Well system is the pride of Turpan. It along with the Great
Wall and Grand Beijing-Hangzhou Canal is regarded as the three
most important achievements of ancient time.
Karez Wells created by the local people with their wit, dedication, blood and sweat crisscross the Turpan Depression like the vital and complicate blood vessel network. They created it out of necessity. Karaz irrigation system is vital to Turpan. It leads water to the most arid area and has created the vast oasis.
Xinjiang Province has over 1,600 Karez such systems with most of which are in Turpan. There are about 1,200 such systems in Turpan, some 850 of which are in active use.
Keraz systems are very elaborate irrigation systems. It make up of vertical wells, underground ditches, ground ditches and small reservoirs. The depth of the vertical wells and the space between them depends on their distance to the water source. Generally speaking, the ones in the upriver are deeper and more spaced than that in the lower reaches. Space between each vertical well in the up reaches ranges from 30 to 70 meters while in lower reaches it is about 10 to 20 meters. The deepest vertical well is over 90 meters. Karez Well system is usually 3 to 8 kilometers long with the longest one measuring up to 20 kilometers. The vertical wells are for ventilation and maintenance of the Karez. The underground ditches are connected with the surface ones to lead the water up to the ground.
Turpan's unique geographical and climate features explain that
why Karez is built in Turpan in large numbers. Melted snow from
the Tianshan Mountain is the water source of the Karez. During
summer seasons, large amount of melted snow and rain water flow
to the basin. But it quickly seeps into the ground and become
underground streams due to the arid earth surface. Turpan is the
hottest and driest place in China, Karez reduces evaporation and
safe every drip of the previous water.
Karez Well system has a long history of over 2,000 years and it first appeared in the Han Dynasty. Although big water channels and reservoirs have been built in recent years, Karez Well Systems still play an important role in Turpan.