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Helmund(both: hĕl`mənd), river, c.700 mi (1,130 km) long, rising in the Hindu Kush Mts., NE Afghanistan and flowing generally SW to the Sistan basin, SW Afghanistan, where it helps form the Hamun-i-Helmand (Sistan Lake), a marshy lake that extends into Iran; longest river in Afghanistan. The Arghandab is its chief tributary. The Helmand's ancient irrigation and river-control system was destroyed by Jenghiz Khan (13th cent.) and Timur (14th cent.); the modern irrigation works are vital to both Iranians and Afghans, and in times of drought there are disputes over water rights. The Helmand Valley Authority extensively developed the region, improving irrigation and flood control. The name also occurs as Hilmand and Hirmand.
or Hilmand, a river in Afghanistan that flows through the Iranian plateau. Length, 1,150 km; basin area, about 500,000 sq km. Its source is in the Koh-i-Baba, and it flows into the Hamun lakes in Iran, forming a delta in which its branches are constantly changing course. Its major tributary is the Arghandab. It is fed chiefly by snow runoff. Its waters are high in the spring and summer, and low in the winter (although thaws sometimes cause the river to rise in the winter). Its average annual volume ranges from 400 to 500 cu m per sec; during the high season it ranges from 1,500 to 2,000 cu m per sec, with a maximum of over 15,000 cu m per sec, and winter flow is 50 to 60 cu m per sec. Its middle and lower course irrigate a small strip of land between the Registan and Dasht-i-Margo deserts, including the Girishk Oasis and the major settlement of Girishk. The delta region of the Helmand is heavily populated; its waters are used for irrigation. Several dams have been built on branches of the Helmand, the most important being the Seistan Dam.