Scour evolution for steady and unsteady flow conditions downstream of Type A piano key weirs

Abstract For the first time a comprehensive analysis for steady and unsteady flow conditions was performed of timedependent scour processes in non-cohesive sediment downstream of a Type A piano key weir. The evolution and progression of scour of large-scale laboratory experiments were interpreted using an empirical approach and adapting a theoretical model based on the phenomenological theory of turbulence developed elsewhere. The results were within 30% of experimental with the R-squared values of 0.972 for the theoretical model and 0.993 for a calibrated empirical model. Results of this study demonstrate consistent scour evolution kinetics between steady and unsteady flow cases, although in the latter, the maximum scour features were smaller than their steady-state counterparts. This study highlights the novelty of integrating experimental and theoretical frameworks to validate and enhance the design of complex hydraulic structures. Quantitative findings confirm the robustness of first principles-based approaches, offering practical insights and design parameters critical for addressing scour challenges in non-cohesive sediment environments.