Abstract: Steps on the overflow surface of stepped spillway is widely used in engineering practice as the steps enlarges the roughness of overflow surface, which brings about prominent energy dissipation effect and good aeration effect. However, due to the special shape of shrinking chute and various combinations of steps and sink sizes, the variation of water flow in the shrinking chute is more complicated, resulting in some difficulty in the hydraulic study of such structure. Under the background of actual engineering demand, an improved coefficient method is put forward in this paper according to Chanson’s formula and the measurement results of existing model test. The calculated water depth of each section in tapered chute of stepped spillway obtained by the proposed method is in good agreement with that of corresponding section measured by model test. The relative error between the calculated water depth and the measured water depth is less than 5%. The method is proved to be of high accuracy and can be used to calculate the water depth in shrinking chute of stepped spillways. The research finding offers a scientific basis for improving the hydraulic characteristics of tapered chute of stepped spillways, and is of guiding significance for engineering applications.

Key words: stepped spillway, tapered chute, water depth calculation, hydraulic characteristics, Chanson’s method, model test