PHYSICAL MODEL STUDY OF A PROPOSED CONVERGING RCC STEPPED SPILLWAY FOR BIG HAYNES CREEK WATERSHED SITE H-3 IN GWINNETT COUNTY, GEORGIA

摘要

The USDA-NRCS has assisted with the design and construction of nearly 11,000 small watershed dams in the U.S., and by 2016, nearly one-third of these structures will reach the end of their planned service life. Time takes a toll on these structures. Some face structural integrity problems while others have sediment filled sediment pools and sedimentation of the flood pools. In some cases, development surrounding the dams has caused a change in hazard classification. Since many of these structures no longer meet federal and state dam safety requirements, the dam safety community has become increasingly aware of their failure potential. For these structures to continue to function properly and safely, rehabilitation is required. If ignored, these dams could place life and property at risk. Big Haynes Creek Watershed Site H-3 in Georgia is one of the dams that was designed and constructed with the assistance of the USDA-NRCS. Since its construction in 1963, the dam has experienced a hazard classification change that requires an increase in spillway capacity. Because of extensive development in the area, a converging roller compacted concrete (RCC) stepped spillway was proposed over the existing dam as a means of providing the needed additional spillway capacity. The Agricultural Research Service (ARS) performed a physical model study of the proposed design using a 1:22-scale model. The study indicated that the use of sloping stepped sidewalls in the converging section of the spillway did not perform well and that smoothing and extending the walls improved overall performance. The extension of the stilling basin end sill up the sloping basin walls also improved the performance. This report documents these findings.