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About kalawewa:
Kala Wewa built by the King Datusena in 460 A.D, is a twin reservoir complex (Kala Wewa & Balalu Wewa) which has a capacity of 123 million cubic meters. This reservoir complex has facilitated with a stone made spillway and three main sluices. From the central major sluice, a 40 feet wide central conveys water to feed thousands of acres of paddy lands and ends at the historical capital Anuradhapura city tank Tissa Wewa meandering over 87 km at a slope of 6 inches per mile and is another wonder of primeval hydraulic engineering facility in ancient Ceylon.

Size
Its circumference is 40 miles and has a total area of 7 square miles at full capacity.Length of the dam is 22,572 feet and the height is 48 feet .

History
This reservoir was built by the King Dhathusena who ruled the country during 455 – 473 CE in the 5th century.
Tamil invaders who arrived from South India ruled the north part of the country during the period from 429 to 455 AD. King Dhathusena defeated the invaders and united the country and then he wanted to rebuild the irrigation system by constructing several tanks, canals, etc., in and round the kingdom of Anuradhapura.
After completion of construction of Kala Wewa, the king built another tank called Balalu Wewa nearby and connected the two tanks together making the biggest tank in Sri Lanka.[2]King Mahinda II who ruled the country during 777 – 797 CE expanded the tank further. Water of the tank was transferred to the Thisa Wewa in Anuradhapura by an ancient 54 miles long canal called Jaya Ganga alias Yodha Ela which has a fine slope of one foot per mile but according to some historians it is one inch per mile.

Renovation
First restoration to the tank is done by King Parakramabahu I in the 12th century.
The tank was renovated several times in the past as in the period of British Governor Sir William Henry Gregory (1872–1877
and Sir Arthur Hamilton-Gordon (1883–1890).
After the British rule in the country and in 1958, the tank's bund was reconstructed connecting the tank with Balalu Wewa.

Attraction
There is a 12 meter high standing statue of Buddha created by king dhathusena. This statue is named after the village it is situated so it is called Avukana Buddha statue and it can be seen over-looking at the tank near by.

Purpose
The reservoir served as one of largest irrigation tanks in ancient time. While supplying water also for the small tanks in rural areas on the way, the canal Jaya Ganga carried water from Kala Wewa and stored enough water in the Thisā Wewa for the population of then capital city of Anuradhapura.well
Being one of main storages in the Mahaweli Irrigation Scheme since 1976, the tank serves to the population in the North Central Sri Lanka. It is used for fresh water fishing and the flora, specially the grasses in its valley, is the main sources of silage for the herds of cattle in the area.