Dujiangyan Irrigation System

     China lies in the North Temperate Zone, with a changeable climate and a complex topography. As droughts and floods were frequent, water control projects were built in ancient China to tackle the disasters. The projects included canals, ponds, dikes, and underground ditches. The most important irrigation systems among them were canals in plain regions and ponds in hilly areas. There were a number of ancient irrigation systems in Shaanxi, Hebei, Sichuan, Beijing and Ningxia. The most famous among them is the Dujiangyan irrigation system in Sichuan, which is still playing an important role in local agricultural production.

    Dujiangyan, or Dujiang Weir, previously known as Jin Di (Golden Weir) or the Great Weir of Du'an, was built in the 3rd century BC. It got the name of Dujiangyan in the Song Dynasty. The project is located in Guanxian county on the middle reaches of the Minjiang River. Flowing from high mountains and valleys, the river enters the Chendu Plain and slows down, where large amounts of sand and dirt silt up the riverbed. Flooding was quite frequent. In his later years, King Zhaowang (306 BC-251 BC) of the Qin State appointed Li Bing, a noted water resources expert, to be governor of Shu (Sichuan). Right after assuming the post Li Bing began presiding over this water control project. The irrigation system consists of three parts: Yuzui, Baopingkou, and Feishayan. Li first had the builders cut Baopingkou, an opening in the eastern bank of the Minjiang, intending to divert water to the fields in the Chengdu Plain.

    However, due to the high terrain water could not flow through the opening. He then asked the builders to build a structure in the shape of a fish mouth (yuzui) in the middle of the river with stones filled in bamboo cages, which helps to distribute water to the east bank. This structure divides the river into two channels: waijiang, the outer main channel which accommodates flood water, and neijiang, the inner channel which diverts water for irrigation.

    Baopingkou, the opening in the east bank between Yuleishan and Lidui, controls the flow from the inner channel to the irrigation canal. Cutting the opening took great efforts as the rocks there were very hard. The workers first set fires on the rocks to heat them, and then poured cold water or vinegar on them so that they would crack. Inch by inch they managed to cut a passage that is 20 meters wide, 40 meters deep and 80 meters long. Feishayan, or the spillway weir, was built between yuzui and baopingkou. In flooding season flood water will flow over this weir from the inner channel to the outer channel, carrying lots of silt and cobbles thus reducing sediments in the canal. As Dujiangyan is situated at the highest place of the Chengdu Plain, an alluvial plain that fans out in the Sichuan Basin, the natural flow from the irrigation system reaches large areas of farmland, turning the Chengdu Plain into "a land of abundance."

    After more than 2200 years, Dujiangyan is still functioning excellently as a flood control and irrigation project, and it has also become a well-known tourist destination. As a representative of ancient engineering in water control, Dujiangyan has been inscribed on the UNESCO World Heritage List.