The Dujiangyan Irrigation System [都江堰]

The irrigation system consists of three sections: the Fish Mouth [鱼嘴], which splits the Min River into the inner and outer rivers, the Feisha Dike [飞沙堰], which helps reduce the amount of slit carried by the inner Min River [内江] before it flows into the Baopingkou ("mouth of the treasure bottle") Aqueduct [宝瓶口], the third section which leads the waters into the Chengdu Plain. The bed of the outer river is convex while that of the inner river is concave. This fact, an integral part of Li Bing's original design, results in less slit going into the inner river which is primarily used for irrigation.

The Feisha Dike is situated at the point where the inner Min River makes its first turn after split from the outer Min River at the Fish Mouth. Li Bing and his people cleverly used the fact that the waters flow at different speeds at the river turn, with the outer ring moving slowly and thus carrying most of the slit, which is then filtered at the dike and goes back into the outer Min River (which eventually merges into the Yangtze River). The dike also adjusts the capacity of the inner river for irrigation such that it carries 40% of the water capacity in the entire Min River in a flood season while 60% of the capacity in a drought season.

The Fish Mouth is a passage cut through the Yulei Mountain [玉垒山]. Before the invention of explosives, the builders accomplished this by repeatedly heating the rock with wood fires and cooling the rock with the water from the river below to crack and weaken it. The strenuous work lasted seven years before the mountain finally yielded the openning.