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Sistan Basin

geography Maturity 5-7 Next article →

The Sistan Basin is a massive inland endorheic basin. An endorheic basin is a land area where water does not flow to the ocean. Instead, water collects in internal lakes or marshes. This basin covers parts of southwestern Afghanistan and southeastern Iran. It is one of the driest regions on Earth. It is often subject to very long periods of drought.

Helmandrivermap
Helmandrivermap

The basin's watershed is a complex system of rivers. These rivers flow from high mountains into freshwater lakes. Eventually, the water reaches the saline Godzareh Depression. This depression is part of the larger Sistan terminal basin.

The hydrology of the basin depends on the Helmand River. This river drains the largest watershed in the area. It is fed mainly by snowmelt from the Hindu Kush mountains. Other smaller rivers also contribute water to the system. At the lowest point of the basin, several shallow lakes exist. These lakes are called hamuns. In the past, there may have been a single Hamun Lake. Today, there are three distinct lakes.

Helmandrivermap
Helmandrivermap

The three hamun lakes have specific locations and water sources. The first is Hamun-e Puzak, which sits mostly in Afghanistan. It receives water from the Khash River and the Shelah Charkh channel. The second is Hamun-e Sabari, which is split between Afghanistan and Iran. It is fed by the Farah River, the Harut River, and the Parian branch of the Helmand. The third is the largest, Hamun-e Hirmand, located entirely in Iran. Most of the Helmand River's water flows into this lake via the Rud-e Sistan channel.

Water levels in these lakes change dramatically over time. During periods of heavy flooding, the hamuns join into one large lake. Roughly once every 20 years, floods create an overflow. This overflow travels through the Shela Rud, a normally dry river. This water then terminates in the Godzareh Depression. In 1885, an exceptional flood filled that depression for three years. However, recent years have seen the opposite effect. During a drought from 1998 to 2005, the hamuns dried up completely.

The ecology and economy of the region rely on these wetlands. Local people depend on agriculture for their survival. This farming requires snowmelt and rainfall from high mountains. The water supply fluctuates severely, creating survival problems for human settlements. The wetlands also provide vital raw materials. For example, reed beds provide food for livestock. People also use reeds for cooking fuel and heating fuel. Reeds are used to build structures and create various handicrafts.

When water is available, fishing and hunting provide important income. When the drought arrived, the local economy collapsed. This also destroyed the ecological system and damaged irrigation in the Helmand delta.

The Sistan Basin has a very deep history of human habitation. Sophisticated cultures have lived here for more than 5,000 years. One notable site is Shahr-e Sukhteh, or the "Burnt City," in Iran. It was built in 3100 B.C. near a branch of the Helmand River. People likely abandoned it 1,000 years later due to climate changes. Another Bronze Age site, Shahdad, is located further west near the Lut desert. In Afghanistan, the medieval hubs of Kang and Zaranj are now covered by sand.

Archaeologists have found many significant remains throughout the basin. In the Dasht-e Margo and Chakhansur areas, old irrigation canals are still visible. Elsewhere, sand has buried agricultural fields and filled canals with silt. On Mount Khajeh, a basalt hill, researchers found a citadel complex. They also found the remains of a Zoroastrian fire temple. Other major sites include Dahan-e Gholaman, a likely capital of the ancient satrapy of Zranka. Ram Shahristan was another ancient capital of the Sistan region. Today, the area is sparsely populated due to these harsh conditions.

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File:Helmandrivermap.png
Helmandrivermap.png
File:Dust storm in Afghanistan and Pakistan.A2003266.0625.500m.jpg
Dust storm in Afghanistan and...
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