The ancient Karez system is comprised of a series of wells and linking underground channels that uses gravity to bring ground water to the surface, usually far from the source. In Turpan county there are more than 470 systems, totaling over 1,600 kilometers (1, 000 miles) of tunnels. It is considered as one of the three great projects in China with the other two being the Great Wall and the Grand Canal.
Originally ancient oasis towns depend on the streams and rivers nearby into which glaciers in far-off mountains feed. As the glaciers gradually shrank over the centuries, the streams they fed likewise diminished, resulting in less or water flowing to the oasis towns. Then people ingeniously created the karez to draw the underground water to irrigate the farmland. Wells begin at the base of the mountains along the contours of the hillside. To keep the underground channels unclogged, two men and a draught animal work as a team - one man is lowed down to clear the tunnel and buckets of mud are hoisted to the surface by the animal. The tunnels slope less than the contours of the geographical depression, so that the water reaches the oasis close to ground level. The water in karez will not evaporate in large quantities even under the scorching heat and fierce wind, hence ensuring a stable water flow and gravity irrigation.
The Karez system, an irrigation system of wells connected by underground channels, is considered as one of the three great ancient projects in China, the other two being the Great Wall and Great Canal. There are, in the Turpan area, nearly one thousand Karez totaling five thousand kilometers in length.
The structure of the Karez basically consists of wells, underground channels, ground canals and small reservoirs. In spring and summer, a great amount of melting snow and rainfall flow down from the Bogda and Karawuquntag mountains north and west of the Turpan depression into the valleys and then seep into the Gobi Desert.
Taking advantage of the mountain slopes, the working people ingeniously created the Karez to draw the underground water to irrigate the farmland. The water in the Karez will not evaporate in large quantities even under the scorching heat and fierce wind, hence ensuring a stable water flow and gravity irrigation.

The history of Karez can be traced back to the Han dynasty. Recorded in the "Records of Historian" - a chronological historical book written by Sima Qian, the great Han dynasty historian known for his realistic records of historical events, it was called "Well Canals". Most of today's karezes in the Turpan were built in the Qing dynasty and in after years. Nowadays, large stretches of fertile land are still irrigated by karezes. The Wudaolin karez and the karez in the Wuxing Town are open to visitors.