The Grand Anicut, also known as the [கல்லணை] Kallanai, is an ancient dam built on the Kaveri River in the state of Tamil Nadu in southern India.
It was built by the Chola king Karikalan around the 1st Century AD and is considered one of the oldest water-diversion or water-regulator structures in the world, which is still in use.
The Kaveri River forms the boundary between the Erode and Salem districts. The Bhavani River joins the Kaveri at the town of Bhavani, where the Sangameswarar Temple, an important pilgrimage spot in Tamil Nadu, was built at the confluence of the two rivers. Sweeping past the historic rock of Tiruchirapalli, it breaks into two channels at the island of Srirangam, which enclose between them the delta of Thanjavur (Tanjore), the garden of Tamil Nadu. The northern channel is called the Kollidam (Kolidam); the other preserves the name of Kaveri, and empties into the Bay of Bengal at Poompuhar, a few hundred miles south of Chennai(Madras). On the seaward face of its delta are the seaports of Nagapattinam and Karaikal. Irrigation works have been constructed in the delta for over 2,000 years.
The Kallanai is a massive dam of unhewn stone, 329 metres (1,080 ft) long and 20 metres (60 ft) wide, across the main stream of the Kaveri. The purpose of the dam was to divert the waters of the Kaveri across the fertile Delta region for irrigation via canals. The dam is still in excellent repair, and supplied a model to later engineers, including the Sir Arthur Cotton’s 19th-century dam across the Kollidam, the major tributary of the Kaveri. The area irrigated by the ancient irrigation network is about 1,000,000 acres (4,000 square kilometres). Recently the Delta farmers of Tamil Nadu demanded the Tamil Nadu government honour the great Chola king Karikalan, who built the Kallanai. his dam is a buttress dam
Source: By Niranjan Shah