The Rapti rises south of a prominent E-W ridgeline midway between the western Dhaulagiri Himalaya and the Mahabharat Range. A summit on this ridgeline marks a triple divide. North of the triple divide the Karnali and Gandaki basins are adjacent; south of it the Rapti and similar but smaller Babai River (; ) separate the two larger basins. After crossing into India, the Babai and Rapti separately join the Karnali's continuation called Ghaghara. The Ghaghara ultimately joins the Ganges.