<P> Hirakud Dam is built across the Mahanadi River, about 15 kilometres (9.3 mi) from Sambalpur in the state of Odisha in India . Behind the dam extends a lake, Hirakud Reservoir, 55 km (34 mi) long . It is one of the first major multipurpose river valley projects started after India's independence . </P> <P> Before the devastating floods of 1936, Sir M. Visveswararya proposed a detailed investigation for storage reservoirs in the Mahanadi basin to tackle the problem of floods in the Mahanadi delta . In 1945, under the chairmanship of Dr. B.R. Ambedkar, the Member of Labour, it was decided to invest in the potential benefits of controlling the Mahanadi for multi-purpose use . The Central Waterways, Irrigation and Navigation Commission took up the work . On 15 Mar 1946, Sir Hawthorne Lewis, the Governor of Odisha, laid the foundation stone of the Hirakud Dam . A project report was submitted to the government in June 1947 . Pandit Jawaharlal Nehru laid the first batch of concrete on 12 April 1948 . </P> <P> In 1952, Mazumdar Committe was appointed by the government to oversee the soundness and technical feasibility of the project . The committee was envisaged a cost of ₹ 92.80 crore for the project and that the construction of the main dam would be complete by June 1955 . It also said that by 1954--55 a total of 1,347,000 acres (545,000 ha) would be irrigated and that 48 GW of electric power would be generated . However, the dam was completed in 1953 and was formally inaugurated by Prime Minister Jawaharlal Nehru on 13 January 1957 . The total cost of the project was ₹ 1,000.2 million (equivalent to ₹ 71 billion or US $1.0 billion in 2017) in 1957 . Power generation along with agricultural irrigation started in 1956, achieving full potential in 1966 . </P> <Table> Technical Details <Tr> <Td> Total Length </Td> <Td> 25.79 km (16.03 mi) </Td> </Tr> <Tr> <Td> Length of Main Dam </Td> <Td> 4.8 km (3.0 mi) </Td> </Tr> <Tr> <Td> Artificial Lake </Td> <Td> 743 km (287 sq mi) </Td> </Tr> <Tr> <Td> Irrigated Area (both crop) </Td> <Td> 2,355 km (235,477 ha) </Td> </Tr> <Tr> <Td> Area lost in construction of Dam </Td> <Td> 596 km (147,363 acres) </Td> </Tr> <Tr> <Td> Installed Capacity (Power Generation) </Td> <Td> 347.5 MW </Td> </Tr> <Tr> <Td> Cost (in 1957) </Td> <Td> ₹ 1,000.2 million (equivalent to ₹ 71 billion or US $1.0 billion in 2017) </Td> </Tr> <Tr> <Td> Top dam level </Td> <Td> R.L. 195.680 m (642 ft) </Td> </Tr> <Tr> <Td> F.R.L / M.W.L </Td> <Td> R.L. 192.024 m (630 ft) </Td> </Tr> <Tr> <Td> Dead storage level </Td> <Td> R.L. 179.830 m (590 ft) </Td> </Tr> <Tr> <Td> Total quantity of earth work in Dam </Td> <Td> 18,100,000 m (640 × 10 ^ cu ft) </Td> </Tr> <Tr> <Td> Total quantity of concrete </Td> <Td> 1,070,000 m (38 × 10 ^ cu ft) </Td> </Tr> <Tr> <Td> Catchment </Td> <Td> 83,400 km (32,200 sq mi) </Td> </Tr> </Table>

Which is the longest river dam in india