Pachaiyar River originates on the eastern slopes of the Western Ghats

Western Ghats

The Western Ghats, Western Ghauts or the Sahyādri is a mountain range along the western side of India. It runs north to south along the western edge of the Deccan Plateau, and separates the plateau from a narrow coastal plain along the Arabian Sea. The Western Ghats block rainfall to the Deccan...

 approximately 1000 m above sea level in the state of Tamil Nadu

Tamil Nadu

Tamil Nadu is one of the 28 states of India. Its capital and largest city is Chennai. Tamil Nadu lies in the southernmost part of the Indian Peninsula and is bordered by the union territory of Pondicherry, and the states of Kerala, Karnataka, and Andhra Pradesh...

 in southern India. It then converges with the Tambaraparani River. Nine anicuts have been built across it before it loses its identity in the Tamiraparani.

The total length of the river from its origin to its merger with the Tamiraparani is about 32 km.