It makes the method of reckoning curve of water surface simple to calculate critical and normal water depth by using the alternative method

and then calculate average water depth according to the method. The flow length between the site which water depth equal to the average water depth and the head of steep section is calculated by average water depth. By this

the side wall of steep section of spillway from the head of steep section to the site of average water depth is designed as the height of water depth of head of section adding safety height.The side wall of flow below average water depth is designed as the height of average water adding safety height.This makes the construction convenient and cost smallest. These provided a scientific basis for design

construction and budget cost of side wall of spillway steep section.