River Pachaiyar originates at an altitude of 1000 m above sea level on the eastern slope of the Western Ghats, at about 11 km to the north west of Kalakadu. It is a tributary of Tamiraparani and makes its confluence with the river in the village of Tharuvai. Between its source and the point of confluence, Pachaiyar traverses a total distance of 32 km. Kavayan Odai, Anaikidangu Odai and Uppan Odai are its main tributaries.
