The Xinjiang Qanat System of the Turpan Oasis

The Xinjiang Qanat System is a remarkable feat of irrigation engineering skill, and it is considered one of the three great wonders of China, after the Han Dynasty (206 BCE–220 CE) Great Wall and the Sui Dynasty (581–618 CE) Beijing-Hangzhou Grand Canal. The qanat (also known as a karez) system is a rich water source for the Turpan Oasis, tapping groundwater stored in the deep subsurface gravel layers of the Gobi belt. What makes this all the more interesting is the fact that scholars are still not agreed upon when the qanat system was built... and that begs the question of who built it. Climate of the Turpan The Turfan (or Turpan) basin, located to the east of the more famous Tarim Basin, is one of the driest areas in China, with a total precipitation of 15-25 millimeters (under one inch) per year, and an elevation about 160 meters (524 feet) below sea level. The average temperature of the basin is 32.7 degrees Celsius (90.8 degrees Fahrenheit) in July, but the winters are rather chilly, and in January the average temperatures are about 9.5 degrees C (49.6 degrees F), and can fall as low as -28 degrees C (18 degrees F). The Turfan Basis, while a desert, is much more hospitable than its southern neighbor, the harsh Taklamakan Desert. Wedged between the Taklamakan and the Tianshan Mountains, the Turfan was a much preferred, not to say feasible, route for travelers on the Silk Road: its oasis was a critical stopover. Irrigating the Turfan Theres no doubt that the oasis had a natural beginning. A total of 4,000 sq km (1,500 sq mi) of the Turfan Basin lies below sea level; the Turpan Oasis lies in the lowest part, at an elevation of 154 m (505 ft) below average sea level. The oasis is nestled at the foot of the Tianshan (Flaming or Heavenly) mountains, and from autumn to spring, water from snowmelt off the Tienshan rushes into Turpan, revitalizing the oasis naturally. But at some time in its past—scholars argue that occurred anywhere from 200 to 2,000 years ago—the residents of Turpan built a massive qanat system that reached into the water table and tapped the aquifer, in some cases up to 200 m (650 ft) below the surface. That system included over 5,000 km (3,100 mi) of underground tunnels and thousands of wells. Whether it was built as a result of an environmental disaster or merely insurance against one, the Xinjiang qanat system is evidence that the Turpan was a highly prized stop on the Silk Road. Qanats in the Deserts A qanat is a system of underground tunnels and wells that tap deeply buried aquifers in arid and semi-arid places. In brief, a well is dug into the aquifer, a horizontal tunnel is excavated from the well to a surface collection place and ventilation shafts are placed at intervals along the tunnel to provide maintenance access. Invented by the Persians in the 7th century BCE, qanat technology was spread by imperialism: outside of Persia by the 6th century BCE Achaemenid king Darius the Great; into Syria and Jordan by the Romans in the first and second century CE; into North Africa and Spain by the Islamic civilization in the 12th and 13th centuries CE; and finally into North and South America during the 16th century Spanish conquest. The only place in China where qanats exist at all is in Xinjiang Uyghur Autonomous Region, in the Turfan basin on the far western edge of Chinas realm. Deserts make up 43 percent of Xinjiang province, oases only about 4.3 percent and the rest is mountains. In the 2nd century BCE, the international trade network called the Silk Road was dependent on a line of strategically situated oases wedged between the Tianshan Mountains and the Taklamakan Desert in the Tarim and Turfan basins. Turpan was an important oasis in the eastern-most segment of the Silk Road, and, even today, more than 95 percent of the total population and almost all the agriculture, settlements and industries in Xinjiang are concentrated in the Turpan Oasis. The Size and Complexity of the Turpan Qanat System The Turpan qanat system includes at least 1,039 qanats (some sources suggest as many as 1,700), with underground channels stretching for a length of more than 5,000 kilometers, or about 3,100 miles. While there is no doubt that the origins of the Turpan Oasis were natural, there is also no doubt that the Xinjiang Qanat System was built to increase the available access to water. Whether the qanats were built as a result of climate change or to support a population increase or even provide year-round water is open to debate: probably a little of all those things. Estimates for the construction date of the qanats vary from the first century BCE to the 19th century CE. The system is so successful that grapes are grown in a region of what is essentially a continental desert—the earliest grapes in Turpan are from the Subeixi culture Yanghai tombs, with an  AMS radiocarbon date of about 300 BCE. What we know for sure is that in the 1950s, an intense increase in well irrigation was established in Turpan, over-exploiting the aquifer: since then the majority of the qanats have dried and become abandoned. Only 238 were functioning in 2009. The Karez Wells in Turpan were inscribed into UNESCOs Tentative List of World Heritage Sites in 2012. Sources Beck U, Wagner M, Li X, Durkin-Meisterernst D, and Tarasov PE. 2014. 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