Onset of skimming flow on stepped spillways

Assuming that skimming flow occurs when the jet leaving a step has a slope equal to that of the stepped spillway when it impinges on the pool behind it on the next step, an equation has been developed to predict the incipient value of y(c)/h, where y(c) = critical depth and h = step height. This equation was found to agree well with most of the experimental observations for h/l greater than about 1.0, where I = step length. For h/l = 1.7, the incipient value of y(c)/h = 0.24, whereas for values of h/l smaller than about 0.8, y(c)/h is almost constant at 0.8.