 The Baopingkou or Bottle-Neck Channel, which Li Bing gouged through the mountain, is the final part of the system.The channel distributes the water to the farmlands in the Chengdu Plain, whilst the narrow entrance, that gives it its name, works as a check gate, creating the whirlpool flow that carries away the excess water over Flying Sand Fence, to ensure against flooding.Anlan or Couple's Bridge spans the full width of the river connecting the artificial island to both banks and is known as one of the "Five Ancient Bridges of China".