Kala Wewa
The 928th tallest dam in the world
Kala Wewa (Sinhala:කලා වැව), built by King Datusena in 460 CE, is a reservoir complex consisting of two reservoirs, Kala Wewa and Balalu Wewa. It has the capacity to store 123 million cubic meters of water. The reservoir complex includes a stone made spillway and three main sluices. The main central sluice, 40 feet wide, supplies water to thousands of acres of paddy fields and ends at Tissa Wewa, in the ancient city of Anuradhapura, having meandered over 87 km (54 mi) at a slope of 6 inches per mile. The hydraulic engineering reflects the advanced technology that existed in ancient Sri Lanka.
Dam data from Wikidata (CC0) plus curated additions. Summary from Wikipedia (CC BY-SA).