Sri Lanka has been a country with an agriculture-based economy since ancient times. Historical records indicate that three tribes called Rakshas, Yakkhas, and Nagas were living in Sri Lanka when Prince Wijaya, the founder of the Sinhala nation, landed in Sri Lanka in the 6th Century BC. When he disembarked from his ship, he saw the Yakkha Princess, Kuveni, at a Spinning Wheel beside a tank. It can be seen, however, that tanks existed in pre-Wijayan times.

According to the great chronicle Mahawansha, Anuradhapura is the first great kingdom that lasted more than a millennium in the middle of the dry zone of the country. Ancient engineers of Sri Lanka had constructed tanks to conserve the water received from monsoon rain and from the streams of the area to protect the kingdom from drought. And it was used for the cultivations and needs of the nation, forming one of the great irrigation civilizations in the world. The eco-friendly culture formed under the great leaders of the nation has protected the system for over two millenniums.

All the major old irrigation schemes of Nuwarakalawiya were closely linked with these three rivers called Malwathu Oya, Kala Oya and Modaragam Aru. We might, with good reason, say that although closely linked with these rivers, they take their origin in a magnificent artificial lake described on modern maps as Kala Wewa and Balalu Wewa. These twin tanks were formed by an immense dam thrown across a low valley which held up the waters of the Dambulla Oya, the Mirisgoni Oya and the Hawenella Oya, all of them originally feeders of the Kala Oya. Apart from supplying water to numerous valleys of Nuwarakalawiya for the Purpose of irrigation, there was a time when the very existence of Anuradhapura depended on the water held conserved in this valley.

Kalawewa is one of the great irrigation heritage structures constructed during the Anuradhapura kingdom. It is situated 7 km southwest of Kekirawa in the Anuradhapura district. Present Kalawewa is known as a combination of two ancient tanks called Balaluwewa and Kalawewa. According to the Mahawansha, the older tank, Balaluwewa, was constructed during the period of King Kutakanna Thissa (44-22 BC) across Hawenella Oya, and Kalawewa was constructed during the period of King Dhathusena (453-477 AD) across Kala Oya.

There are a lot of folklores about Kalawewa and its construction. One story says, Kadawara, who found the location and informed King Dhathusena, was in charge of the Kalawewa. One day he found piping in the dam and kept his head against the hole until aid from villages came. And he died. The villages believe the soul of Kadawra, as Kadawara Deviyo still protects Kalawewa and surrounding villages. The devotees of Kadawara still visit the Kadavara Devalaya at the Kalawewa dam. Both investigation and testimony hold that in the past, four major canals or Yodha Ela distributed the water stored in Kala-Balalu Wewa. The illustration; shows two of them. One is known as Balalu Wewa Ela. The other is the Jaya Ganga of the Mahavansa.

Jaya Ganga starts from a sluice at the Kala wewa end of the tank and trails northwards to Anuradhapura and beyond. The bund of this giant channel meanders over the country in easy curves and deflects the water over astonishingly easy gradients. Some idea of this can be measured by the fact that for the first seventeen miles, the fall is not much more than six inches per mile. The Jaya Ganga was not only an engineering marvel but also an ecological system that benefited the public and nature as well. The ancient spill of the twin tank Kala-Balalu Wewa is said to have existed for centuries before it was enlarged in 477 AD. It is a stupendous work of hammered granite, excellently dressed and at the crest morticeed. This ancient spill has been retained untouched in the last scheme of restoration effected in 1877.

The historical records say that the Kala Wewa dam has been breached several times in history, and the reasons are unknown. According to known history, Kala Wewa was restored in 1877 during the period of British Governor Sir William Gregory. Last time, Kalawewa had restored after the breach in 1958 due to the well-known heavy flood which breached more than 1300 tanks all over the country. The last major rehabilitation work done in 1976 had been upgraded the capacity of the Kalawewa to 123 MCM, which was carried out by the Mahaweli Development program to accommodate diverted Mahaweli water.

According to Brohier, there was evidence of four ancient canals stared from the dam. The sluices of them are called Kalawewa Goda Ela, restored in 1887, Balaluwewa Goda Ela restored in 1887, Puliyankulama restored in 1973, and the most popular Yodha Ela sluice was restored in 1885, which are still in use. The Right Bank sluice and Left Bank sluice were constructed in 1976 under the Mahaweli.

The structure represents a milestone / turning points in development of irrigated agriculture and bears an exceptional testimony to development of agriculture and increase in food production along with the improvement of economic condition of farmers;

Kalawewa and its waterway Yodha Ela (Jaya Ganga) is one of the most magnificent achievements of the ancient irrigation engineers of Sri Lanka. The reservoir has a total area of 7200 ACS at the full supply level. Gross storage at the full supply level in 2018 is 104 MCM. The ancient spill is measured to be 602 feet in length. The spill was built using hammered granite, a solid structure one could imagine. Each block of granite is shaped precisely to fit its neighbour. The whole structure eventually acts like one huge rock. The total length of the dam is 6500 m, and the maximum Height above Bed Level is 14.5 m. Yodha Ela has built to bring water from Kala wewa to the city of Anuradhapura (Abhaya wewa, Tissa Wewa and Nuwara Wewa), and the Nachchaduwa reservoir was fed by the Yodha Ela. The length of the Yodha Ela is 87 km. The gradient of Yodha Ela was measured to be 6 inches per mile (1:10,000). Maintaining such a gradient is an extremely challenging task, even for modern engineers who have access to laser-guided survey equipment. Ancient Yoda Ela was later replaced with Nawa Jaya Ganga. As the records, the people of Nuwarakalawiya have benefited from Kalawewa since 477 AD or more. Present, Kalawewa directly feeds 37,485 ha of paddy lands of Mahaweli system “H” and supplies water to Thisa Wewa and so beyond. Although the main purpose of the tank is agriculture, inland fisheries, domestic water supply, and the tourism industry also benefited from it. The Forest reservation upstream of the tank has been declared a national park considering the ecological and historical importance of the location. With the proof of all these historical data, Kalawewa has served the nation for over 1,500 years and has become a landmark heritage structure of the area all over the period. And it is among the great heritage irrigation structures of the world.

The structure made outstanding contribution to enhancing food production, livelihood opportunities, rural prosperity, and poverty alleviation in a region;

Kalawewa and its waterway Yodha Ela (Jaya Ganga) is one of the most magnificent achievements of the ancient irrigation engineers of Sri Lanka. The reservoir has a total area of 7200 ACS at the full supply level. Gross storage at the full supply level in 2018 is 104 MCM. The ancient spill is measured to be 602 feet in length. The spill was built using hammered granite, a solid structure one could imagine. Each block of granite is shaped precisely to fit its neighbour. The whole structure eventually acts like one huge rock. The total length of the dam is 6500 m, and the maximum Height above Bed Level is 14.5 m. Yodha Ela has built to bring water from Kala wewa to the city of Anuradhapura (Abhaya wewa, Tissa Wewa and Nuwara Wewa), and the Nachchaduwa reservoir was fed by the Yodha Ela. The length of the Yodha Ela is 87 km. The gradient of Yodha Ela was measured to be 6 inches per mile (1:10,000). Maintaining such a gradient is an extremely challenging task, even for modern engineers who have access to laser-guided survey equipment. Ancient Yoda Ela was later replaced with Nawa Jaya Ganga. As the records, the people of Nuwarakalawiya have benefited from Kalawewa since 477 AD or more. Present, Kalawewa directly feeds 37,485 ha of paddy lands of Mahaweli system “H” and supplies water to Thisa Wewa and so beyond. Although the main purpose of the tank is agriculture, inland fisheries, domestic water supply, and the tourism industry also benefited from it. The Forest reservation upstream of the tank has been declared a national park considering the ecological and historical importance of the location. With the proof of all these historical data, Kalawewa has served the nation for over 1,500 years and has become a landmark heritage structure of the area all over the period. And it is among the great heritage irrigation structures of the world.

The structure contributed to the evolution of efficient and contemporary engineering theories and practices;

Kalawewa and its waterway Yodha Ela (Jaya Ganga) is one of the most magnificent achievements of the ancient irrigation engineers of Sri Lanka. The reservoir has a total area of 7200 ACS at the full supply level. Gross storage at the full supply level in 2018 is 104 MCM. The ancient spill is measured to be 602 feet in length. The spill was built using hammered granite, a solid structure one could imagine. Each block of granite is shaped precisely to fit its neighbour. The whole structure eventually acts like one huge rock. The total length of the dam is 6500 m, and the maximum Height above Bed Level is 14.5 m. Yodha Ela has built to bring water from Kala wewa to the city of Anuradhapura (Abhaya wewa, Tissa Wewa and Nuwara Wewa), and the Nachchaduwa reservoir was fed by the Yodha Ela. The length of the Yodha Ela is 87 km. The gradient of Yodha Ela was measured to be 6 inches per mile (1:10,000). Maintaining such a gradient is an extremely challenging task, even for modern engineers who have access to laser-guided survey equipment. Ancient Yoda Ela was later replaced with Nawa Jaya Ganga. As the records, the people of Nuwarakalawiya have benefited from Kalawewa since 477 AD or more. Present, Kalawewa directly feeds 37,485 ha of paddy lands of Mahaweli system “H” and supplies water to Thisa Wewa and so beyond. Although the main purpose of the tank is agriculture, inland fisheries, domestic water supply, and the tourism industry also benefited from it. The Forest reservation upstream of the tank has been declared a national park considering the ecological and historical importance of the location. With the proof of all these historical data, Kalawewa has served the nation for over 1,500 years and has become a landmark heritage structure of the area all over the period. And it is among the great heritage irrigation structures of the world.

The structure was unique in some positive and constructive way;

Kalawewa and its waterway Yodha Ela (Jaya Ganga) is one of the most magnificent achievements of the ancient irrigation engineers of Sri Lanka. The reservoir has a total area of 7200 ACS at the full supply level. Gross storage at the full supply level in 2018 is 104 MCM. The ancient spill is measured to be 602 feet in length. The spill was built using hammered granite, a solid structure one could imagine. Each block of granite is shaped precisely to fit its neighbour. The whole structure eventually acts like one huge rock. The total length of the dam is 6500 m, and the maximum Height above Bed Level is 14.5 m. Yodha Ela has built to bring water from Kala wewa to the city of Anuradhapura (Abhaya wewa, Tissa Wewa and Nuwara Wewa), and the Nachchaduwa reservoir was fed by the Yodha Ela. The length of the Yodha Ela is 87 km. The gradient of Yodha Ela was measured to be 6 inches per mile (1:10,000). Maintaining such a gradient is an extremely challenging task, even for modern engineers who have access to laser-guided survey equipment. Ancient Yoda Ela was later replaced with Nawa Jaya Ganga. As the records, the people of Nuwarakalawiya have benefited from Kalawewa since 477 AD or more. Present, Kalawewa directly feeds 37,485 ha of paddy lands of Mahaweli system “H” and supplies water to Thisa Wewa and so beyond. Although the main purpose of the tank is agriculture, inland fisheries, domestic water supply, and the tourism industry also benefited from it. The Forest reservation upstream of the tank has been declared a national park considering the ecological and historical importance of the location. With the proof of all these historical data, Kalawewa has served the nation for over 1,500 years and has become a landmark heritage structure of the area all over the period. And it is among the great heritage irrigation structures of the world.

The structure bears the stamp of a cultural tradition or a civilization of past;

Kalawewa and its waterway Yodha Ela (Jaya Ganga) is one of the most magnificent achievements of the ancient irrigation engineers of Sri Lanka. The reservoir has a total area of 7200 ACS at the full supply level. Gross storage at the full supply level in 2018 is 104 MCM. The ancient spill is measured to be 602 feet in length. The spill was built using hammered granite, a solid structure one could imagine. Each block of granite is shaped precisely to fit its neighbour. The whole structure eventually acts like one huge rock. The total length of the dam is 6500 m, and the maximum Height above Bed Level is 14.5 m. Yodha Ela has built to bring water from Kala wewa to the city of Anuradhapura (Abhaya wewa, Tissa Wewa and Nuwara Wewa), and the Nachchaduwa reservoir was fed by the Yodha Ela. The length of the Yodha Ela is 87 km. The gradient of Yodha Ela was measured to be 6 inches per mile (1:10,000). Maintaining such a gradient is an extremely challenging task, even for modern engineers who have access to laser-guided survey equipment. Ancient Yoda Ela was later replaced with Nawa Jaya Ganga. As the records, the people of Nuwarakalawiya have benefited from Kalawewa since 477 AD or more. Present, Kalawewa directly feeds 37,485 ha of paddy lands of Mahaweli system “H” and supplies water to Thisa Wewa and so beyond. Although the main purpose of the tank is agriculture, inland fisheries, domestic water supply, and the tourism industry also benefited from it. The Forest reservation upstream of the tank has been declared a national park considering the ecological and historical importance of the location. With the proof of all these historical data, Kalawewa has served the nation for over 1,500 years and has become a landmark heritage structure of the area all over the period. And it is among the great heritage irrigation structures of the world.

Engineering utility vis-à-vis designed utility

Kalawewa is situated northwest of Dambulla, downstream of Dambuluoya and Kandalama reservoirs. The catchment area of the lake is 552 km2, and the Gross storage up to FSL IS 104 MCM. The full Supply Level of the lake is 129.235 m (424 ft.) above MSL, and the Probable Maximum Flood is 133.28 m above MSL. The dam is constructed as a Homogenous Earth fill embankment. The Length along Crest is 6.5 km, and the Maximum Height above Bed Level is 14.5 m. The main river that flows into the Kalawewa reservoir is Kalaoya which collects water from an area of 525  km2  of the local catchment of the reservoir. The Mahaweli water diverted from Bowathenna flows into the bifurcation at the Lenadora via irrigation tunnel of Bowathenna dam and diverted into Dambuluoya and feeds Dambuluoya reservoir. From the Dambuluoya reservoir, water is diverted to Kalawewa through Kalaoya.

Present State of Conservation

The historical records say that the Kala Wewa dam had been breached 3 or 4 times, and the reasons are still unknown. According to known history, Kala Wewa was restored in 1877 during the period of British Governor Sir William Gregory. Last time, Kalawewa had restored after the breach in 1958 due to the well-known heavy flood which breached more than 1300 tanks all over the country. At last, major rehabilitation works of Kalawewa were carried out by the Mahaweli Development program in 1976 when the spillway was raised to accommodate Mahaweli water diverted from Polgolla. The gross storage was then increased to 123 MCM.

The sluice of Kalawewa Goda Ela was restored in 1887, Balaluwewa Goda Ela was restored in 1887, Puliyankulama was restored in 1973, and the most popular Yodha Ela sluice was restored in 1885, which are still in use. The Right Bank sluice and Left Bank sluice were constructed in 1976 under the Mahaweli Development program.

Twenty-one piezometers are installed by the Water Resources Board under the consultancy of the Central Engineering Consultancy Bureau (CECB) in the year 1989. 3 number of piezometers are installed by the MRRP project. Another six piezometers were installed by Dam Safety and Water Resources Planning Project (DSWRPP), funded by World Bank in the year 2012. Major rehabilitation items attended under DSWRPP are supplying and installation of levelling monuments, supplying and installation of piezometers, furnishing and installation of V – notch and pipe culvert, renovation of rip rap, renovation of toe drain and access road, renovation of spillway gates, left bank sluice, Balaluwewa Goda Ela sluice, Kalawewa yoda ela sluice, Kala wewa Goda Ela sluice and Jayaganga sluice.