Sistan Basin

The Sistan Basin is an inland endorheic basin encompassing large parts of southwestern Afghanistan and minor parts of southeastern Iran, one of the driest regions in the world and an area subjected to prolonged droughts. Its watershed is a system of rivers flowing from the highlands of Afghanistan into freshwater lakes and marshes and then to its ultimate destination: Afghanistan's saline Godzareh depression, part of the extensive Sistan terminal basin. The Helmand River drains the basin's largest watershed, fed mainly by snowmelt from the mountains of Hindu Kush, but other rivers contribute also.

A basalt hill, known as Mount Khajeh, rises beside the lakes and marshes of the basin.

The lowest part of the Sistan Basin contains a series of shallow lakes, known as hamuns. It appears that in the past there was a single Hamun Lake, but there are now three separate lakes. From north to south the lakes are:

The Hamun-e Puzak lies mostly in Afghanistan. It receives water from the Shelah Charkh channel of the Helmand River, and also from the Khash River and other small rivers.

The Hamun-e Sabari is split between Iran and Afghanistan. It receives water from the Parian branch of Helmand River, the Farah River and the Harut River.

The largest proportion of the Helmand River's waters flow into the Hamun-e Helmand, which is entirely in Iran, by a channel known as the Rud-e Sistan.

In times of flood the hamuns join into one large lake, and once every 20 years or so the floodwaters create an overflow from the Hamun-e Helmand by a normally dry river known as the Shela Rud, terminating in the Godzareh depression. In 1885 there was an exceptional flood, and the floodwaters filled the depression for three years.

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