Flow depth and energy coefficient relationships for stepped spillways

A multi-year, large-scale physical model study of stepped chutes was conducted over a broad range of design parameters (i.e. step heights, slopes, and unit discharges). Air entrainment developed naturally as the flow descended the chute. Air entrainment began to develop downstream of the surface inception point at L/Li = 1.0, and it became fully developed at approximately L/Li = 2.0. Depending on the chute slope, energy loss in the model ranged from 20% near L/Li = 1.0 to as much as 85% near L/Li = 6.0. The contributions of this study are the development of flow depth, clear-water flow depth, and energy coefficient relationships for stepped chutes with slopes ranging from 10 to 30°. Although stepped chutes provide significant energy dissipation, large steps may have an adverse effect on the resulting Froude number; consequently, a longer stilling basin may be required then one might expect. The results of this research are expected to make a significant impact of the design of these structures