Canal del Cuello de Botella (Baopingkou)

Baopingkou, the "Bottle-Neck Channel," is the third of the three great engineering works of the Dujiangyan Irrigation System and the final gateway through which the waters of the Min River enter the irrigation network of the Chengdu plain. Cut through the solid rock of Mt. Yulei more than two thousand years ago, it is a narrow, steep-walled channel that controls the flow of water into the inner river and prevents the irrigation system from being overwhelmed in times of flood. For visitors walking through the UNESCO World Heritage site, it is one of the most dramatic points along the route, and the place where the genius of the original engineering is most clearly visible.

According to tradition, the channel was carved by Li Bing, the Qin-dynasty governor of Shu commandery, and his engineers by heating the rock face of Mt. Yulei with fire and then cracking it by pouring cold water over it, a slow and laborious process that allowed them to cut a deep notch through the mountain without iron tools capable of quarrying hard sandstone directly. The result is a narrow, tall channel with nearly vertical rock walls, resembling the neck of a bottle, which gives the work its name. The mound of rock separated from the main mass of the mountain during the carving still stands just downstream and is now known as Lidui, the small hill crowned by Fulong Temple inside Lidui Park.

The role of Baopingkou is to act as a constant, self-regulating valve on the inner river. Because the channel is narrow, only a limited volume of water can pass through it at any moment, and excess water in the inner river is automatically backed up and diverted over the Feishayan spillway, which protects the irrigation network downstream from flooding regardless of how much water is coming down the Min. In the dry season, the channel ensures that the irrigation supply continues to flow at a steady rate, and the geometry of the works as a whole allows the system to balance itself without any gates, moving parts, or human intervention.

Baopingkou is best seen from two points along the walking circuit through the Irrigation System: from the top of Lidui inside Lidui Park, where the channel can be looked down upon directly, and from the cliffside walkways on the opposite bank, where the full height of the carved rock walls is most clearly visible. The water flowing through the channel is fast, cold, and turquoise with suspended mineral flour from the mountains, and the contrast between the calm of the upstream pool and the rush of water through the narrow channel is one of the most memorable sights in the entire Dujiangyan site.