Hydraulic Performance Evaluation of RCC Stepped Spillways with Sloped Converging Training Walls

Abstract

More than 5,500 small watershed dams designed and built with support from the USDA Natural Resources Conservation Service (NRCS) will reach the end of their 50 year planned service life by 2018. Changes in watershed hydrology and hazard classification due to urbanization often require these structures to pass greater flows than were originally intended. Roller compacted concrete (RCC) stepped spillways provide an effective solution to this problem. Increased flow requirements, urban constraints, and valley geometry call for convergent chute sections designed with sloped training walls. There are currently no generalized guidelines for convergent sloped training walls. A three-dimensional, physical model study was utilized to conduct an investigation of sloped training wall convergence on 3:1 stepped spillway chutes including flow patterns and run-up for both stepped and smooth sloped training walls. Generalized relationships for stepped and smooth sloped training wall dimensions on a 3:1 RCC stepped spillway chute were developed. Results are expected to assist in the development of general design guidelines for stepped spillways.