Numerical investigation of skimming flow characteristics over non-uniform gabion-stepped spillways

Abstract

Stepped spillways can be defined as human-made hydraulic structures constructed to monitor and control flow release and attain high energy dissipation. Such spillways are commonly used in embankment dams; however, it is important that a sufficient chute length is provided to develop the required aerated flow; the point at which this occurs is known as the inception point. This paper focusses on the influence of the non-uniform geometry of gabion-stepped spillways (GSS) on the inception point. A numerical investigation using the Reynolds-averaged Navier Stokes (RANS) approach with the software NEWFLUME was adopted to examine the flow over the GSS. The inception point location suggested by the numerical models was compared to the location predicated in the existing formulae available in the literature. The data from the model was then used to generate two novel empirical equations. The equations were based on nonlinear multiple regression (NMR) and evolutionary polynomial regression (EPR) approaches to deliver improved results for non-uniform gabion-stepped spillways. The developed EPR correlation, respectively, scored R2 (determination coefficient) and MAE (mean absolute error) values of 0.93 and 1.66 for the training data and 0.83 and 2.7 for the testing data. In the NMR approach, a reduced R2 value of 0.91 was obtained. The outcomes of this study revealed that the numerical model proposed was able to capture the flow characteristics over the GSS accurately. Additionally, the empirical equations developed in the current investigation yielded better predictions of the inception point location compared to the existing equations. Consequently, the findings of this study can be used to improve the future design of GSS.