The Karez---the World’s Largest and Most Complicated Underground Irrigation Project

　　The Karez, invented in the Western Han Dynasty, has used as underground irrigation system for more than 2000 years. It is a great invention of the working people in China to adapt to dry climate with high evaporation and low rainfall.

　　The main design principle of the Karez is to transport water through an artificial underground channel from the aquifer to the above-ground channel for irrigation. The project is composed of four parts: vertical access shafts, an underground channel, an above-ground channel and a dam. Water in the aquifer mainly comes from melted snow that infiltrates into the ground. People would first find an aquifer and design a route to distribute water. Then a number of access shafts shall be built and connected by underground channels. The water flow makes full use of the natural slope or gravity to reach the irrigation area. This kind of irrigation system reduces the evaporation loss along the way to the greatest extent. At the time of no GPS and only simple laboring tools being applied, it is indeed a great pioneering work that accomplished the goal totally relied on manual for underground operation.

　　Today, in Xinjiang region of China, more than 1700 Karez are still functioning, with an irrigation area of about 500000 mu, most of which are concentrated in Turpan Area.

　　Karez is known as one of the three marvelous engineering of ancient China  with no parallel except the Great Wall and the Grand Canal.