Rapti Zone was one of the fourteen zones, located in the Mid-Western Development Region of Nepal. It was named after the West Rapti River which drains Rolpa, Pyuthan and part of Dang districts. The remainder of Dang and part of Salyan district are drained by the Babai. The remainder of Salyan and all of Rukum districts are drained by the Bheri.

The West Rapti, also known as the Kuwano, is a river which drains Rapti Zone in Mid-Western Region, Nepal, then Awadh and Bhojpur-Purvanchal regions of Uttar Pradesh state, and finally India before joining the Ghaghara. It is a major left bank tributary of the Ganges, and is also known as the Karnali in Nepal.