Transition Stretch of Spillways with Bevelled Steps

In stepped spillways design it is necessary to define the transition section between the crest and the constant slope stretch. The transition stretch design becomes more challenging when are adopted greater steps in the downstream stretch. Care to ensure an adequate flow behavior in this stretch is especially relevant for low discharges per unit width. An experimental study was developed using a 1:5 scale physical model in order to contribute in transition stretch design. It was possible to determine the transition stretch of spillway with the least possible number of steps and minimize the intensity of jumps from the steps. The study was carried out considering a typical channel slope of 1V:0.75H consisting of steps with nominal heights of 0.90 m and 1.80 m, subject to discharges per unit width between 0.2 m³.s^-1.m^-1 and 2.0 m³.s^-1.m^-1. Steps were configured with 4 cm side bevels to consider a solution adopted in prototypes where constructive difficulty prevents the adoption of steps with sharp edge. The transition section of a stepped spillway with best hydraulic behavior resulted in five steps with heights gradually variable up to 0.45 m. The results obtained allowed to determine a procedure to calculate the discharge per unit width from which there is no risk of jumps along the transition stretch.