Major dams of India: the tallest, the longest and the oldest

Dams hold back river water to create large reservoirs that provide irrigation, drinking water, electricity and protection from floods. After independence Jawaharlal Nehru called big dams "the temples of modern India". Here are the major dams of India with their rivers, states and special features — for exams and for general knowledge.

India's major dams at a glance

The tallest: Tehri Dam

Tehri Dam on the Bhagirathi in Uttarakhand is about 260 metres tall — India's tallest dam and one of the tallest in the world. It is an earth-and-rockfill dam. It generates electricity and supplies drinking and irrigation water to Delhi and Uttar Pradesh. The old town of Tehri was submerged in its reservoir, and its people were resettled in New Tehri.

The longest: Hirakud Dam

Hirakud Dam on the Mahanadi near Sambalpur in Odisha was completed in 1957. With the main dam and the earthen dykes on both sides, it is about 26 kilometres long, which is why it is counted among the longest dams in the world. It has largely stopped the floods that used to strike the Mahanadi delta again and again.

Types of dams

By their design, dams are mainly of three kinds. A gravity dam holds back water by its sheer weight — Bhakra and Nagarjuna Sagar are examples. An arch dam is curved like an arch and passes the water's pressure onto the rock on both sides — Idukki is one. Earth-and-rockfill dams are built where solid rock lies very deep — Tehri and the dykes of Hirakud are of this type. Every dam has a "spillway", so that extra water can be let out safely during floods.

Did you know? The "Kallanai" (Grand Anicut) on the Kaveri in Tamil Nadu is believed to have been built about two thousand years ago, in the time of the Chola king Karikalan. It is among the oldest water-control structures in the world that are still in use.

The benefits and the challenges of dams

• Benefits: irrigation boosted farming (Bhakra played a big part in the Green Revolution), hydropower became available, cities got water and floods were controlled.
• Displacement: big reservoirs drown villages and fields, forcing lakhs of people to leave their homes. The "Narmada Bachao Andolan" against the Narmada dams arose over this issue.
• Environment: changing a river's flow affects fish and river life, and silt settling in reservoirs reduces their capacity.
• Safety: the "Dam Safety Act" was passed in 2021 to look after the upkeep of old dams.

India has more than 5,000 large dams — third in number after China and the United States. Read about the huge lakes formed by dams in Which is the largest lake in India.

Read about the rivers in Major rivers of India · More articles: Geography · Practise: Geography questions.