The karez system in Turpan Basin. (PHOTO: VCG)

By BI Weizi

The famous karez system, a vertical tunnel irrigation system in desert areas, is known as one of the three great projects of ancient China, along with the Great Wall and the Beijing -Hangzhou Grand Canal. It is commonly found in Turpan Basin, Xinjiang Uygur Autonomous Region.

The word karez means "well" in local Uygur language. Turpan karez system was essential to development of Turpan as a significant oasis transit point on the ancient Silk Road around the barren and harsh Taklamakan Desert.

The large number of karez in the Turpan Basin have long become part of the natural geography. Turpan is one of the most arid regions in China, with as little as 16 mm of annual precipitation and as much as 3,000 mm of evaporation, making it the "dry pole" of China. However, with Turpan karez system, water can be delivered through underground canals without being affected by the seasons or sand, making all-year-round irrigation possible.

A complete Turpan karez system consists of four parts: vertical wells, underground water canals, surface channels and dams. First, a number of wells are drilled vertically to collect rainwater, glacier and snow melted water that seeps into the ground during spring and summer time; then, the water is diverted through underground canals to its destination before being brought to surface channels for production and irrigation, which ensures that it will not evaporate or be polluted by the heat and gusty winds; finally, a dam pools water for human use and controls the amount of water flow.

Karez system has witnessed the prosperity and development of Turpan Basin and is a milestone in the history of oasis agriculture development in arid zones.