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The Introduction of Karez Well, Xinjiang

Karez Well is a kind of underground water works invented and built by laboring people of various ethnic groups in China to adapt to the natural environment in dry region. In Xinjiang, Karez Wells are mainly in Hami, Turpan and Mori, but they are most in Turpan Basin, where there are altogether 1100-odd Karez wells and have the total length of over 5000 km.
Karez, or kan'erjing in Chinese, is reputed as one of the three major construction projects in ancient China, together with the Great Wall and the Grand Canal. The history of this unique underground irrigation system can be traced back over more than 2,000 years.

The Karez Water System is a unique water system in Xinjiang region which is still in good operable service. Karez is mainly distributed in Turpan, Hami and Helei districts in Xinjiang, where Turpan District is reputed as the place with the most karez (more than 1,000). The annual discharge of karez in Turpan totals 29.4 billion cubic meters, irrigating the vast farmlands in the region all year round. Linked together, the total length of these karez would exceed 5,000 kilometers. Thus, karez is also dubbed the "underground canal". This long-lasting Water System not only solves the drinking water problem of the local people and provides water for wild animals, but it also prevents the Aiding Lake, located in the lowest point of Turpan basin, from drying up and becoming a desert. It also provides a balance for the local fauna, a benefit of economic and zoological value.

The length of the Karez wells varies with the geographical environment. A Karez well generally consists of four parts: the open channel, the underground channel, the vertical well and the small reservoir. The underground channel constitutes the main body of the system, which is in fact the underground watercourse. The vertical well functions as the outlet for the shipping out of mud and gravels. The water outlet of the underground channel is called "dragon mouth", which is in connection with the open channels above ground. The water of the Karez wells empties into the small reservoir before it is drawn into the channels.

karez wells perfectly meet irrigation needs and play a vital role in local agriculture despite the dry and hot climate, large-scale vaporization and occasional sandstorms in windy seasons. In summer, large amounts of snowbroth and rainwater flow into Turpan Basin and infiltrate into the ground, and constitute underground current, thus making an adequate water source under ground for Karez Wells. When a sandstorm breaks out, sometimes the channels of an aboveground irrigation system can get filled up with sand and fail to work. The karez irrigation system, however, is immune to such problems since its channels run underground. Since karez water is primarily thawed snow and melted ice, the stream runs very steadily, and the changes in season do not influence it too much. Meanwhile, the underground system also contributes to a low evaporation rate.

The construction of the Karez Water System was difficult since the project was very large. Its four parts, the drilled shaft, the blind drain, the open drain and the flooded dam, form an integrated system of water storage, irrigation and maintenance. Currently there are still 1100 Karez Water Channels in the Turpan area, which irrigate more than 35 percent of the total land.