Rukum district was the northernmost part of Rapti Zone. It is in the basin of Bheri River, a major tributary of the Karnali. Most of Rukum is drained by west-flowing tributaries such as Uttar Ganga draining Dhorpatan Valley and to the north of that the Sani Bheri draining southern slopes of the western DhaulagiriHimalaya. Source : /en.wikipedia.org