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United States Department of Agriculture

Agricultural Research Service

RCC Stepped Spillways
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The research here at the lab provides the design guidance necessary to determine RCC stepped spillway design parameters including inception point, flow depth, air entrainment, and energy dissipation. Results show that the normalized clear water flow depth downstream of the inception point is a function of chute slope and the ratio of step height to critical depth, the normalized flow depth upstream of the inception point is a function of chute slope, the ratio of step height to critical depth, and the normalized length from the crest. Two new relationships have been introduced from the RCC research that can be used to determine the flow depth at any location upstream and downstream of the inception point for stepped spillways on embankment dams.


The HERU continues to cooperate with the Natural Resources Conservation Service (NRCS) to improve criteria for utilizing roller compacted concrete (RCC) spillways over existing earth embankments, as to provide adequate spillway capacity for major flood events and to provide overtopping protection  An indoor facility and a state-of-the-art large scale outdoor stepped spillway facility have provided the collection and the expansion of a unique set of data  including air entrainment inception point, air concentrations, flow depth, velocities, and energy dissipation.  Data from specific and generalized model studies have been analyzed, and potential options for containing flow in converging and non-converging spillways have been evaluated. Theoretically complex relationships for converging stepped spillways have been developed along with practical, straight-forward stepped spillway design relationships that can be easily applied in the field.  This research has extended the planned service life of many dams throughout the U.S. while also preserving millions of dollars in annual benefits that these dams provide.





Last Modified: 9/28/2017
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