Submitted to: Journal of Hydraulic Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2016
Publication Date: 5/1/2017
Citation: Hunt, S.L., Kadavy, K.C., Crookston, B.M. 2017. Discussion of "Simple design criterion for residual energy on embankment dam stepped spillways" by Stefan Felder and Hubert Chanson. Journal of Hydraulic Engineering. 143(5):0717001-1-3.
Interpretive Summary: Stepped spillways are one of many embankment dam rehabilitation options for embankment overtopping protection being used worldwide. Researchers at the University of Queensland of New South Wales in Australia and researchers from the USDA-ARS Hydraulic Engineering Research Unit have both conducted research programs in order to develop stepped spillway design guidance for practitioners. While the researchers in Australia provide a simplified approach to estimate energy at stepped spillways, their approach ignores the possibility that other spillway design parameters (i.e. step geometry and chute slope) also impact the amount of energy. This paper presents an in-depth discussion on these design parameters and their influence on the design of stepped spillways.
Technical Abstract: Researchers from the University of Queensland of New South Wales provided guidance to designers regarding the hydraulic performance of embankment dam stepped spillways. Their research compares a number of high-quality physical model data sets from multiple laboratories, emphasizing the variability of observed results between modelers. Yet, their research does not include pertinent research conducted at the USDA-ARS Hydraulic Engineering Research Unit. Additionally, their research commented on the existence of complex hydraulic behaviors that may be difficult to anticipate in practice for these types of spillways. Therefore, the researchers provided a recommendation of using the median value of the residual energy depending on the chute slope coupled with a sensitivity analysis; the researchers also specify mandatory physical modeling for all stepped spillway projects. The discussers of this paper gratefully acknowledge the contributions made by the researchers because the accurate estimation of residual energy of stepped spillways is of great importance. However, there are some important aspects to clarify and highlight. This paper presents a discussion to provide additional information on this matter that is directed specifically to practitioners and includes the air-water flow data from the USDA-ARS Hydraulic Engineering Research Unit. The paper also clarifies key design points, including that residual energy at stepped chutes is influenced by flow regime, step geometry, and chute slope and should not be overlooked.