kariz wells 坎兒井 in Turpan, China

I took city buses to visit the kariz wells, an underground irrigation channel for water for domestic use built by local people 2000 years ago. The karez is considered as one of the three great ancient projects in china ,other two being the great wall and grand canal. being placed side by side with the dujiangyan irrigation project in sichuan province and the ling canal in guangxi , it is also known as one of the three ancient water conservancy projects in china. The karez is distributed in turpan, kumuk ,sanji , hotan ,atush ,kuqa and urumqi in history, but mainly in turpan and kumul. The karez is a very delicate irrigation system composed of vertical wells , underground canal , open canal and amall ponds or reservoirs , with the main body buried under the ground. the system can be devided into the water accumulation part and the water conveyance part. The underground canals are at a height of 1.5--1.7m and a width of 0.6--0.7m , with total length of 5-20 km. the number of the karez in xinjiang once reached 1784 . with 172367 vertical wells , 5272 km long underground canals and 858 million cubic meter of annual water output.