Which is the longest dam in India?
Option 3 is the right answer.
Hirakud Dam built on Mahanadi River is the longest dam in India. The overall length of the main dam is 4.8 km, and the total length is 25.8km with dam and dykes taken together. The dam is about 15 km upstream of Sambalpur town in State of Orissa and was the first post independence major multipurpose river valley project in India. The dam irrigates 436000 ha of CCA in Mahanadi delta and has an installed capacity of 307.5 MW. Hirakud Dam is a composite structure of Earth, Concrete and Masonry. Hirakud Dam intercepts 83400 sq. km (32200 sq miles) of Mahanadi catchments. It has a reservoir spread of 743 sq km at full reservoir level and the reservoir has a storage of 5818 M. Cum with gross of 8136 M Cum.