Stepped Spillway as an Energy Dissipater

Abstract

This paper describes an experimental investigation into the hydraulics of ogee-profile stepped spillways, examines their viability as an alternative to smooth-back spillways and investigates their efficiency in reducing the downstream energy and length of the hydraulic jump. Tests were performed in a long rectangular flume with glass walls on both sides. One smooth model was used as a benchmark for comparison with stepped models made out of a combination of crests and bottoms of different step heights. Significant reductions in terminal velocities and total energies were observed, where the stepped spillway profiles tested proved to be very effective in terms of energy dissipation for flows of the order of the design head or lower. For flows beyond the design head, the effectiveness of the stepped spillway configuration was reduced and became negligible for heads greater than one and a half times the design head. It was concluded that the number of steps is the overbearing factor in expending flow kinetic energy and, therefore, reducing the length of the downstream forming hydraulic jump.