Numerical Study of the Effect of Apron Geometry on Downstream Scouring

The contrast in bed roughness versus apron roughness has, until recently, received insufficient attention, despite its significant role in causing downstream scouring. In this study, a validated numerical model has employed to investigate the impact of apron geometry, including its roughness and length, on downstream scouring. In present model, at first, the model was calibrated by simulating a physical model that investigated the scouring downstream of the apron under the influence of changes in apron roughness, particle densimetric Froude number, and gradation. Then the effect of changing the apron length on the maximum downstream scour depth was investigated numerically. Finally, a relationship for the maximum scour depth was proposed by using all the numerical model outputs. Selsby-Whitehouse equation was determined as the best method for calculating the critical Shields number, and the best results for the numerical model were obtained by selecting the bed load coefficient equal to 13. The comparison between the model outputs and the physical model results yielded satisfactory outcomes, demonstrating that the model can predict over 80% of the laboratory data with an error rate below 20%.