RCC Stepped Spillway Model Study Training Wall Comparison

A problem for many small earthen dams is inadequate spillway capacity. Roller compacted concrete (RCC) stepped spillways have proven to be a viable rehabilitation solution for increasing spillway capacity of these structures. In some cases the RCC stepped spillway is placed in a section of the earthen embankment, with converging chute training walls conforming to the downstream valley. Converging spillways require special consideration in design because the convergence of the spillway causes a shock wave to occur in the flow along the training walls. The shockwave results in an increase in training wall dimensions required. Recent model studies have been reported on required vertical training wall dimensions but little information exists for sloped converging chute training walls. A recent study on converging stepped spillways with sloped training walls has been conducted and is reported in this paper. The study was conducted at the USDA- Agricultural Research Service (ARS) Hydraulic Engineering Research Unit (HERU) in Stillwater, Oklahoma. The study utilized a three-dimensional small scale physical model with a representative spillway having a slope of 3(H):1(V) and training walls of slope ranging from 1:1 to 3:1. Both smooth and stepped training walls were tested in this study. Flow information and water surface profiles were collected and examined for each of the modeled configurations. Run-up along the walls is a controlling factor for determining wall dimensions of this type of structure. Run-up height for smooth training walls was determined to be a function of shockwave height due to convergence. Results are reported in this paper and are compared to previous work on converging vertical training walls. This research is expected to help in the development of design guidelines for similarly designed structures. 14 pp., 1 table, 16 figures, 18 references.