This river accounts as the only vital water way in Sistan, and takes its source in the Baba Mountains of Afghanistan.
After following a long course enters the Hamoon Lake, and the water requirements of the plains of Sistan are provided by this river. Other water reserves also depend on the capacity of the Hirmand. The said river is divided into two at the borders of Iran and Afghanistan, and the main branch forms a part of the common borderline between the two countries, before entering Afghanistan.
The other branch is divided into two on Iranian land, one flowing towards Chah Nimeh and the other towards the region of Koohak and Zahak. Two diverging dams have been constructed in these two areas on the river.
In the southern portion of the Sistan plains near the Hirmand, is a large natural pit or hollow which forms a reservoir for irrigation purposes and also is a natural barrier in times of flood, thus preventing damage. The area of this pit is approximately 4,700 hectares.