Turfan water system



The Turfan water system (locally called karez water system) in Turfan, located in the Turfan Depression, Xinjiang, China, is a  well water collection system that has been listed as one of the three greatest water projects of ancient China together with the Du Jiang Yan Irrigation System, and the Grand Canal. The karezes are an important invention by the Turpan people. The word karez means  "well" in the local Uyghur language. Turfan has the Turfan Water Museum (a Protected Area of the People's Republic of China) dedicated to demonstrating its karez water system, as well as exhibiting other historical artifacts. Turfan's well system was crucial in Turfan's development as an important oasis stopover on the ancient Silk Route skirting the barren and hostile Taklamakan Desert. Turfan owes its prosperity to the water provided by its karez well system.

Description
Turpan's karez water system is made up of a horizontal series of vertically dug wells that are then linked  by underground water canals to   collect  water from the  watershed surface runoff from the base of the Tian Shan Mountains and the nearby  the Flaming Mountains, then  channels the water to the surface, taking advantage of the current provided by the gravity of the downward slope of the Turfan Depression. The canals are mostly underground to reduce water evaporation.

The system has  wells, dams and underground canals built to store the water and control the amount of water flow. Vertical wells are dug at various points to tap into the water current flowing down sloping land from the source, mountain runoff. The water is then channeled through underground canals dug from the bottom of one well to the next well and then to the desired destination, Turfan's irrigation system. This irrigation system of special connected wells originated during the Han Dynasty (206 BC – 24 AD). In Xinjiang, the greatest number of karez wells are in the Turfan Depression, where today there remain over 1100 karez wells and channels having a total length of over 5000 kilometers. The local geography makes karez wells practical for agricultural irrigation and other uses. Turfan is located in the second deepest geographical depression in the world, with over 4,000 square kilometers of land below sea level and with soil that forms a sturdy basin. Water naturally flows down from the nearby mountains during the rainy season in an underground current to the low depression basin under the desert. The Turfan summer is very hot and dry with periods of wind and blowing sand. The water from the underground channels provides a stable water source year round, independent of season.

Importance
Ample water was extremely important to Turfan so the oasis city could service the many caravans on the Silk Route stopping there for rest and recuperation before taking, or after returning from,  a route  skirting the Taklamakan Desert. The caravans included not only merchant traders and missionaries with their armed escorts (to stave off bandits), but animals including camels, sometimes numbering into the thousands, along with camel drivers, agents and other assorted personnel, all of whom might stay for a week or more. The caravans needed pastures for their animals, resting facilities, trading bazaars for conducting business, as well as ample  supplies of food and water that could be bought to replenish their supplies.