Scour downstream of hydraulic structures, particularly piano key weirs (PKWs), is a critical issue impacting the stability of these structures. PKWs have gained attention over the past two decades due to their increased discharge coefficient and economic design. However, accurate prediction of erosion is essential for their effective use. This study was conducted using dimensional analysis and extensive laboratory experiments at the Hydraulic Laboratory of Tarbiat Modares University in Tehran. The parameters influencing erosion were examined. The research aimed to investigate the impact of weir geometric characteristics (changes in the slope of the outlet keys), inlet flow discharge, tailwater level, size of non-cohesive sediment particles, and flow drop height on the characteristics of the scour hole and changes in the downstream bed topography of type A piano key weir (with and without energy-dissipating structures and bed protection). The results showed that the maximum scour depth increases with the Froude number of particles and flow drop height. Installing baffles on the outlet keys increased the dissipated energy by an average of 22% and reduced erosion by an average of 15%. The location of the maximum erosion depth occurred farther from the weir toe, resulting in a 31% reduction in the area and volume of the scour hole compared to a weir without baffles. The length of the apron also effectively reduced the volume of the scour hole. Using numerical modeling with Flow-3D software to simulate the flow pattern and scour downstream of trapezoidal type A, B, C, and D weirs, the model accurately simulated the scour pattern and flow profile passing through the piano key weir. The study of the influence of geometry and different weir models showed that the weir geometry and the presence or absence of upstream and downstream aprons affect the distribution of three-dimensional velocities and flow patterns. In the type C weir model, the flow velocity impacting the tailw