eastern coastal lowlands of Tamil Nadu (Tamil Nādu) state, southern India. Bounded by the Andhra plains to the north, the Bay of Bengal (Bengal, Bay of) to the east, the Indian Ocean to the south, and the Eastern Ghats to the west, the Tamilnad Plains consist of the Kaveri (Cauvery) River (Kaveri River) delta and the deltas of the Vaigai (Vaigai River) and Palar (Palar River) rivers, which have formed sand and shingle beaches.

Sand dunes (locally known as theris) rising 100 to 215 feet (30 to 65 metres) and supporting palmyra palm and thorny scrub are conspicuous features along the relatively straight coast. The flat plains are broken by numerous hills with a distinct north-northeast to south-southwest trend. Natural vegetation consists of littoral forests and plantations of casuarina and coconut, together with scattered trees, climbing vines, and grass. The Kaveri, Ponnaiyar (Ponnaiyar River), Palar (Palar River), Vaigai (Vaigai River), Tambraparni, Vellar, and Arni rivers flow east into the Bay of Bengal. The soils are red-loamy and sandy-loamy, both rich in iron. Agriculture is the mainstay of the economy of the region; crops include rice, pulses (legumes), oilseeds, tobacco, and sugarcane. The Kaveri delta has a large irrigation canal system.

The early development of industry by the British has made the coast of the Tamilnad Plains one of the most industrialized areas in India; factories produce textiles, cement, chemicals, vegetable oil, fertilizers, automobiles, galvanized pipe, and electronic equipment. The railway coach facility at Perambur is one of the largest in Asia. The town of Neyveli has a large thermal power plant. Railways and roads connect Chennai (Madras), Tiruchchirappalli, Tirunelveli, Thanjavur, and Chengalpattu.