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Photo: Roller compacted concrete stepped spillway.
ARS hydraulic engineers are helping the Natural Resources Conservation Service rehabilitate aging small dams across the country by increasing their utility and safety with roller compacted concrete stepped spillways. Photo courtesy of NRCS.

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New Designs for Making Old Dams Safer

By Don Comis
June 26, 2009

A group of Agricultural Research Service (ARS) hydraulic engineers are helping to rehabilitate aging small dams across the country.

Efforts are underway to upgrade existing auxiliary spillways or build new spillways for these dams, especially in Oklahoma. These upgraded or new spillways meet current dam safety standards and will increase the useful lives of the dams.

The U.S. Department of Agriculture's Natural Resources Conservation Service (NRCS) has helped build more than 11,000 earthen dams over the years as part of its Watershed Protection and Flood Prevention Operations Program. These dams serve many purposes, but the primary purpose is flood control. Since the program began in 1944, ARS Hydraulic Engineering Research Unit (HERU) engineers in Stillwater, Okla., have partnered with NRCS in the development of design standards for the dams.

When ARS hydraulic engineer Sherry L. Hunt and her colleagues were asked recently by NRCS to help evaluate and design retrofitted Roller Compacted Concrete (RCC) stepped spillways for dams in Georgia and North Dakota, they found the same technology also can help increase flow capacity on many of these dams across the country. So they developed generalized criteria for designs that could be used anywhere in the country.

Compacting concrete with a roller is a fast way to make a tough surface.

With the many changes that have occurred over the years—including deterioration, changes in upstream and downstream land use and population, and changes in dam safety laws—the research by the HERU engineers with this technology is once again helping NRCS, which has the lead for design and construction of these earthen dams.

The ARS engineers conduct model studies both indoors at small scales and also outdoors at large scales. This summer Hunt will begin using a large-scale flume outdoors that is the actual size of the RCC spillways being designed for these dams. ARS engineers will use the data from the water flow on their experimental spillways to develop design and construction guidelines.

ARS is the principal intramural scientific research agency in USDA.