ENERGY-DISSIPATION ON STEPPED SPILLWAYS

Potentially high energy dissipation on stepped overflow spillways would imply a significant reduction of the size of downstream stilling basins. The amount of energy loss on such spillways under skimming-flow conditions is examined experimentally for structures with a moderate number of steps and a width-to-height ratio equal to 0.7. The experimental results, supported by dimensional considerations, indicate that the most important parameters governing energy dissipation are the ratio of the critical depth of flow passing over the spillway to the step height y(c)/h, and the number of steps N. Dissipation is highest for the small values of y(c)/h tested, near unity, and decreases with increasing y(c)/h; for a certain y(c)/h the dissipation increases with N. The results are compared to those of earlier investigations referring to a large number of steps. For commonly used ranges of the step dimensions, a general relation is established between the energy loss and the parameter y(c)/h, which may be useful in practical applications.