Abstract: Stepped spillways have gained significant interest and popularity among researchers. Energy dissipation rate and Froude number are important hydraulic parameters. In this paper we introduce the concept of relative Froude number of stepped spillway which reflects the effect of step on the value of Froude number through comparing the Froude number of stepped spillway and the corresponding Froude number of smooth spillway. Through tests on stepped spillways (with different step heights 0.5m, 1.0m, 2.0m and chute angle 38.66°), we investigate the relation between relative Froude number and relative rate of energy dissipation. Results show that in non-uniform flow the relative Froude number is in linear relation with relative rate of energy dissipation, and the correlation coefficient is 0.9927-0.9989. Further study shows that the slope of the linear relation increases with the increase of unit width discharge, but the height of step has only slight effect on the slope of the linear relation between relative Froude number and relative ratio of energy dissipation.

Key words: stepped spillway, relative energy dissipation ratio, relative Froude number, non-uniform flow, linear relation