Submitted to: Workshop Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/13/2014
Publication Date: 6/25/2014
Citation: Hunt, S.L., Kadavy, K.C. 2014. Flow depth and energy coefficient relatiohnships for stepped spillways. In: Hubert Chanson and Luke Toombes, Hydraulic structures and society - Engineering challenges and extremes. 5th IAHR International Symposium on Hydraulic Structures, June 25-27, 2014, Brisbane, Australia. p. 1-9.
Interpretive Summary: Stepped spillways are often used to upgrade aging embankment dams, but design tools have been limited for application of these structures until recently. The United States Department of Agriculture (USDA)-Agricultural Research Service (ARS) has conducted a multi-year study to develop design equations for stepped spillways. Design equations for flow depth and an energy parameter were developed to aid in the design of spillway walls and the downstream energy dissipation basin. These equations provide advancements in practical design guidance for the training walls and energy dissipation basins of the stepped chutes applied to new and aging embankment dams.
Technical Abstract: 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.