The Thamirabarani or Tamraparni or Porunai is a perennial river that originates from the Agastyarkoodam peak of Pothigai hills of the Western Ghats, above Papanasam in the Ambasamudram taluk. It flows through Tirunelveli and Thoothukudi districts of the Tamil Nadu state of southern India into the Gulf of Mannar. It was called the Tamraparni River in the pre-classical period, a name it lent to the island of Sri Lanka. The old Tamil name of the river is Porunai. From the source to sea, the river is about 128 kilometres (80 mi) long and is the only perennial river in Tamil Nadu. This river flows towards north direction initially. However, it changes to east direction later.

Tirunelveli district is one of the 38 districts of Tamil Nadu state in India. It is the largest district in terms of area with Tirunelveli as its headquarters. The district was formed on 1 September 1790 by the British East India Company, and comprised the present Tirunelveli and Thoothukudi, Tenkasi and parts of Virudhunagar and Ramanathapuram district. As of 2011, the undivided district had a population of 3,077,233.