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Overtopping Embankment Protection Systems
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Roller Compacted Concrete (RCC) Stepped Spillways
-Developing engineering design tools for dam safety

The Congressional passage of the Flood Control Acts of the 1940’s and 1950’s authorized the USDA-Natural Resources Conservation Service to provide technical and financial assistance for the construction of nearly 12,000 flood control dams. The majority of the dams were constructed with a 50year planned service life to protect agricultural land from flooding. With the peak of construction in 1962, many of these dams have surpassed the end of their planned service life. In addition, many dams present challenges today, including deterioration of structural component, sediment deposition in flood storage pools, more extreme weather events, land use changes, and population changes in the vicinity of the dam. To address these challenges, scientists at the USDA-ARS Hydraulic Engineering Research Unit are developing design guidance for embankment overtopping protection systems, specifically roller compacted concrete (RCC) stepped spillways.

Research has led to the development of generalized design guidelines related to the depth, velocity and air concentration of the flow in the chute section and required training wall heights necessary to contain the non-air entrained and air entrained flow within the spillway. The design criteria developed for embankment dams accounts for step height, spillway chute slope and flow discharge. Today, scientists are conducting research on unique design features (i.e. convergence – narrowing of the spillway from the crest to the outlet) of the stepped spillway chute and the hydraulics of the stilling basin associated with stepped spillways. For testing and proper evaluation of air-entrained flow, scientists constructed an outdoor, large scale, state-of the art, stepped spillway facility. An indoor model facility is utilized for conducting research on the three-dimensional aspect of more unique designs.

The impact of this research has led to stepped spillway construction for the means of providing embankment overtopping protection. To date, the design criteria developed by ARS scientists has been implemented in stepped spillway designs in Texas, Oklahoma, Georgia, West Virginia, Pennsylvania, New Mexico, Kentucky, among others. It is likely stepped spillway design criteria developed by ARS scientists have been executed worldwide with requests for journal publications made by international engineering communities.
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Stepped Spillway Facility


Converging Stepped Spillway Model

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USDA-ARS Stepped Chute Design Criteria