Grand Anicut

Kallanai Dam
The present structure of the dam
Location of Kallanai Dam in India Tamil Nadu
Official name	Kallanai Dam
Location	Trichy District
Coordinates	10°49′49″N 78°49′08″E / 10.830166°N 78.818784°E / 10.830166; 78.818784Coordinates: 10°49′49″N 78°49′08″E / 10.830166°N 78.818784°E / 10.830166; 78.818784
Dam and spillways
Type of dam	Composite Dam and Reservoir
Impounds	Cauvery
Length	0.329 km (1,079 ft)
Width (base)	20 m (66 ft)

Kallanai (also known as the Grand Anicut , Tamil : கல்லணை) is an ancient dam, which is built (in running water) across the Kaveri river in Trichy District in the state of Tamil Nadu in South India. Located at a distance of 15 km from Tiruchirapalli, the dam was originally constructed by the Chola king Karikalan in 2nd century AD. It is located on Kaveri river approximately 20 KM from Trichy, but the dam falls under Thanjavur district . and is the fourth-oldest water-diversion or water-regulator structures in the world which is still in use.

The dam was originally built by Karikalan about 2000 years ago.The idea behind the construction of the dam was to divert the river to the delta districts thereby boosting irrigation. The dam was re-modeled by the British during the 19th century. In 1804, Captain Caldwell, a military engineer, was appointed by the British to make a study on the Kaveri river and promote irrigation for the delta region. He found that a large amount of water passed onto the Kollidam leaving behind a small volume for irrigation purposes. Caldwell initially proposed a solution by raising the dam and hence raised the dam stones to a height of 69 centimetres (27 in), thus increasing the capacity of the dam. Following this, Major Sim proposed the idea of undersluices across the river with outlets leading to the Kollidam River (Coleroon) thus preventing formation of silt. The Lower Anaicut built by Sir Arthur Cotton in 19th century CE across Coleroon, the major tributary of Cauvery, is said to be a replicated structure of Kallanai.