PLT - Hydraulics of beveled face stepped spillways

Rehabilitation of embankment dams has included the usage of RCC to construct stepped spillways. Significant research has been completed on the complex flows and hydraulics of stepped chutes with vertical faces (usage of formworks). However, construction techniques common to RCC often result in steps with an inclined or beveled vertical face. Currently, there is limited scientific understanding on how this step geometry modifies the flow field relative to the conventional square edge, and how any changes would affect the overall hydraulic performance of the stepped spillways. Therefore, this study has been undertaken to better understand the hydraulics of stepped chutes with inclined faces. Research is being conducted in a field-scale sectional facility at Utah Water Research Laboratory with a stepped chute having a mild slope of 3:1 (H:V), width of 1m, and total drop height of 1.83 m. A broad crested weir at the top conveys water to the stepped spillway. Tests were conducted for a step height of 0.2 m with the vertical faces sloping at 45 degrees. Air water flow properties were obtained using a dual tip phase detection conductivity probe. A critical component of this research includes a baseline study of steps with vertical faces, for direct comparison. Results showed that the length from the crest to the point of inception was reduced by approximately (20-25) % with the use of beveled face steps. Beveled faces also increase the extent of splash and spray as well as the required sidewall heights, when compared to the conventional flat steps. Likewise, the mean air concentration was higher for beveled steps, meaning they induced more air entrainment into the flow. For similar distances from the weir crest, it was seen that the interfacial velocity of the multiphase mixture was lower for the beveled face steps and hence slightly lower residual energy. It is anticipated that the results from this study will be of high interest to hydraulic engineers in dam safety.