where the modern engineer has frequently found himself anticipated by an unnamed predecessor" Ceylonese historian R. L Brohier