Helmand River

The Helmand River (also spelled Helmend, or Helmund, Hirmand; Pashto/Persian: ; Greek: ' ("Etýmandros"); Latin: ') is the longest river in Afghanistan and the primary watershed for the endorheic Sistan Basin.
Etymology.
The name comes from the Avestan "Haētumant", literally "dammed, having a dam", which referred to the Helmand River and the irrigated areas around it.
Geography.
The Helmand River stretches for . It rises in the Hindu Kush mountains, about 40 km west of Kabul (), passing north of the Unai Pass, in the eastern proximities of Hazarajat, in Behsud, Maidan Wardak, flows west to Daykundi and Uruzgan. It crosses south-west through the desert of Dashti Margo, to the Sistan marshes and the Hamun-i-Helmand lake region around Zabol at the Afghan-Iranian border (). A few smaller rivers such as Tarnak and Arghandab flow into Helmand.
This river, managed by the Helmand and Arghandab Valley Authority is used extensively for irrigation, although a buildup of mineral salts has decreased its usefulness in watering crops. For much of its length, Helmand is free of salt. Its waters are essential for farmers in Afghanistan, but it feeds into Lake Hamun and is also important to farmers in Iran's southeastern Sistan and Baluchistan province.
A number of hydroelectric dams have created artificial reservoirs on some of the Afghanistan's rivers including the Kajakai Dam on the Helmand River. The chief tributary of the Helmand river is the Arghandab River (confluence at ) which also has a major dam north of Kandahar.
History.
The Helmand valley region is mentioned by name in the Avesta ("Fargard" 1:13) as the Aryan land of "Haetumant", one of the early centres of the Zoroastrian faith in areas that are now Afghanistan. However, by the late first millennium BC and early first millennium AD, the preponderance of communities of Hindus and Buddhists in the Helmand and Kabul valleys led to Parthians referring to it as "White-India". 