Karez Well system is the pride of Turpan. Along with the Great Wall and Grand Beijing-Hangzhou Canal it is regarded as the three most important achievements of ancient China. At its peak, this irrigation system exceeded 5,000 km (3,106 miles) and was also referred to as 'the Underground Great Wall'.
Karez Wells were created by the local people for irrigation and drinking in the past time. Because the desert area is lack of rains all the time and the melt snow water becomes the main water resource of local people, Karaz irrigation system is vital to Turpan. To some extent, there would be no Turpan culture if there were no Karez Well system. Karezes have also been found in Iran, the Sahara, etc., but the ones in Turpan are the most complete.
Xinjiang Province has over 1,600 Karez systems with most of which are in Turpan. There are about 1,200 such systems in Turpan and some 850 of which are still in active use.
A Karez Well is dig with many vertical wells and one underground cannel. The vertical wells are for ventilation, digging and maintenance of the karez. The bottoms of all the vertical wells are connected so that water can pass through. The underground canal is about 2 meters high and covered with earth to resist the heat. The surface canals, connected to the underground ones, are not more than 1 meter wide with trees planted on both sides to prevent evaporation.
Melting snow from the Tianshan Mountain is the water source of the karez wells. Water is collected by vertical wells and conducted by the underground canals to the oasis, where the water is held in the ground canals for irrigation. The vertical wells near the water source may be 100 meters (328 feet) deep while further downstream they are less than 10 meters (32.8 feet) deep.
Turpan is the hottest and driest place in China, Karez reduces evaporation and safe every drip of the previous water. Although big water channels and reservoirs have been built in recent years, Karez Well Systems still play an important role in Turpan.