 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 Flaming Mountains.The canals channel the water to the surface, taking advantage of the current provided by the gravity of the downward slope of the Turpan Depression.The canals are mostly underground to reduce water evaporation and to make the slope long enough to reach far distances being only gravity fed.