It was not easy to hold steady the fill material on the slippery riverbed formed with artificial concrete during the river close-off on the diversion channel. And it was even more difficult than that on the main channel since the inflow of 10300 m 3 /s, the water fall of 4 meters, and water running speed of 7 m/s were bigger. The constructors applied steel-framed rock cages and alloy steel nets to roughen the bottom and to increase the friction of the riverbed, so that rock barrier was formed to reduce the difficulty of close-off and to ensure the stability of the fill materials. Two parallel levees were built to take the water fall of the diversion channel, the upstream