Yuzui is a long and narrow dyke built in the center of the Minjiang River, dividing Minjiang into the inner river and the outer. The inner river diverts water into Chengdu Plain through Baopingkou. And the outer is the main flow, which carries off 80% of silt. Feishayan is spillway for releasing flood and silt from inner river to outer river. Baopingkou is the main diversion gate to draw in water for irrigation in shape of bottleneck. In construction of irrigation system, Li Bing had a canal cut through the Yulei Mountain toward Chengdu Plain. Baopingkou marks the inlet of the man-made river. It works for conducting water and controlling the volume of inflowing water. Unbelievably, it still controls the waters of the Minjiang River and distributes it to the fertile farmland of the Chengdu plains. It is a world heritage site because it illustrated ancient China's immense advances in science and technology.