The Thamirabarani River is also called Tambaraparani and rises from the eastern slopes of Western Ghats in Tirunelveli district of Tamil Nadu. The river originates from an altitude of two thousand metres above mean sea level in Agasti Hill, which is a part of the Annamalai Range. The peaks of Aduppukkal Mottai, Agathimala and Cherumunji Mottai, are situated near it.

The river then flows through the Tirunelveli and Tuticorin districts. The Thamirabarani River then flows in the east direction and enters the Gulf of Mannar of the Bay of Bengal near Palayakayal. The Thamirabarani River is referred in the ancient Tamil and Sangam texts. The river contains small amount of copper, which gives the river water a distinct reddish tinge. In Tamil, copper is called Thamiram and hence the river is named Thamirabarani. In the past the river was called Podhigai.

The river is 130 kilometers in length and the Thamirabarani basin is situated between latitudes 8.21` N and 9.13` N and between 77.10` E longitudes. The forty metres deep Vanatheertham waterfalls are located near the origin of the Thamirabarani River. The river is feed by its tributaries as well as by monsoons.

The Thamirabarani has several tributaries, which join at different points during its course. The tributaries Peyar, Ullar, Karairar and Pamba joins near the Papanasam Reservoir. A major tributary of Thamirabarani is the Servalar River, which joins at a distance of 22 kilometers from its origin. The Manimuthar River, which originates in the Agathimalai Ranges and joins Thamirabarani near Ambasamudram. Gadana River joins at a distance of 43 kilometres from its origin. The Pachaiyar River joins near Gopalasamudram. The Chittar River flows for seventy-three kilometers before joining the Thamirabarani.

The river flows for 125 kilometers out of which 75 kilometers is in the Tirunelveli district. Along with its tributaries, the river drains an area of 4400 square kilometers.