Hydraulics of skimming flows over stepped channels and spillways

Stepped channel applications include a broad range of domains. A detailed review (past and present) was published by the author (Chanson 1995). To date most studies on gepped chutes applies to gradually variedflows in rectangular prismatic channels with horizontal. The three-dimensional features of stepped chute flows are not accounted. Regarding dimensional analysis, several dimensionless numbers must be taken into account for the hydraulic study of skimming flows past stepped chutes. The Froude number takes into account tk gravity effects with free-surface flows while the Reynolds number is a characteristic of the form (drag) resistance. In presence of free-surface aeration, surface tension effects must also be taken into account. Overall, a true similitude is not possible. Neglecting the air entrainment effects (Chanson 1994b), the detailed investigation of the author showed explicitly that, for the analysed set of data: 1. The Froude number has no effect on the flow resistance. 2. The skin drag has little effect on the flow resistance for steep slopes. For flat stepped chutes, the skin friction might have some effect (as suggested in Chanson 1994b). But additional data is required to verify or deny this point. 3. The Reynolds number has no effect on the flow resistance, for these supercritical extremely turbulent flows. The author does not believe that the conclusion of his analysis is the "final word" on the topic. New experiments, in particular on prototypes, might confirm or not the analysis.