of India alongside Hindi. On 17 July 1996, the city known as Madras was officially renamed Chennai, in line with what was then a nationwide trend to using less Anglicised names. On 26 December 2004, an Indian Ocean tsunami lashed the shores of Chennai, killing 206 people in Chennai and permanently altering the coastline. The 2015 Chennai Floods submerged major portions of the city, killing 269 people and resulting in damages of . Environment Geography Chennai is located on the south–eastern coast of India in the north–eastern part of Tamil Nadu on a flat coastal plain known as the Eastern Coastal Plains. Its average elevation is around , and its highest point is . Chennai is south of Delhi, southeast of Mumbai, and southwest of Kolkata by road. Two major rivers flow through Chennai, the Cooum River (or Koovam) through the centre and the Adyar River to the south. A third river, the Kortalaiyar, travels through the northern fringes of the city before draining into the Bay of Bengal, at Ennore. The estuary of this river is heavily polluted with effluents released by the industries in the region. Adyar and Cooum rivers are heavily polluted with effluents and waste from domestic and commercial sources, the Coumm being so heavily polluted it is regarded as the city's eyesore. A protected estuary on the Adyar forms a natural habitat for several species of birds and animals. The Buckingham Canal, inland, runs parallel to the coast, linking the two rivers. The Otteri Nullah, an east–west stream, runs through north Chennai and meets the Buckingham Canal at Basin Bridge. Several lakes of varying size are located on the western fringes of the city. Some areas of the city have the problem of excess iron content in groundwater. Chennai's soil is mostly clay, shale and sandstone. Clay underlies most of the city, chiefly Manali, Kolathur, Maduravoyal, K. K. Nagar, Tambaram, Mudichur, Pallavaram Semmencherry, Alapakkam, Vyasarpadi and Anna Nagar. Sandy areas are found along the river banks and coasts, and include areas such as Tiruvottiyur, George Town, Madhavaram, New Washermanpet, Chepauk, Mylapore, Porur, Adyar, Besant Nagar and Uthandi. In these areas, rainwater runoff percolates quickly through the soil. Areas having hard rock surface include Guindy, Nanganallur, Pallikaranai, Alandur, Jaladampet, Velachery, Adambakkam and a part of Saidapet and Perungudi. The ground water table in Chennai is at 4–5 m below ground in most of the areas, which