Submitted to: International Conference on Water Resources Engineering Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/3/1998
Publication Date: N/A
Citation: Interpretive Summary: A new water supply dam is being designed using roller compacted concrete (RCC). This construction technique allows the emergency spillway to be located over the top of the dam, with a stepped surface to decrease the water velocity and energy. A model study was performed to determine the best spillway step size and to determine if converging spillway walls would dstill perform well hydraulically. Two different step sizes were found to d a good job of reducing the energy of the flowing water. Three spillway convergence angles were examined, but converging the spillway from 500 feet wide to 400 feet wide was the recommended shape. Reducing the spillway width provided a cost savings of approximately $2 million by reducing the amount of rock excavation and decreasing the stilling basin size. The model study presents detailed information about the flow velocities and energy losses that can be expected in the spillway and stilling basin. These results should be of interest to public and private dam builders and owners.
Technical Abstract: Roller compacted concrete (RCC) materials and construction techniques are becoming more common for dam construction where foundation conditions are suitable. RCC technology offers the advantage of allowing the emergency spillway to be located over the top of the dam, with a stepped surface to provide some energy dissipation. A model study was performed for a spillway yon Randleman Lake Dam, a proposed RCC dam to be constructed near Randleman NC. A 1:40 scale, two-dimensional model was evaluated to find the optimum step height and to compare stepped surface energy losses with a smooth spillway surface. A 1:40 scale, three-dimensional model was examined to assess spillway and stilling basin performance for spillway wall convergence angles of 0, 20.9, and 32.5 deg. Velocity profiles were collected and analyzed for the different spillway configurations, and these data are presented and discussed. The stepped spillway surface dissipated enough energy to allow the stilling basin length to be reduced. Substantia cost savings were achieved by converging the spillway chute walls, while maintaining acceptable hydraulic performance.